Car-Following Interaction and the Definition of Free-Moving Vehicles on Two-Lane Rural Highways

Al-Kaisy, Ahmed; Karjala, Sarah

doi:10.1061/(asce)te.1943-5436.0000148

Cited by 34 publications

(17 citation statements)

References 9 publications

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“…An experience on Swedish roads reveals that vehicles could be considered free beyond 6 s headway when interaction of vehicles is usually observed to be nonexistent [20]. Similar results were also obtained by couple of studies conducted on two-lane roads [21,22]. Dey and Chandra [23] proposed two continuous statistical distribution models, gamma and lognormal for desired time gap and time headway of drivers in a steady car-following state on two-lane roads under mixed traffic conditions.…”

Section: Research Motivationssupporting

confidence: 59%

Headway distribution models of two-lane roads under mixed traffic conditions: a case study from India

Roy

Saha

2017

Eur. Transp. Res. Rev.

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Introduction The time headway of vehicles is of fundamental importance in traffic engineering applications like capacity, levelof-service and safety studies. Further, the performance of traffic simulation depends on inputs into the simulation process and 'accurate vehicle generation' is critical in this context. Thus, it is important to define headway distribution pattern for the purpose of analyzing traffic and subsequently, taking infrastructure related decisions. In so far, majority of the researches on this subject are based on homogeneous traffic and effects of mixed traffic especially on two-lane roads are yet to be culminated. The present study, thus, aimed at investigating headway distributions on such roads under mixed traffic situation. Methods Field study was conducted on two-lane highways in India that exhibits heterogeneity in its traffic composition. Contestant headway distribution models were evaluated and four distribution functions namely, log-logistic, lognormal, Pearson 5 and Pearson 6 were considered while modeling the headway data. The appropriate models were selected using a methodology based on K-S test and subsequent field validation. Results Log-logistic distribution was found appropriate at moderate flow whereas, at congested state of flow it was Pearson 5. However, at unstable flow nearing capacity, both, following and non-following components of headways were observed to follow different distributional characteristics. Nomographs are developed for calculating the headway probabilities at different flow levels considering the appropriate distribution models. 'Probability of headway less than't's' increases with the flow rate and rate of such increase is considerably high for headways 7.5 s or more. This attributes to the fact that at heavy flow more vehicles are entrapped inside platoons and they move in following with shorter headways. Further, a comparison was made between the headway probabilities obtained in the current study and road segments that exhibit more or less homogeneous traffic. It was found that at moderate flow level proportion of shorter headways are considerably high under mixed traffic. Conclusions The present paper demonstrates the effect of mixed traffic on distribution of time headways of two-lane roads. Presence of slower vehicles in such traffic leads to frequent formation of platoons, thereby, increases the risk taking behavior of drivers' while overtaking. As a result, proportion of shorter headways increases resulting in highly skewed observations. Thus, the study proposed Log-logistic distribution under medium flow since it can model events which have 'increased initial rate' and Pearson 5 under heavy flow to model 'highly skewed data'. The model outputs were accordingly compared with other studies and were found to explain the mixed traffic characteristics satisfactorily. The present study, thus, creates a starting point of further initiatives aimed at establishing a robust method of modeling headways on two-lane roads with mixed traffic.

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Section: Research Motivationssupporting

confidence: 59%

Headway distribution models of two-lane roads under mixed traffic conditions: a case study from India

Roy

Saha

2017

Eur. Transp. Res. Rev.

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“…The study found that the speed of two successive vehicles are linearly dependent on time headway for headways up to 6 seconds. A similar finding has been reported in a few other studies (Al-kaisy & Karjala [17], Lobo et al [18], Hoogendoorn [19]). Some other studies have reported the use of 5 seconds as the headway cut-off value for identifying free-flowing vehicles in the traffic stream [20][21][22][23][24].…”

Section: Introductionsupporting

confidence: 91%

Untitled

2019

CERJ

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This paper presents an empirical investigation into car following interactions. Detector data from 15 study sites in Idaho, Montana and Oregon representing all three highway classes were used in this investigation. Investigation of speeds and headways suggests that the headway at which vehicles start the car-following interaction (referred to in this study as the critical headway) varied in a range that is site-specific, with the lower limit generally varying between 1 and 2 seconds, and the upper limit varying between 6 and 7 seconds. The study also found that vehicles traveling at a perceived minimum safe headway increase in number as headways get smaller and more vehicles enter the car following state. Further, the study introduced a new approach for estimating percent followers in the traffic stream and used field data in deriving headway cut-off values. Headway cut-off value for percent followers at class I sites varied between 1.8 and 2.8 seconds, while those for class II and class III sites are slightly above 3 seconds.

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“…A headway value longer than 6 s was considered as the criterion to determine unimpeded speeds, based on the analysis of speeds from field data. This threshold was also suggested based on empirical observations .…”

Section: Methodsmentioning

confidence: 99%

Modification of the Highway Capacity Manual two‐lane highway analysis procedure for Spanish conditions

Moreno

Llorca

Washburn

et al. 2016

J of Advced Transportation

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SUMMARYThe US Highway Capacity Manual (HCM) methodology is used in Spain to evaluate traffic operation and quality of service. The effect of passing manoeuvre on two-lane highway operational performance is considered through adjustment factors to average travel speeds and percent time spent following. The procedure is largely based on simulations in TWOPAS and passing behaviours observed during US calibrations in the 1970s. It is not clear whether US driving behaviour and vehicles' performance are comparable with Spanish conditions. The objective of this research is to adapt the HCM 2010 methodology to Spanish driver behaviour, for base conditions (i.e. no passing restrictions). To do so, TWOPAS was calibrated and validated based on current Spanish passing field data. The calibration used a genetic algorithm. The case study included an ideal two-lane highway with varying directional traffic flow rate, directional split and percentage of trucks. The updated methodology for base conditions is simpler than the current HCM 2010 and does not rely on interpolation from tables.

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Car-Following Interaction and the Definition of Free-Moving Vehicles on Two-Lane Rural Highways

Cited by 34 publications

References 9 publications

Headway distribution models of two-lane roads under mixed traffic conditions: a case study from India

Headway distribution models of two-lane roads under mixed traffic conditions: a case study from India

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Modification of the Highway Capacity Manual two‐lane highway analysis procedure for Spanish conditions

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