Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Unraveling molecular mechanisms underlying plant defense in response to dual insect attack : studying density-dependent effects
    Kroes, A. - \ 2016
    Wageningen University. Promotor(en): Marcel Dicke; Joop van Loon. - Wageningen : Wageningen University - ISBN 9789462577756 - 265
    016-3953 - arabidopsis thaliana - insect pests - herbivory - pest resistance - defence mechanisms - insect plant relations - molecular plant pathology - density - arabidopsis thaliana - insectenplagen - herbivorie - plaagresistentie - verdedigingsmechanismen - insect-plant relaties - moleculaire plantenziektekunde - dichtheid

    In the field, plants suffer from attack by herbivorous insects. Plants have numerous adaptations to defend against herbivory. Not only do these defense responses reduce performance of the feeding herbivore, they also result in the attraction of natural enemies of herbivores.

    The majority of studies investigating plant-insect interactions addressed mainly the effects of attack by a single herbivore species on induced plant defenses. However, because plants are members of complex communities, plants are exposed to different insect attackers at the same time. Moreover, attacks by different herbivores interact at different levels of biological organization, ranging from the level of gene expression, phytohormone production and biochemical changes up to the individual level. Effects of plant responses to feeding by two or more herbivore species simultaneously might cascade through the community and thereby affect insect community composition.

    The induction of plant defense responses is regulated by a network of signaling pathways that mainly involve the phytohormones jasmonic acid (JA), salicylic acid (SA) and ethylene (ET). The signaling pathways of the two phytohormones SA and JA interact antagonistically, whereas JA and ET signaling pathways can interact both synergistically and antagonistically in regulating plant defense responses. In general, JA-mediated signaling underlies defense responses against leaf-chewing herbivores, such as caterpillars, whereas phloem-feeding insects, such as aphids, mainly induce SA-regulated defenses.

    When caterpillars and aphids simultaneously feed on the same host plant, crosstalk between phytohormonal signaling pathways may affect the regulation of plant defenses. Consequently, multiple insect herbivores feeding on plants interact indirectly through plant-mediated effects. Studies investigating molecular mechanisms underlying interference by multiple attacking insects with induced plant defenses will benefit studies on the ecological consequences of induced plant responses.

    The aim of this thesis was to elucidate molecular mechanisms that underlie plant-mediated interactions between attacking herbivores from different feeding guilds, namely Brevicoryne brassicae aphids and Plutella xylostella caterpillars.

    Because herbivore density affects the regulation of plant defense responses, it may also influence the outcome of multiple insect-plant interactions. To study if modulation of induced plant defenses in response to dual insect attack depends on insect density, plants were infested with two densities of aphids.

    Responses of Arabidopsis thaliana plants to simultaneous feeding by aphids and caterpillars were investigated by combining analyses of phytohormone levels, defense gene expression, volatile emission, insect performance and behavioral responses of parasitoids. To better predict consequences of interactions between plants and multiple insect attackers for herbivore communities, the regulation of defense responses against aphids and caterpillars was also studied in the ecological model plant wild Brassica oleracea.

    Transcriptomic changes of plants during multiple insect attack and their consequences for the plant’s interactions with members of the associated insect community take place at different time scales. Direct correlation of transcriptomic responses with community development is, therefore, challenging. However, detailed knowledge of subcellular mechanisms can provide tools to address this challenge.

    One of the objectives of this thesis, therefore, was to investigate the involvement of phytohormonal signaling pathways and their interactions during defense responses against caterpillars or aphids at different densities, when feeding alone or simultaneously on the model plant A. thaliana. The studies show that aphids at different densities interfere in contrasting ways with caterpillar-induced defenses, which required both SA- and JA-signal-transduction pathways. Transcriptional analysis revealed that expression of the SA transcription factor gene WRKY70 was differentially affected upon infestation by aphids at low or high densities. Interestingly, the expression data indicated that a lower expression level of WRKY70 led to significantly higher MYC2 expression through SA-JA crosstalk. Based on these findings, it is proposed that by down-regulating WRKY70 expression, the plant activates JA-dependent defenses which could lead to a higher resistance against aphids and caterpillars.

    Plutella xylostella caterpillars also influenced plant defense responses when feeding simultaneously with aphids. Caterpillar feeding affected aphid-induced defenses which had negative consequences for aphid performance. Induction of both ET- and JA-mediated defense responses is required for this interference. Moreover, aphid density also played an important role in the modulation by P. xylostella of aphid-induced defenses: P. xylostella caterpillars induced changes in levels of JA and its biologically active from, JA-Ile, only when feeding simultaneously with aphids at a high density.

    To study the overall effect of dual herbivory on induced plant defenses, not only interference with induced direct defense, but also with induced indirect defenses was addressed in A. thaliana. We found a significant preference of the aphid parasitoid Diaeretiella rapae for volatiles from aphid-infested A. thaliana wild-type plants and ein2-1 (ET-insensitive) mutants. Interestingly, simultaneous feeding by P. xylostella caterpillars on wild-type plants increased D. rapae’s preference for odors from aphid-infested plants. However, upon disruption of the ET-signaling pathway, D. rapae did not distinguish between ein2-1 mutants infested by aphids or by both aphids and caterpillars. This showed that intact ET signaling is needed for caterpillar modulation of the attraction of D. rapae parasitoids.

    On the other hand, attraction of the caterpillar parasitoid Diadegma semiclausum to volatiles emitted by A. thaliana plants simultaneously infested by caterpillars and aphids was influenced by the density of the feeding aphids. Biosynthesis and emission of the terpene (E,E)-α-farnesene could be linked to the observed preference of D. semiclausum parasitoids for the HIPV blend emitted by plants dually infested by caterpillars and aphids at a high density, compared to dually infested plants with a low aphid density.

    Transcriptomic changes in the response of A. thaliana wild-type plants to simultaneous feeding by P. xylostella caterpillars and B. brassicae aphids compared to plants infested by P. xylostella caterpillars alone were assessed using a microarray analysis. I particularly addressed the question whether the transcriptomic response to simultaneously attacking aphids and caterpillars was dependent on aphid density and time since initiation of herbivory. The data show that in response to simultaneous feeding by P. xylostella caterpillars and B. brassicae aphids the number of differentially expressed genes was higher compared to plants on which caterpillars had been feeding alone. Additionally, specific genes were differentially expressed in response to aphids feeding at low or high density. Cluster analysis showed that the pattern of gene expression over the different time points in response to dual infestation was also affected by the density of the attacking aphids. These results suggest that insects attacking at a high density cause an acceleration in plant responses compared to insects attacking at low density.

    As a next step in the study of multiple interacting herbivores, I studied whether plant responses to dual herbivory have consequences for the performance of a subsequently arriving herbivore, Mamestra brassicae caterpillars. The ecological consequences of plant responses to dual herbivory cascading into a chain of interactions affecting other community members have remained unstudied so far. We used wild B. oleracea plants to evaluate dual herbivore-induced plant adaptations for subsequent herbivory. We found that simultaneous feeding by P. xylostella and B. brassicae resulted in different plant defense-related gene expression and differences in plant hormone levels compared to single herbivory, and this had a negative effect on subsequently arriving M. brassicae caterpillars. Differential induction of JA-regulated transcriptional responses to dual insect attack was observed which could have mediated a decrease in M. brassicae performance. The induction of plant defense signaling also affected both P. xylostella and B. brassicae performance. This study further helps to understand herbivore community build-up in the context of plant-mediated species interactions.

    Altogether, findings from this thesis reveal a molecular basis underlying plant responses against multiple herbivory and provide insight in plant-mediated interactions between aphids and caterpillars feeding on plants growing in the field or used in agriculture.

    Onderzoek naar betere schatting van de dichtheid van gras- en maiskuilen
    Zom, R.L.G. ; Abbink, G.W. ; Schooten, H.A. van - \ 2015
    Wageningen : Wageningen UR Livestock Research (Rapport / Wageningen UR Livestock Research 872) - 46
    graskuilvoer - kuilvoer - maïskuilvoer - dichtheid - voorraden - veevoeder - voedingswaarde - kuilvoerkwaliteit - lineaire modellen - regressieanalyse - grass silage - silage - maize silage - density - stocks - fodder - nutritive value - silage quality - linear models - regression analysis
    This report describes the results of a study on the possibilities to estimate the density of grass en maize silages for calculation of the fodder stock more accurately than the current table values. During ensiling the amount of crop of 104 grass silage clamps, 42 maize silage clamps and 108 big bales (54 round and 54 square) were weighted and after ensiling the dimensions were measured and the chemical composition was analysed. For round and square bales a new regression formula was derived, which estimates the density more accurate than the current table values. It is recommended to calculate the density of round en square bales with the following formula: Density (kg/m3) = 994.81 - 0.5335 x dry matter content (g/kg) - 1.196 x crude fibre content (g/kg ds). For grass en maize silage in clamps and bunker silo’s no new model could be derived which estimated the density more accurately than the current table values.
    The effect of harvesting on biomass production and nutrient removal in phototrophic biofilm reactors for effluent polishing
    Boelee, N.C. ; Janssen, M. ; Temmink, H. ; Taparaviciute, L. ; Khiewwijit, R. ; Janoska, A. ; Buisman, C.J.N. ; Wijffels, R.H. - \ 2014
    Journal of Applied Phycology 26 (2014)3. - ISSN 0921-8971 - p. 1439 - 1452.
    afvalwaterbehandeling - biofilms - dikte - dichtheid - algen - biologische waterzuiveringsinstallaties - fototropie - stikstof - fosfor - verwijdering - biobased economy - waste water treatment - biofilms - thickness - density - algae - biological water treatment plants - phototropism - nitrogen - phosphorus - removal - biobased economy - waste-water treatment - photosynthetic efficiency - chlorella-sorokiniana - microalgal biofilms - phosphorus removal - mass-transport - fresh-water - light - growth
    An increasing number of wastewater treatment plants require post-treatment to remove residual nitrogen and phosphorus. This study investigated various harvesting regimes that would achieve consistent low effluent concentrations of nitrogen and phosphorus in a phototrophic biofilm reactor. Experiments were performed in a vertical biofilm reactor under continuous artificial lighting and employing artificial wastewater. Under similar conditions, experiments were performed in near-horizontal flow lanes with biofilms of variable thickness. It was possible to maintain low nitrogen and phosphorus concentrations in the effluent of the vertical biofilm reactor by regularly harvesting half of the biofilm. The average areal biomass production rate achieved a 7 g dry weight m-2 day-1 for all different harvesting frequencies tested (every 2, 4, or 7 days), corresponding to the different biofilm thicknesses. Apparently, the biomass productivity is similar for a wide range of biofilm thicknesses. The biofilm could not be maintained for more than 2 weeks as, after this period, it spontaneously detached from the carrier material. Contrary to the expectations, the biomass production doubled when the biofilm thickness was increased from 130 µm to 2 mm. This increased production was explained by the lower density and looser structure of the 2 mm biofilm. It was concluded that, concerning biomass production and labor requirement, the optimum harvesting frequency is once per week.
    Experimenten met algenteelt: - effect van pH setpoints - effect van dichtheid
    Voogt, W. ; Hemming, S. ; Winkel, A. van - \ 2013
    algenteelt - ph - dichtheid - gewasproductie - chlorella sorokiniana - glastuinbouw - biobased economy - algae culture - ph - density - crop production - chlorella sorokiniana - greenhouse horticulture - biobased economy
    Poster met onderzoeksinformatie. Er wordt onderzoek gedaan naar effecten van pH setpoints en de dichtheid op groei en ontwikkeling van algen Chlorella sorokiniana.
    Beheersing van het wortellesieaaltje Pratylenchus penetrans
    Beers, T.G. van; Molendijk, L.P.G. - \ 2009
    Lelystad : PPO AGV (PPO-AGV / Rapport ) - 26
    gewasbescherming - proefvelden - experimenten - populatiedichtheid - populatie-ecologie - dichtheid - nematoda - aardappelen - plant protection - experimental plots - experiments - population density - population ecology - density - nematoda - potatoes
    Om te toetsen in hoeverre gecombineerde gelijktijdige besmettingen van verschillende aaltjessoorten elkaars ontwikkeling en de groei van de aardappelplanten beïnvloeden, is een pot experiment opgezet. Hierbij zijn onder kasomstandigheden in 5 kg potten met aardappel in kunstgrond dichthedenreeksen van G. pallida en P. penetrans, afzonderlijk en in combinatie met elkaar, aangebracht. Deze dichthedenreeksen liepen per aaltjessoort van 0 aaltjes per gram grond tot 128 aaltjes per gram grond, de gecombineerde besmetting was telkens 1:1. De verwachting was dat er bij oplopende dichtheden van (een van) beide aaltjes hinder in de populatieontwikkeling van één of beide aaltjes zou ontstaan. Dit bleek niet het geval. Ook ontstond er geen hinder in de bovengrondse groei. De ondergrondse groei, gemeten in de vorm van het versgewicht van de gevormde aardappelknollen was bij de hoogste dichtheden van de aaltjes wel gehinderd. Het maakte hierbij niet uit of het een enkelvoudige of een gecombineerde besmetting betrof.
    Verkeer is als water : verkeersoverlast te lijf met opschaling
    Stobbelaar, D.J. ; Jaarsma, C.F. ; Hoofwijk, H. ; Simons, M.J.A. - \ 2008
    ROM : maandblad voor ruimtelijke ontwikkeling 25 (2008)1/2. - ISSN 1571-0122 - p. 34 - 37.
    wegtransport - platteland - verkeer - dichtheid - monitoring - verkeerspatronen - noord-brabant - road transport - rural areas - traffic - density - monitoring - traffic patterns - noord-brabant
    Veel kleine kernen hebben in toenemende mate last van verkeersdruk. Oplossingen die de gemeentegrenzen net overstijgen, zijn meestal niet afdoende. Een onderzoeksteam van Wageningen UR zoekt de oplossing in Erp in de combinatie van interactieve planvorming, het weerstandenmodel en werken op een hoger schaalniveau
    Dichtheidsbepaling maïs- en graskuilen met boormonsters = Defining density of maize and grass silages through core samples
    Schooten, H.A. van; Dongen, C.A. - \ 2007
    Lelystad : Animal Sciences Group (Rapport / Animal Sciences Group 64) - 23
    maïskuilvoer - graskuilvoer - dichtheid - kernmonstertrekkers - dierhouderij - maize silage - grass silage - density - core samplers - animal husbandry
    In 2006 is onderzoek gedaan naar de dichtheid van 13 maïs- en 9 graskuilen. Bijstelling naar boven van de oude dichtheidsnormen van maïs- en graskuilen met resp. 20 en 10% lijkt gerechtvaardigd. In de praktijk is bij de meeste maïs- en graskuilen niet mogelijk is om met een beperkt aantal boringen de dichtheid te voorspellen
    Verkeer is als water... : overlast, veiligheid, bereikbaarheid en landschapskwaliteit in de casus Erp, Brabant
    Hoofwijk, H. ; Stobbelaar, D.J. ; Simons, M.J.A. ; Jaarsma, C.F. - \ 2007
    Wageningen : WUR, Wetenschapswinkel (Rapport / Wetenschapswinkel Wageningen UR 235) - ISBN 9789085850779 - 77
    wegtransport - platteland - dichtheid - monitoring - verkeer - verkeerspatronen - nederland - noord-brabant - road transport - rural areas - density - monitoring - traffic - traffic patterns - netherlands - noord-brabant
    Verkeersdruk zorgt voor overlast in het dorp Erp. Al jaren wordt gepraat over een oplossing voor dit probleem. Recentelijk heeft deze discussie meer vaart gekregen door het voornemen van de gemeenteraad een rondweg om Erp aan te leggen. Reden om Wageningen UR de verkeersstromen te laten onderzoeken, om uit de impasse te komen. De overlast blijkt te bestaan uit twee los van elkaar staande verkeersstromen: verkeer dat dóór het verblijfsgebied rijdt (met name verkeer dat Boekel en Erp gebruikt om naar Veghel en ’s Hertogenbosch te gaan) en verkeer van binnen het verblijfsgebied (in deze verkeersstroom is het vooral het vrachtverkeer van en naar het industrieterrein dat overlast veroorzaakt). Deze twee verkeersstromen staan niet alleen los van elkaar, ze verschillen ook in niveau: regionaal versus lokaal.
    Vloeistofscheiden rekent af met slechte zaden
    Derkx, M.P.M. - \ 2007
    De Boomkwekerij 2007 (2007)1. - ISSN 0923-2443 - p. 14 - 15.
    zaadkwaliteit - zaden - dichtheid - selectie - scheiding - boomkwekerijen - seed quality - seeds - density - selection - separation - forest nurseries
    Men kan slechte zaden onderscheiden van goede zaden door middel van de dichtheid, hoe lager de dichtheid hoe slechter het zaad. Zaden kunnen zo worden gescheiden van elkaar met behulp van vloeistoffen van verschillende dichtheden. Zaad kan zo veel efficienter worden gebruikt en de kwaliteit worden verhoogd door alleen de beste kwaliteit te gebruiken.
    De ontwikkeling van de Japanse oester in de Nederlandse Waddenzee: Situatie 2006
    Fey-Hofstede, F.E. ; Dankers, N.M.J.A. ; Meijboom, A. ; Jong, M.L. de; Leeuwen, P.W. van; Dijkman, E.M. ; Cremer, J.S.M. - \ 2007
    Den Burg : IMARES (Rapport / IMARES 07.003) - 23
    crassostrea gigas - mariene ecologie - aquatische ecologie - onderzoek - dichtheid - waddenzee - crassostrea gigas - marine ecology - aquatic ecology - research - density - wadden sea
    In de Waddenzee werd de eerste Japanse oester waargenomen in 1983 bij de haven van Oudeschild, Texel. Rond het begin van de 21ste eeuw werd duidelijk dat de Japanse oester over de gehele Waddenzee voorkomt. Sinds 2002 wordt de ontwikkeling van enkele individuele oesterbanken in de Nederlandse Waddenzee gevolgd. In deze rapportage wordt een beschrijving gegeven van de ontwikkeling van deze individuele oesterbanken tot 2006. Op alle gevolgde locaties zijn op den duur oesterriffen ontstaan met verschillende jaarklassen. Het lijkt erop dat de dichtheden en oppervlakten op sommige locaties niet verder toenemen. Om inzicht te krijgen in groei en afname in dichtheden en oppervlakte van individuele oesterriffen is het van belang de ontwikkelingen van individuele oesterriffen te blijven volgen. Aangezien oesters een voorkeur lijken te hebben om zich op andere oesters te vestigen, is de verwachting dat er zich op meer plekken oesterriffen zullen ontwikkelen. Om inzicht te krijgen in de ontwikkeling van de Japanse oester in de Nederlandse Waddenzee is het van groot belang om een kwantitatieve monitoring op te zetten die speciaal gericht is op het vaststellen van de biomassa en verspreiding van de Japanse oester. Daarnaast is het noodzakelijk het ecologisch belang van dit nieuwe en blijvende habitattype nader te bestuderen
    Duurzame mobiliteit en vrijetijdsverkeer in het metropolitane buitengebied: paradox of realiseerbaar? Op weg naar een onderzoeksagenda
    Jaarsma, C.F. ; Dijk, T. van; Heijman, W.J.M. - \ 2005
    In: Duurzame mobiliteit: hot or not?, 32e Colloquium Vervoersplanologisch Speurwerk, Antwerpen, 24-25 november 2005. - Rotterdam : Stichting CVS (Colloquium Vervoersplanologisch speurwerk - p. 581 - 600.
    wegtransport - dichtheid - openluchtrecreatie - infrastructuur - road transport - density - outdoor recreation - infrastructure
    Met het verder verstedelijken van ons land vervagen de traditionele grenzen tussen stad en land. Door deze ontwikkeling naar een metropolitaan landschap wordt de open ruimte tussen grote steden, het metropolitane buitengebied, steeds belangrijker voor de stedeling als ruimte om zich te bewegen en te ontspannen. Echter, de bereikbaarheid en de aantrekkelijkheid van dit landschap staat damee onder druk. Uiteindelijk komt de stedeling (met het bereiken van deze gebieden en de benodigde infrastructuur) in conflict met zijn eigen wensen
    Monitoringsonderzoek recreatie duingebied Meijendel - deel XVI; Analyse van het recreatieverkeer en het recreatiebezoek in de periode maart 2004 - februari 2005
    Webster, M.J. ; Beunen, R. ; Jaarsma, C.F. - \ 2005
    Wageningen : WUR, Leerstoelgroep Landgebruiksplanning (Nota / Vakgroep Ruimtelijke Planvorming nr. 101) - ISBN 9789067549677 - 92
    recreatieonderzoek - duingebieden - openluchtrecreatie - recreatie - projecten - monitoring - bezoekers - wegtransport - verkeer - dichtheid - tijd - nederland - zuid-holland - leisure research - duneland - outdoor recreation - recreation - projects - monitoring - visitors - road transport - traffic - density - time - netherlands - zuid-holland
    Recreatieonderzoek Wageningen
    Verkeersmonitoring Posbank gebied; Analyse van het recreatieverkeer en het autobezoek in de periode november 2002 - oktober 2003
    Beunen, R. ; Jaarsma, C.F. - \ 2004
    Wageningen : WUR, Leerstoelgroep Landgebruiksplanning (Nota / Wageningen Universiteit, Leerstoelgroep Landgebruiksplanning nr. 97) - ISBN 9789067547871 - 64
    verkeer - wegtransport - dichtheid - tellen - recreatieonderzoek - recreatie - onderzoek - methodologie - projecten - monitoring - karteringen - gegevensanalyse - nederland - veluwe - traffic - road transport - density - counting - leisure research - recreation - research - methodology - projects - monitoring - surveys - data analysis - netherlands - veluwe
    Reducing habitat fragmentation on minor rural roads through traffic calming
    Jaarsma, C.F. ; Willems, G.P.A. - \ 2002
    Landscape and Urban Planning 58 (2002). - ISSN 0169-2046 - p. 125 - 135.
    territorium - verkeer - dichtheid - nadelige gevolgen - plattelandswegen - habitatfragmentatie - territory - traffic - density - adverse effects - rural roads - habitat fragmentation
    The rural road network suffers continually from ambiguity. On the one hand, the presence of this network and its traffic flows offer accessibility and make a contribution to economic development. While on the other, its presence and its traffic flows cause fragmentation. The actual ecological impact of this fragmentation depends on several variables such as species and road characteristics. This paper focuses on minor rural roads. The spatial concept developed to address this, `traffic calming rural area' (TCRA) is intended to address both accessibility and sustainable environment. It does this by concentrating the current diffuse traffic flows on a few rural highways, thus, creating rural residential areas within the region. This paper presents some formulae to quantify the resulting fragmentation. A more practical method compares the sizes of continuous landscape units. Both the formulae and the method have been used for two pilot studies. The results indicate that implementing the TCRA concept leads to larger continuous landscape units, thereby helping to reduce fragmentation effects
    Monitoringsonderzoek recreatie duingebied Meijendel - deel XII. Analyse van het recreatieverkeer en het recreatiebezoek in de periode maart 2001 - februari 2002
    Beunen, R. ; Webster, M.J. ; Jaarsma, C.F. - \ 2002
    Wageningen : Wageningen UR (Nota Vakgroep Ruimtelijke Planvorming 92) - ISBN 9789067546850 - 98
    recreatieonderzoek - recreatie - onderzoek - methodologie - projecten - monitoring - dichtheid - wegtransport - verkeer - tellen - budgetten - tijd - duinen - eolisch zand - nederland - karteringen - gegevensanalyse - zuid-holland - leisure research - recreation - research - methodology - projects - density - road transport - traffic - counting - budgets - time - dunes - aeolian sands - netherlands - surveys - data analysis
    Monitoringsonderzoek recreatie duingebied Meijendel - deel XI. Analyse van het recreatieverkeer en het recreatiebezoek in de periode maart 2000 - februari 2001
    Beunen, R. ; Jaarsma, C.F. ; Webster, M.J. - \ 2001
    Wageningen : Wageningen UR (Nota vakgroep Ruimtelijke Planvorming 91) - ISBN 9789067546614 - 100
    vrije tijd - onderzoek - gegevensanalyse - recreatie - methodologie - projecten - monitoring - bezoekers - wegtransport - verkeer - dichtheid - tellen - tijd - nederland - zuid-holland - leisure - research - data analysis - recreation - methodology - projects - visitors - road transport - traffic - density - counting - time - netherlands
    The effect of fish on plankton dynamics : a theoretical analysis
    Scheffer, M. ; Rinaldi, S. ; Kuznetsov, Y.A. - \ 2000
    Canadian Journal of Fisheries and Aquatic Sciences 57 (2000)6. - ISSN 0706-652X - p. 1208 - 1219.
    vissen - plankton - algen - daphnia - dichtheid - biomassa - onderzoek - fishes - plankton - algae - daphnia - density - biomass - research
    We present an expansion of a classical minimal Daphnia–algae model to account for effects of fish as a top predator. Our analyses suggest that in most situations, the plankton should show hysteresis in response to predation pressure by fish. Thus, there exist two distinct regimes, one in which Daphnia is controlled (overexploited) by fish and phytoplankton biomass is high and another in which Daphnia is relatively unaffected (underexploited) by planktivores and algae are controlled by Daphnia. Switches from one regime to the other occur abruptly at a critical fish density. This is in line with field observations and experimental results. Our model predicts that the critical fish density for Daphnia collapse is higher in systems with higher ambient nutrient concentrations. The model also shows how intrinsic predator–prey oscillations in the planktonic system can facilitate the switch to the algal-dominated regime where Daphnia is controlled by fish. In terms of dynamical systems theory, this switch happens through a homoclinic bifurcation. In biological terms, Daphnia collapses due to food limitation and is subsequently overexploited by fish. This is indeed the sequence of mechanisms observed at the end of the spring clearwater phase in lakes where Daphnia is absent during the summer when the biomass of young-of-the-year planktivorous fish becomes high.
    Methode voor het bepalen van aslastpatronen voor plattelandswegen
    Wilde, J.G.S. de - \ 1998
    Wageningen : DLO-Staring Centrum (Rapport / DLO-Staring Centrum 518) - 39
    verkeer - verkeerspatronen - dichtheid - capaciteit - tellen - onderzoek - voertuigen - rolweerstand - wegen - plattelandswegen - wegtransport - basisproducten - traffic - traffic patterns - density - capacity - counting - research - vehicles - rolling resistance - roads - rural roads - road transport - commodities
    Verkeersintensiteit van zwaar verkeer op plattelandswegen in 1990 - 1995
    Wilde, J.G.S. de - \ 1997
    Wageningen : DLO-Staring Centrum (Rapport / DLO-Staring Centrum 480) - 49
    dichtheid - wegtransport - verkeer - tellen - basisproducten - plattelandswegen - bedrijfswegen - nederland - density - road transport - traffic - counting - commodities - rural roads - farm roads - netherlands
    Elektronische telapparatuur is bij vorst onbetrouwbaar. Om de jaarintensiteit te berekenen moet voor de vorstperioden een schatting worden gemaakt. De jaarintensiteit is een cruciale schakel bij het ophogen van dag- naar jaarwaarden, die een grote besparing oplevert bij het onderzoek naar de verkeersbelasting. De schatting wordt gemaakt door te vergelijken met resultaten van mechanische telapparatuur. Het zware verkeer bedraagt slechts 4% van al het gemotoriseerde verkeer, hoewel dit aandeel sterk schommelt en groter is naarmate de weg smaller is. Op de smalste wegen komt in de oogstperiode 27% meer zwaar verkeer voor dan in het poot- en groeiseizoen. Op de andere wegen is dit omgekeerd.
    Snelheden op plattelandswegen
    Wilde, J.G.S. de - \ 1997
    Wageningen : DLO-Staring Centrum (Rapport / DLO-Staring Centrum 488) - 45
    verkeer - snelheid - dichtheid - wegtransport - tellen - plattelandswegen - bedrijfswegen - nederland - traffic - velocity - density - road transport - counting - rural roads - farm roads - netherlands
    Effects of road density; a case study of the moor frog.
    Vos, C.C. - \ 1997
    In: Habitat fragmentation & infrastructure : proceedings of the international conference "Habitat fragmentation, infrastructure and the role of ecological engineering", 17 - 21 September 1995, Maastricht - The Hague, The Netherlands. - - p. 93 - 97.
    verkeer - verkeerspatronen - dichtheid - capaciteit - tellen - onderzoek - dieren - territorium - habitats - milieu - anura - kikkers - padden - multivariate analyse - correlatieanalyse - regressieanalyse - nadelige gevolgen - milieueffect - menselijke activiteit - traffic - traffic patterns - density - capacity - counting - research - animals - territory - environment - frogs - toads - multivariate analysis - correlation analysis - regression analysis - adverse effects - environmental impact - human activity
    Berekening van de verkeersstromen in de ruilverkaveling Melderslo met het verkeersmodel voor landelijke gebieden.
    Baltjes, C.R. ; Jaarsma, C.F. - \ 1992
    Wageningen : LU - 48
    computersimulatie - tellen - dichtheid - ruilverkaveling - landgebruik - ruimtelijke ordening - wegtransport - plattelandsgemeenschappen - simulatie - simulatiemodellen - verkeer - nederland - limburg - computer simulation - counting - density - land consolidation - land use - physical planning - road transport - rural communities - simulation - simulation models - traffic - netherlands - limburg
    Physical aspects of liquid-impelled loop reactors
    Sonsbeek, H. van - \ 1992
    Agricultural University. Promotor(en): J. Tramper. - S.l. : [s.n.] - 135
    chemische reacties - uitrusting - massaoverdracht - vloeistofmechanica - vloeistoffen (liquids) - vloeistoffen (fluids) - vermenging - dichtheid - chemical reactions - equipment - mass transfer - fluid mechanics - liquids - fluids - mixing - density

    The liquid-impelled loop reactor (LLR) is a reactor that consists of two parts : the main tube and the circulation tube. Both parts are in open connection at the bottom and at the top. The reactor is filled with a liquid phase: the continuous phase. Another liquid phase is injected in the main tube by means of pumping. This liquid phase is immiscible with the continuous phase and its density is significantly different. If the density is higher than the density of the continuous phase, injection takes places at the top of the main tube. For a lower density injection takes place at the bottom. Due to the density difference the dispersed-phase droplets that are formed will fall or rise, respectively, and coalesce at the other end of the tube. The coalesced liquid is discharged from the reactor. Due to the presence of dispersed phase in the main tube a pressure difference exists which causes circulation of the continuous phase in the reactor. This results in good mixing without the use of an impeller. For biotechnological purposes it is most likely that the continuous phase is an aqueous phase that contains the biocatalyst, possibly immobilized. The work on the liquid-impelled loop reactor originates from two previous research studies. First, the physical characterisation and modelling of air-lift loop reactors for application in cultivating shear-sensitive biocatalysts. Second, the research focused on application of organic solvents in biological processes, which is a promising area for many years already.

    In a review the current state of the art is given with respect to biocatalysis in media consisting of two liquid phases that are not miscible. This research area has shown much progress in recent years, however, industrial applications seem still not very numerous. To carry out two-liquid-phase experiments on a scale bigger than shake flasks, in most cases existing bioreactors are used. Adjustments are made to the reactor and the processing to make them suitable for use with two liquid phases. The liquid-impelled loop reactor can be seen as a special case, where an air-lift loop reactor is adjusted for use with two liquid phases instead of a liquid and a gas phase.

    The research was started with characterisation of important physical aspects such as drop size, dispersed-phase concentration (holdup) and continuous-phase velocity as function of the dispersed-phase flow rate. Description of drop sizes that are formed in the liquid-impelled loop reactor at the liquid sparger, show good agreement with theoretical predictions. The hydrodynamic model that was used in the air-lift loop study is applied. It shows to be a good method to describe holdup and liquid velocity. The best results with this model are obtained when it is assumed that the continuous phase flows fastest in the centre of the tube and that the dispersed phase concentrates in the centre of the tube.

    On the topic of hydrodynamic models for air-lift loop reactors many articles are published. Because this still continues, this literature is analysed and the basic principles of the several models are described and compared. It appears that in all models the relative velocity between dispersed-phase bubbles and continuous phase plays an essential role. This quantity is difficult to determine and shows a wide spread due to the distribution in bubble size. Furthermore, velocity profiles or turbulence can have much influence but are not taken into account in the described models. Comparison of the models by means of using literature data did not yield a clear preference for one of the models nor for a particular basic principle.

    To describe mixing in the continuous phase, the one-dimensional axial dispersion model is used, which is in general suitable for flow in tubular devices. The mixing parameter is determined per reactor section. For the main tube a correlation between mixing parameter and energy dissipation is given. The mixing parameter can be used to describe the flow of the continuous phase as a plug flow with axial disturbances. Furthermore, dimensionless mixing times can be estimated. The dimensionless mixing time is the number of circulations that is necessary to achieve complete mixing of the continuous phase, where the criterium must be defined by the user.

    Mass transfer is investigated in an FC40 water system. For this purpose a new method is developed based on the principle of a steady-state measurement, in stead of the most widely used dynamic measurement. Compared to a gas/liquid system at equal dispersed-phase flow rates, the mass-transfer rate in the liquid/liquid system is favorable. This is due to the larger exchange area, because the drops are smaller than the bubbles and the drop velocity relative to the continuous phase is lower than the relative velocity of the bubbles. The mass-transfer coefficient for the liquid/liquid system, derived from experimental results, however, is lower than literature values for gas/liquid systems. This is probably caused by the lower diffusion coefficient of oxygen in liquid than of oxygen in gas. The transfer capacity can often be the highest for gas/liquid systems because the maximum dispersed-phase flow rate in liquid/liquid systems is limited with respect to drop formation and coalescence. Further physical reseach must be focussed on this limitation.

    Onderzoek probleemsituaties 80 km/u-wegen, fase 2: Beschrijving van enkele ongevals- en wegkenmerken
    Michels, T. ; Meijer, E. - \ 1989
    Wageningen : ICW (ICW nota 1957) - 17
    tellen - dichtheid - nederland - wegtransport - plattelandswegen - verkeer - counting - density - netherlands - road transport - rural roads - traffic
    Verslag van de conferentie "Road traffic monitoring" (RTM) te Londen, 7 - 9 februari 1989
    Wilde, J.G.S. de - \ 1989
    Wageningen : ICW (ICW nota 1956) - 17
    tellen - dichtheid - groot-brittannië - wegtransport - verkeer - counting - density - great britain - road transport - traffic
    Vergelijking van verkeerskarakteristieken voor (1985) en na (1988) de realisatie van de proefwindcentrale bij Oosterbierum.
    Baltjes, C.R. ; Jaarsma, C.F. - \ 1989
    Wageningen : L.U. - 39
    tellen - dichtheid - energie - motoren - ruimtelijke ordening - openbare voorzieningen - wegtransport - verkeer - transport - nuttig gebruik - wind - windenergie - nederland - uitrusting - friesland - schema's - counting - density - energy - engines - physical planning - public utilities - road transport - traffic - transport - utilization - wind - wind power - netherlands - equipment - friesland - schedules
    Natuur- en landschapsaspecten van plattelandswegen. Enkele impressies uit West-Duitsland.
    Jaarsma, C.F. ; Michels, Th. - \ 1989
    Landinrichting 29 (1989)3. - ISSN 0922-6419 - p. 27 - 31.
    plattelandswegen - dichtheid - wegtransport - verkeer - tellen - bedrijfswegen - onderzoek - landbouwgrond - landschap - bondsrepubliek duitsland - rural roads - density - road transport - traffic - counting - farm roads - research - agricultural land - landscape - german federal republic
    Verkeersplanning in landelijke gebieden: methode voor het kwantificeren van verkeerskundige effecten, toegepast op het Binnenveld.
    Jaarsma, C.F. ; Michels, Th. - \ 1989
    Wageningen : Staring Centrum - 32
    tellen - dichtheid - wegtransport - plattelandswegen - verkeer - nederland - gelderland - gelderse vallei - counting - density - road transport - rural roads - traffic - netherlands - gelderland - gelderse vallei
    Plattelandswegen planmatig aanpakken.
    Jaarsma, C.F. - \ 1989
    Landbouwkundig Tijdschrift 101 (1989)11. - ISSN 0927-6955 - p. 25 - 28.
    tellen - dichtheid - bedrijfswegen - landgebruik - bedrijfsvoering - nederland - wegtransport - plattelandsontwikkeling - plattelandsplanning - plattelandswegen - verkeer - counting - density - farm roads - land use - management - netherlands - road transport - rural development - rural planning - rural roads - traffic
    Karakteristieken van het verkeer naar openluchtrecreatieprojecten.
    Jaarsma, C.F. ; Hoorn, A. van; Bruin, A.H. de - \ 1989
    Landinrichting 29 (1989)4. - ISSN 0922-6419 - p. 1 - 8.
    tellen - dichtheid - nederland - recreatie - wegtransport - verkeer - transport - counting - density - netherlands - recreation - road transport - traffic - transport
    Plattelandswegen en de ontsluiting van Landelijke gebieden: pleidooi voor een planmatige aanpak buiten landinrichtingsprojecten.
    Jaarsma, C.F. - \ 1989
    Planologische diskussiebijdragen (1989). - ISSN 0923-8948 - p. 313 - 322.
    tellen - dichtheid - bedrijfswegen - landgebruik - bedrijfsvoering - nederland - wegtransport - plattelandsontwikkeling - plattelandsplanning - plattelandswegen - verkeer - counting - density - farm roads - land use - management - netherlands - road transport - rural development - rural planning - rural roads - traffic
    Monitoring van de visstand in het Nederlandse deel van de stroomgebieden van Rijn en Maas in 1987
    Cazemier, W.G. ; Heermans, W. - \ 1988
    IJmuiden : Rijksinstituut voor Visserijonderzoek (Rapport / Rijksinstituut voor Visserijonderzoek BV 88-01)
    biologische indicatoren - samenstelling - dichtheid - indicatoren - visstand - maas - rijn - biological indicators - composition - density - indicators - fish stocks - river meuse - river rhine
    Onderzoek probleemsituaties 80 km/u-wegen, fase 2: Kwantitatieve analyse
    Michels, T. ; Meijer, E. - \ 1988
    Wageningen : ICW (ICW nota 1922)
    tellen - dichtheid - nederland - wegtransport - plattelandswegen - verkeer - counting - density - netherlands - road transport - rural roads - traffic
    Onderzoek probleemsituaties 80 km/u-wegen, fase 2: Kwalitatieve analyse
    Michels, T. ; Meijer, E. - \ 1988
    Wageningen : ICW (ICW nota 1927)
    tellen - dichtheid - nederland - wegtransport - plattelandswegen - verkeer - counting - density - netherlands - road transport - rural roads - traffic
    Verkeerstellingen rondom de proefwindcentrale bij Oosterbierum. Vervolgonderzoek 1988.
    Baltjes, C.R. ; Jaarsma, C.F. - \ 1988
    Wageningen : Baltjes [etc.] - 23
    tellen - dichtheid - energie - motoren - meting - ruimtelijke ordening - openbare voorzieningen - wegtransport - verkeer - nuttig gebruik - wind - windenergie - nederland - uitrusting - friesland - counting - density - energy - engines - measurement - physical planning - public utilities - road transport - traffic - utilization - wind - wind power - netherlands - equipment - friesland
    Druktebeleving van fietsende recreanten : een onderzoek op plattelandswegen in de omgeving van Zwolle
    Klinkers, P.M.A. ; Hoorn, A. van - \ 1987
    Wageningen : ICW (ICW nota 1805) - 54
    fietsen - kleur - tellen - dichtheid - eerste hulp - openluchtrecreatie - perceptie - recreatie - wegtransport - recreatie op het platteland - plattelandswegen - tijd - toerisme - verkeer - verkeersongevallen - transport - Nederland - overijssel - ruimte - bicycling - colour - counting - density - first aid - outdoor recreation - perception - recreation - road transport - rural recreation - rural roads - time - tourism - traffic - traffic accidents - transport - Netherlands - overijssel - space
    Onderzocht is wat het verband is tussen de druktebeleving van fietsers en de vervoersintensiteit op plattelandswegen in de omgeving van Zwolle. Tevens is nagegaan of er een verband bestaat tussen de druktebeleving en de sociale en persoonskenmerken van de fietser. Tenslotte is bekeken wat voor de fietsende recreant het belang is van drukte als hinderfactor t.o.v. andere hinderende factoren.
    Marktverkenning verkeersregistratie - apparatuur
    Heijden, T.G.C. van der - \ 1987
    Wageningen : ICW (Nota / Instituut voor Cultuurtechniek en Waterhuishouding 1777) - 27
    constructie - tellen - dichtheid - instrumentatie - instrumenten (meters) - fabricage - meting - wegtransport - verkeer - construction - counting - density - instrumentation - instruments - manufacture - measurement - road transport - traffic
    Landbouwgebonden vrachtverkeer : verkenning en onderzoeksvoorstel
    Heijden, T.G.C. van der - \ 1987
    Wageningen : ICW (Nota / Instituut voor Cultuurtechniek en Waterhuishouding 1758) - 25
    basisproducten - tellen - dichtheid - nederland - wegtransport - plattelandswegen - verkeer - transport - commodities - counting - density - netherlands - road transport - rural roads - traffic - transport
    Buitenlandse ontwikkelingen in het onderzoek rond plattelandswegen.
    Michels, Th. ; Jaarsma, C.F. - \ 1987
    Wageningen : I.C.W. (Nota / Instituut voor Cultuurtechniek en Waterhuishouding 1776) - 80
    tellen - dichtheid - bondsrepubliek duitsland - infrastructuur - onderzoek - wegtransport - wegen - plattelandswegen - zwitserland - verkeer - counting - density - german federal republic - infrastructure - research - road transport - roads - rural roads - switzerland - traffic
    Verslag van mechanische verkeerstellingen in het Wageningse Binnenveld (1983 en 1984).
    Baltjes, C.R. ; Jaarsma, C.F. - \ 1986
    Wageningen : L.H. - 55
    tellen - dichtheid - wegtransport - verkeer - nederland - gelderland - gelderse vallei - counting - density - road transport - traffic - netherlands - gelderland - gelderse vallei
    Informatiesysteem wegen landinrichting : nadere uitwerking en proefopzet
    Heijden, T.G.C. van der - \ 1985
    Wageningen : ICW (Nota / Instituut voor Cultuurtechniek en Waterhuishouding no. 1572) - 20
    computers - tellen - gegevensverwerking - dichtheid - ruilverkaveling - landgebruik - bedrijfsvoering - microcomputers - minicomputers - ruimtelijke ordening - wegtransport - plattelandsontwikkeling - plattelandsplanning - plattelandswegen - verkeer - machines - computers - counting - data processing - density - land consolidation - land use - management - microcomputers - minicomputers - physical planning - road transport - rural development - rural planning - rural roads - traffic - machines
    Als basis voor de planvorming in het kader van projectvoorbereiding dient een groot aantal weg-, verkeers- en wegenbouwkundige kenmerken te worden gekwantificeerd. De Werkgroep Wegenbestand Landinrichting heeft een systeem voorgesteld, waarbij benodigde gegevens op efficiente wijze kunnen worden verzameld
    Een proefneming met telapparatuur voor de registratie van fietsen, bromfietsen en motorvoertuigen
    Klinkers, P.M.A. - \ 1985
    Wageningen : ICW (Nota / Instituut voor Cultuurtechniek en Waterhuishouding no. 1643) - 12
    fietsen - tellen - dichtheid - wegtransport - verkeer - bicycling - counting - density - road transport - traffic
    Ontwikkeling en toepassing van een schattingsmethode voor het jaarbezoek aan strandbad Nulde-Horst
    Jaarsma, C.F. ; Voet, J.L.M. van der - \ 1985
    Recreatie en Toerisme 17 (1985)6. - ISSN 0165-4179 - p. 294 - 298.
    budgetten - capaciteit - tellen - dichtheid - meren - recreatieonderzoek - nederland - openluchtrecreatie - recreatie - onderzoek - zwembaden - tijd - verkeer - verkeerspatronen - transport - budgets - capacity - counting - density - lakes - leisure research - netherlands - outdoor recreation - recreation - research - swimming pools - time - traffic - traffic patterns - transport
    Verkeerstellingen rondom het te bouwen windmolenpark bij Sexbierum in 1984
    Baltjes, C.R. ; Jaarsma, C.F. - \ 1985
    Wageningen : L.H. - 26
    tellen - dichtheid - wegtransport - verkeer - nederland - friesland - counting - density - road transport - traffic - netherlands - friesland
    Verkeer in een landelijk gebied : waarnemingen en analyse van het verkeer in zuidwest Friesland en ontwikkeling van een verkeersmodel
    Jaarsma, C.F. - \ 1984
    Landbouwhogeschool Wageningen. Promotor(en): F. Hellinga. - Wageningen : Jaarsma - 382
    tellen - dichtheid - modellen - wegtransport - verkeer - transport - reizen - nederland - friesland - counting - density - models - road transport - traffic - transport - travel - netherlands - friesland

    Transport, the transfer of people or goods, lays at the basis of our welfare. Traffic is the collectivity of moving means of transport. Road traffic especially has grown explosively during the last decades (fig. 1.1). In certain cases these effects (safety; noise; visual annoyance and environment) are radical and inconvenient. Difficulties caused by the extending traffic were revealed at first in the cities and on the main roads, but problems arose in the rural areas also.

    The study described in this dissertation is concerned with traffic in rural areas. The South-West of the province of Friesland has been chosen as the study area. Because road networks should be considered as a connected system, the research is not restricted to rural roads (the agricultural road network) but is also considering the main road network in the rural area (rural highways).

    In chapter 2 extension and development of traffic since 1945 is the main item. Attention is paid to traffic research and community concerns with expanding road traffic. Section 2.2 deals with The Netherlands as a whole; in section 2.3 special attention is given to the rural areas.

    On the Dutch road network there has been a considerable growth in the volume of motorvehicle traffic: roughly speaking it doubled between 1960 and 1970. It grew by more than 50% during the period from 1970 to 1980. Since 1980 it more or less stabilized (fig. 2.2.1).

    Within the category of motorvehicles growth is greatest for cars, which has greatly changed traffic composition (table 2.2.5).

    At first the reaction of our society to growing mobility was positive. A drastic expansion of the surfaced road network was effected, particularly since the early sixties. In the "Tweede Nota over de Ruimtelijke Ordening" (Second Report on Physical Planning), published in 1966, a rectangular network of main roads was designed (total length 5300 km), whereby larger cities are surrounded by one or two networks. The necessity of a more fundamental (model)study of traffic volumes became evident in those years.

    In the years afterwards more attention was paid to the harmful effects of especially mobility by car, on the environment and livability of inner cities. In 1972 the results of "COVW" (Committee Promotion Public Transport in Western Netherlands) and "NEI-Studie" (Study of the Dutch Economic Research Institute) became available. The results of these studies indicate radical consequences of traffic growth if governmental policy remains unchanged. Because these consequences are considered undesirable the predominantly "following policy" regarding development of traffic has gradually been replaced by a "steering policy" ever since 1979.

    The actual long term policy for transport and traffic is described in the "SVV" (Structure Scheme for Traffic and Transport), in which an outline is given of the network of main roads. The total length amounts to about 3400 km, of which 2460 km was realised in 1979. The elaboration of this policy on the short term' takes place in the "MPP" (4-year Program for Traffic and Transport).

    Data on the development of the traffic volume in rural areas are scarce. On the so called 28-points census of the "Landinrichtingsdienst" (Governmental Service of Land Use Planning, abbreviation LD) respectively 294, 406 and 560 personal car units were observed in the years 1962, 1967 and 1972. The number of bicycles and mopeds on these observation points remains nearly constant, but from point to point fluctuation is considerable. The increasing volume is caused by an increasing number of cars. This also appears from an analysis of traffic composition (table These developments are caused by the increase in size and the mechanisation of agricultural holdings, the multiple use of the rural area for outdoor recreation and the increase in the use of minor roads to avoid possible delay on major roads (the so called rat-run traffic).

    The governmental policy with respect to rural roads was published in the "Landbouwwegennota" (Report for Agricultural Roads) in 1954, in the "Plattelandswegennota" (Report for Rural Roads) in 1969 and in the "SLI" (Structure Scheme for Land Use Planning) in 1981. In the SLI the objectives of road development in the rural areas are given. Examples of these objectives are an appropriate and safe access related to the different functions of the rural area, and an expansion of the opportunities for multiple use of land.

    At first the research for rural traffic was almost exclusively directed towards the so called internal farm traffic, of which traffic with farm equipment is the most important feature.

    An extension of the research into external farm traffic is evident. In this traffic lorries, often bulk- or milktank lorries, take an important place.

    In some areas recreational traffic, especially cars, can be very extensive also needs further research.

    In The Netherlands nearly all rural roads are used by all forms of traffic. Therefore the internal and external farm traffic and recreational traffic are part of the total rural traffic. The most important problems concern traffic with farm equipment (moving characteristics), traffic with lorries (road construction, design of roads) and traffic with cars (width of the road). These problems should be solved on a regional basis. Therefore a more precise insight into the present and future traffic volumes and their influencing factors is needed. Transportation models for calculation of link loads up to now hardly applied for rural traffic - seem to be useful.

    With reference to the foregoing, the study described in this dissertation was undertaken, with the following three interconnected objectives:
    - to obtain both data and understanding in character and volume of rural traffic;
    - to obtain insight into this character and volume influencing factors;
    - to describe the relationship between volume and influencing factors by means of a mathematical transportation model.
    These objectives are elaborated in chapter 3.

    Chapter 4 deals with the collecting of data and the first elaboration of these data. First the choice is explained of the area for the study of the character and volume of traffic on main and minor roads in a rural area. South-West Friesland, the rural area South of Workum and West of Lemmer, is chosen as the study area (fig. 4.2.1). Important characteristics of this area are:
    - a predominantly rural area, with a few large lakes and some twenty communities, varying from a few hundreds to a few thousands inhabitants;
    - except for farms, few isolated buildings are to be found;
    - a relatively sparse population, with about 16,000 inhabitants on a land area of about 20,000 hectares;
    - mainly agricultural land use (dairy cattle), but also, of old, an important function for recreation (lakes and wooded areas);
    - a relatively sparse but qualitively good road network, of about 12 m/hectare surfaced non-urban roads.

    Section 4.2 deals with a number of these characteristics (tables 4.2.1/7). Attention is paid to developments in the years 1950-1980.

    To obtain insight into the volume of traffic in an area many "instruments" are available. In section 4.3 is explained that for the study in South-West Friesland the following four methods are used:
    - mechanical counts;
    - visual counts;
    - roadside interviews;
    - home and firm questionnaires.

    In section 4.4 for each of the methods is given: the place where and the time during which the collection of data is done; the object of the inventory; how the fieldwork is done and the results - detailed in chapter 5 - as computed from these data.

    The mechanical counts on the roads are realised from 1972 to 1976 on 30 sites. On nearly all sites during one-and-a-half to two-and-a-half years, information is collected (table On 12 sites both daily volumes and hourly volumes were determined.

    In 1973 on the roads both visual counts and roadside interviews were conducted. These two methods could only be made for a random sample (table

    The home and firm questionnaires are spread over the year 1973, on 25 weekdays and 10 days in the weekend, and directed at inhabitants and firms in 6 parts of the study area, the so called cordons (fig. 4.2.2; table

    Section 4.4.6 deals with the question of which relations exist between the different methods. Because the results of the methods differ in time, place and mode only a small overlap occurs. The visual counts and the roadside interviews are mainly used as information extra to the mechanical counts. The home and firm questionnaires do not relate very closely to the other methods, but give insight into character and volume of traffic, and its influencing factors, as demanded in the objectives of this study.

    Chapter 5 deals with traffic characteristics. These are defined in section 5.1 as the ordered, quantitative description of traffic per unit of time. Each characteristic is approached in two ways, namely traffic as produced (or attracted) by inhabitants, and traffic as it appears on the roads. Both approaches show characteristics of the first and the second order. The first order concerns the total amount of trips, the second order the characteristics of trips. This is summarized in the next scheme:

    The summarizing conclusions concerning the traffic characteristics are given in the sections 5.2.4 (for the inhabitants) and 5.3.4 (for the roads).

    It has to be taken into account that traffic is characterised by great fluctuations from day to day. This becomes more evident when the number of "producents" of traffic is smaller. This demonstrates itself especially in data of the home and firm questionnaires, which can only be realised on a restricted number of days, with only a restricted number of households being interviewed each day, because of the manpower available.

    The traffic characteristics of the inhabitants of South-West Friesland are described in section 5.2. The tripproduction, i.e. the average daily trip rate on weekdays, is 2.80, of which 0.94 is by foot, 1.01 by moped and bicycle, 0.51 as driver of a motorvehicle and 0.34 as passenger. In the sections the relationship between different influencing characteristics (like sex and age, income, etc.) and the tripproduction is presented and discussed.

    Between the cordons the largest differences appear for tripproduction by foot, with extremes of 0.21 and 1.21 (table This can be explained by differences in geographical situation. Average daily trip rates for vehicle trips vary from 1.47 to 2.39. This variation can be explained by over- or underrepresentation of social classes with relatively high or low tripproductions. The proportional use of buses and trains depends considerable on their availability within a certain distance.

    The average tripproduction for the area as a whole varies from 2.64 (Mondays) to 3.08 (Tuesdays). This result differs between the cordons: different weekdays are found to have the highest or the lowest traffic volumes of the week. For Saturdays and Sundays the average tripproduction for the area is 1.63 and 1.80 (fig.; large differences occur here also between the cordons.

    The average tripproduction during the months of the year (fig. shows a maximum in June (3.49), followed by a minimum in July (2.45). The cordons differ in this respect too. The results can be influenced by error, due to relatively small numbers of observations per month.

    The traffic during the day shows three peak hours, of which the morning peak in the 9th hour is the highest (fig. The day pattern differs between the cordons in percentages of traffic per hour. Peak hours, however, are similar for the different cordons.

    On average in South-West Friesland about a quarter of the trips are made for 11 work" and "school" (table The distribution by purpose varies widely per cordon. In the "agricultural areas" the proportion of "work traffic" along the roads is relatively low. The proportion of shopping traffic depends a great deal on the geographical situation.

    On an average for South-West Friesland, about 60% of the linked trips occur completely within the cordon where the interviewee is living (table Large differences in the geographical trip character between the cordons are found (fig., as a result of the differences in the available provisions and/or the geographical situation.

    More than half of the trips are shorter than 1 kilometre. The average triplength measured in a bee-line is 4.3 km (table This result varies with the cordon, partly resulting from the composition of the tripproduction by mode.

    Mean trip-duration is 13 minutes (table Differences between the cordons can reasonably well be explained by differences in the geographical situation.

    Tripproduction with a vehicle in South-West Friesland is low in comparison with the results of other Dutch studies. This can be explained by the less dominant commuter traffic, by the presence of many relatively older people, by an average lower income and by a low car ownership. The proportion of public transport in tripproduction in South-West Friesland is lower than in large cities, but higher than in medium sized towns. It is above the national average. School traffic has an important place in South-West Friesland, and is characterised by a relatively high proportion of public transport. The mean travelling time in South-West Friesland is 34 minutes per person per day; this is only half of the 67 minutes which was found to be the national average in 1975.

    The traffic characteristics for the roads (c.q. sites) are described in section 5.3. The great variation in volume is remarkable: the AADT varies in 1973 from 167 to 2606 (table On an average per year, the busiest site on weekdays is 14 times as busy as the quietest site, on Saturdays 19 times and on Sundays 17 times. On all sites the successive weekdays differ from the weekday-average (AADTw) by at most 10%: the extremes are 90 and 108%. The year-averages for the Saturdays on the different sites show greater differences, with extremes of 77 and 134%. For the Sundays the differences are greatest: 78 and 202% (table

    July is on weekdays, for all sites, the month with the highest average volume. This volume however, expressed in percentages of the AADTw, varies greatly from site to site. This is also true for the average volume in the quietest month. Lowest average volume per month appears in different months.

    From figure it is clear that, for the roads, different curves for the highest daily volumes are found. Figure shows that the same applies for hourly volumes.

    The traffic volumes during the day are characterised by a growth from the 6th until the 12th hour. After a slight decrease in the 13th hour a further increase appears until the peak hour is reached, mostly in the 17th hour (fig. On the basis of the year-average the sites can be divided in two groups. The daily peak percentage (expressed in percentages of the daily volume) varies more on the quiet sites. This percentage is in this group on a somewhat higher level than on the busy sites.

    The traffic composition is a traffic characteristic which differs considerable from site to site. The proportion of cars varies on 25 sites on weekdays from 59 to 95%, the proportion of bicycles from 5 to 49% and the proportion of mopeds from 4 to 16% (expressed in percentages of the total number of motorvehicles).

    A great variation can also be found for trip purposes (fig., especially for the proportion of recreational traffic. This varies from 9 to 53%, with an average of 34%. For private as well as for business traffic an average proportion is found of one-third (table

    The results of the geographical trip character related to South-West Friesland and to the surrounding cordon vary from site tot site, because these results depend greatly upon the situation of the site (figures

    The trip distances on the roads relate strongly with the trip purposes at the same place (table The median values for private, business and recreational traffic are respectively 10, 9 and 19 km.

    For the car occupancy,i.e. the number of persons per car, as well, there is a strong relationship with the trip purposes (fig. The number of persons per car varies from 1.70 to 3.22, the weekday average is 2.39.

    The sphere of influence for driving for pleasure differs with the site of the interview (fig. The sphere of influence of the marked tourist route ("Friese Merenroute"), however, is on different roads always in the same order: it varies from 70 to 100 km (fig.

    The average traffic volumes on the roads in South-West Friesland are lower than elsewhere in The Netherlands on comparable roads. Comparing the literature in South-West Friesland a stronger seasonal fluctuation is found. A relation with the recreational function of the area seems logical. This is confirmed by an increasing volume at the weekend, especially on Sundays, on most sites. The rural roads in South-West Friesland are characterised by a low proportion of slow traffic, especially in the summer months and mainly on Sundays. For the trip purposes lower percentages of commuter and business traffic are found, and a relatively high percentage of recreational traffic.

    After the description of the results per characteristic, a comparison is made between the results of the home and firm questionnaire by the inhabitants and the results of the mechanical counts on the roads (section 5.4). It has to be concluded that the comparison is a very difficult one, because of two factors. On one hand a great part of the linked trips of the inhabitants occur within the cordons, so that no mechanical counting site will be passed. On the other hand, three quarters of the traffic on the mechanical counting sites around the cordons is through traffic, without any relation to the inhabitants of the cordons.

    For the traffic volumes by day of the week (table, and by month of the year (table, differences appear between the "inhabitant pattern" and the "road pattern". It seems to be logical that the difference is caused by recreants not included in the home and firm questionnaire.

    The traffic volumes during the hours of the day show also differences between both patterns. It seems logical that this is caused by business traffic, which is only found in the mechanical counts on the roads but not in the home and firm questionnaire by the inhabitants. During the afternoon the recreational traffic can also be an important source of differences.

    Chapter 6 deals with the development of a transportation model, by which link loads (daily volumes) for a road network in a rural area can be calculated from explanatory variables (e.g. inhabitants and jobs). The first steps for the development of a model for rural traffic are derived from the type of models as practised for urban areas and main roads. This study deals with a model for the number of motorvehicles on weekdays, whereby the main item of the mechanical counts, the AADTw, is calculated. The transportation model is divided into four phases:

    The successive phases are the determination of the road network, of the trip generation, of the trip distribution and of the assignment, in a sequential model.

    In constructing the model, part of the data, collected in 1973, are used for the calibration of the phases of the model, and another part of the data for testing the model. This is explained in the next scheme:

    Because the calculations in the transportation model are based on traffic attracting and producing zones, first the area has to be zoned. Therefore a grid-system with variable areas is chosen, in which every village with the surrounding rural area forms a separate zone. This produces 28 zones and four external zones (fig. 6.3.1).

    The road network is described by a network consisting of links limited by nodes. This means a simplification with respect to the real network (fig. 6.3.2). The distance of the links is expressed in minutes of travelling time, calculated from the length of the link and the estimated travelling speed. A number of nodes functions as a centroid, hence all trips that start and finish in the belonging zone, are put in the road network.

    In the road network, the routes and the distances (taken together in the term paths) are calculated between the zones. Restriction of the model to 0-paths (shortest paths) does not suffice in a rural road network, where between many couples of zones more routes of similar distance can be chosen. Therefore first and second paths must be calculated as well. This calculation is restricted to paths which are at maximum 35% longer than the 0-path, while a specific node may appear only once in the same path. The calculation time and the computer memory needed for this procedure is considerable (table 6.3.4).

    In the scope of a transportation model tripproduction is defined as the number of departures per zone per day. The motives for this choice are given in section The complement of the tripproduction is the tripattraction, i.e. the number of arrivals per zone per day. Calculated for a day tripproduction and tripattraction are equal. Tripproduction and tripattraction are taken together in the term trip generation. Only cordon passing trips on weekdays, made as driver of a motorvehicle, are taken into account.

    The relation between the trip generation and the explanatory variables is given in mathematical formulae. These are qua techniques based on regression-analysis (formula The data of the trip generation and the explanatory variables from the cordons are available as input for the regression-analysis. Depending on whether the trip generation of a zone, or the number of trips per household, or per person, is the dependent variable, the terms regression on a zonal basis, on household basis or on personal basis are used. Regression on household or on personal basis are recommended in the literature, because regression models of the zonal type depend strongly on the form and structure of the zones, and thus of the division in zones. Besides, the variation within the zones (which is not taken into account in a zonal model) is much greater than the variation between the zones (table

    Explanatory variables are selected from land use and population characteristics. Explanatory variables with an acceptable value for R-square are not available inside the group of population characteristics, neither for the regression model on household basis (table, nor for that on personal basis (table Preference is given to the number of inhabitants (I) as an explanatory variable for the number of arrivals (A) and departures (V) per zone:
    V = A = 0.474 I (formula

    This is confirmed with respect to the acceptable values for R-square and for the F-test (table This implies that a choice is made for regression on zonal basis and for an explanatory variable from the group of land use.

    Because of the volume of recreational traffic in the study area, this traffic has to be introduced in the trip generation model. This implies that the number of arrivals on an average weekday has to be estimated for those recreational objects with considerable impact on road traffic volume (table It can be concluded from the summarizing table that for nearly all zones a special contribution of recreation to the trip generation has to be taken in account. The number of arrivals of recreational traffic is on an average one-fifth of the number "normal" arrivals, calculated by formula ( In order to make a more reliable introduction of recreational traffic three extra zones are added.

    In the trip distribution model the number of trips between each two zones is calculated (the so called relation pattern) on the basis of the trip generation determined during the foregoing phase.
    For the distribution the gravity model is used. The basis formula is (

    In order to achieve equality between the number of trips distributed from a zone and its tripproduction, and those distributed to a zone and its tripattraction, two so called constraints are added to the gravity model (formulae The coefficients are determined by iteration (formulae The effects of the iteration are illustrated in table

    Attention is paid to the distribution function in the gravity model in section 6.5.3. After the analysis of the exponential function, this one is rejected. In the final model the power function (formula is included.

    The unknown parameter in the power function is estimated in such a way that the 0-D-table calculated by the model coincides as accurately as possible with the 0-D-table observed for the cordons with the home and firm questionnaire. The results of the regression calculations (R-square and the coefficient b1, see table and figures show a moderate agreement between both 0-D-tables. More or less the same results are found for a wide range (2.0-2.5) of values for the parameter. On this basis the value 2.3 is chosen for the parameter of the power function. For the sake of completeness, a calibration is executed, not including the recreational traffic in the trip generation model. As may be expected, the agreement between the observations and the calculations is less satisfactory (figures

    The assignment of the calculated volumes on the road network is the latest phase in the construction of the transportation model. This involves the determination of the routes in the road network, along which the trips, as calculated in the distribution, are made. The assignment results in the calculation of link loads. In this phase, no special observation data are available for calibration. Therefore a choice is made on the basis of study of literature. The most simple assignment model is based on the "all-or-nothing" method, whereby all traffic is assigned to the shortest route. The Kirchhoff-analogy (formula is thought to be the most realistic method for the assignment if more than one route is available. After the completion of the calculations of the assignment phase, it appeared that for nearly two-thirds of the existing relations all traffic is assigned to the shortest path (table

    In section 6.7 the results of the complete transportation model for South- West Friesland are presented. The test with the observations during 1973 is the main item of this section. The most important test is the comparison of the mechanical counts with the calculated link loads (numbers of motorvehicles and vehicle kilometres per weekday). In addition for a number of roads relation patterns and cumulative triplength patterns are also utilised for testing.

    On average the link loads calculated in the model agree to a considerable extent with the mechanical counts:

    There is some overestimation by the model of busy roads and some underestimation of quiet roads (figure and table 6.7.1).

    For roads where a roadside interview was held, the relation pattern of the adjacent cordon as determined by the roadside interview is compared with the relation pattern for that road calculated by the transportation model (table 6.7.3). When the number of relations is not too small, the agreement is often very good; although on some roads, for some relations large differences between model and interview occur. For the sites on the boundary of the study area, the agreement is also reasonably good (table 6.7.4).

    For a number of roads, the cumulative trip-length pattern as calculated with the model can be compared with the cumulative trip-length pattern of the roadside interview (fig. 6.7.2). Due to the calculation method of the model, this comparison has to be restricted to trips inside the study area. Therefore comparison is not possible for trips longer than 15 to 20 km, and the comparison cannot be executed for sites on the boundary of the study area. When these restrictions are taken into account, the agreement is often reasonably good.

    In chapter 7 some items are further commented on, in the form of remarks regarding possible additions or improvements to the reported study.

    Concerning the mechanical counts it is recommended that self-registering counters are used as much as possible, using modified equipment.

    Concerning the home and firm questionnaire it is recommended that the number of addresses per day be increased and that the possession of a drivers licence is registered.

    A tentative study of the development of the traffic volume on three sites in South-West Friesland, shows an average traffic growth of 44% during the period 1973-1983. The growth has been greater on weekdays than on weekend days. For the development of the traffic pattern of the inhabitants, no observations for South-West Friesland are available. Data on Dutch scale give no reason to believe that drastic changes have occurred since 1973 in South-West Friesland.

    Concerning the transportation model, four recommendations are made. More observation data should be made available for the zonal regression-analysis for the trip generation model. More attention should be given to the determination of the relation pattern, which is used for the calibration in the distribution model. Bicycle traffic deserves a place in the model. A better basis for the recreational traffic in the trip generation model has to be developed.

    Recreanten op de Zuid-West Veluwe; onderzoek met behulp van verkeerstellingen en enquetes naar het actuele gedrag van dag- en verblijfsrecreanten
    Bongers, J. ; Tammeling, J. ; Tetteroo, J. - \ 1983
    Wageningen : L.H. - 108
    budgetten - tellen - dichtheid - recreatieonderzoek - openluchtrecreatie - recreatie - onderzoek - wegtransport - tijd - verkeer - nederland - gelderland - veluwe - budgets - counting - density - leisure research - outdoor recreation - recreation - research - road transport - time - traffic - netherlands - gelderland - veluwe
    Verslag van een onderzoek met behulp van verkeerstellingen en enquetes naar het aktuele gedrag van dag- en verblijfsrekreanten in de natuurgebieden op de Veluwe. De waarnemingen zijn verricht op een aantal wegen en fietspaden in de periode van 1980 tot en met 1982 op het zuidelijk deel van de Veluwe
    Modelonderzoek plattelandsverkeer : modelbouw aan de hand van het proefgebied Midden-Brabant
    Heijden, T.G.C. van der - \ 1982
    Wageningen : I.C.W. (Nota / Instituut voor Cultuurtechniek en Waterhuishouding no. 1372) - 47
    tellen - dichtheid - wegtransport - verkeer - nederland - noord-brabant - counting - density - road transport - traffic - netherlands - noord-brabant
    Verslag van de verkeerstellingen op het Dreijencomplex te Wageningen
    Kranenburg, C.W. - \ 1982
    Wageningen : LH - 46
    capaciteit - tellen - dichtheid - onderzoek - wegtransport - verkeer - verkeerspatronen - nederland - gelderland - veluwe - capacity - counting - density - research - road transport - traffic - traffic patterns - netherlands - gelderland - veluwe
    Gunstige perioden voor de bepaling van het jsarlijks etmaalgemiddelde door mechanische verkeerstellingen
    Kranenburg, C.W. - \ 1982
    Wageningen : Landbouwhogeschool - 59
    tellen - dichtheid - meting - methodologie - nederland - fysica - wegtransport - verkeer - counting - density - measurement - methodology - netherlands - physics - road transport - traffic
    Verkeersverloop in een aantal boswachterijen : periode 1964 tot 1979
    Bakker, J.G. - \ 1981
    Wageningen : I.C.W. (Nota / Instituut voor Cultuurtechniek en Waterhuishouding no. 1230, 1284) - 2
    tellen - dichtheid - ondernemingen - bosbeheer - bosbedrijfsvoering - bosbouw - nederland - recreatie - wegtransport - verkeer - counting - density - enterprises - forest administration - forest management - forestry - netherlands - recreation - road transport - traffic
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