Pritam Saha

Evaluation of speed–flow characteristics on two-lane highways with mixed traffic

AbstractThe HCM (Highway Capacity Manual 2010) classifies two-lane rural highway that passes through developed areas as ‘Class III’ and suggests using Percent Free-Flow Speed (PFFS) as performance measure to define Level Of Service (LOS). Apparently, this performance measure addresses the main limitation associated with using Average Travel Speed (ATS) as a measure of performance. However, larger speed differential under heterogeneous traffic causes error in estimating Free-Flow Speed (FFS) and thus affects PFFS. This implication was examined in the present study using field data collected on a national highway approaching a city. Speed–flow equations were developed and intercept values were compared to the FFS obtained according to HCM guidelines. Comparison confirms a very close agreement between average FFS value and those obtained for different types of vehicle separately except for car. This consequently causes an error in estimating PFFS since the traffic composition consists of significant proporti...

Application of Principal Component Analysis for Outlier Detection in Heterogeneous Traffic Data

Level-of-service (LOS) measures of two-lane highways exhibit incompatibility if the prevailing traffic is heterogeneous in character. Thus, such traffic warrants development of LOS criteria on the basis of compatible measures which capture its characteristics. The present paper has suggested the use of percent speed-reduction and percent slower vehicles, as the measures of performance, while defining LOS criteria. Defining such criteria is basically a classification problem and clustering could be applied as an effective technique for its solution. However, heterogeneity in the traffic mix results in the presence of significant proportion of outliers in the data set, which can distort the results and render into misleading or useless outcomes. The study considers principal component analysis to be an efficient technique in detecting outliers from the data set and accordingly applies it on the proposed LOS measures. An iterative process, adopted for removing outliers, indicates that significant proportion of outliers comprises of non-motorized traffic data; this accordingly ensures reliability of the data set. The study concluded the unfeasibility of LOS assessment of the entire traffic, considering both motorized and non-motorized modes, with respect to a common scale.

Preferred time headway of drivers on two-lane highways with heterogeneous traffic

Abstract This paper presents an investigation on the adequacy of one of the major performance indicators for two-lane highways, the percent-time-spent-following (PTSF) under changing driver’s behavior in choosing headways. Field study was conducted on a two-lane highway in India that exhibits heterogeneity in its traffic composition and a wide range of flow levels was covered while collecting data. The appropriate headway distributions were selected based on goodness-of-fit test. Exponential or Erlang distributions exhibit their aptness in describing headways up to a volume to capacity ratio of 0.3 and gamma and exponential distributions were compatible for headway data corresponding to a volume to capacity ratio of 0.4 and above. Around 40% drivers were observed to adopt headways 2 s or less at heavy flow when a car-following situation prevails; these headways are considered unsafe in several instances. Further, speed–headway relationships were established to assess a headway threshold beyond which vehicles could be considered free. Empirical investigation indicates a value of about 6 s under such traffic unlike 3 s as considered in PTSF estimation. Another major implication on PTSF is a few drivers move in a platoon by choice even if they have a gap of more than 6 s and passing opportunities.

Pedestrian Flow Characteristics at Signalized Intersections in Mixed Traffic Situations: A Case Study in Kolkata, India

Abstract This paper focuses on the behaviour of pedestrians when they cross at signalized intersection under mixed traffic situations. Based on a field study at a typical signalized intersection in the commercial hub in the city of Kolkata, the paper describes various characteristics of pedestrian movements. Several attributes like width of the road, age and gender of the pedestrian and if they are carrying any baggage were considered at the time of performing such analysis. The age and gender of pedestrians were found to have an impact on their speeds; however, children were observed to walk faster since they are accompanied by their parents in most occasions. The speed of panic-stricken pedestrians who prefer to run on the zebra marking while crossing the road at intersection was observed to be quite high. Interestingly, the effect of carrying baggage on walking speeds was found to be insignificant at the study site. Accordingly, the current study made an attempt to further investigate the fact by conducting an informal opinion poll. The poll of about 50 road users revealed that since most of them walk towards their office or business centre, they usually carry lighter baggage and quite often they are compelled to walk fast. Further, at crosswalk, speed does not vary to a considerable extent with the increase of flow; this attributes to the absence of confined flow. The observed flow parameters were plotted and the scattered diagrams indicate widespread data points that largely follow the Greenberg’s logarithmic model.

An Empirical Analysis of Time Headways on Two-Lane Roads with Mixed Traffic

This paper demonstrates a method of describing headways of two-lane roads under mixed traffic situation using statistical distributions. Characteristically such distributions may have two forms: single and mixture of two or more distributions. A single distribution, however, cannot describe headways in the event of significant proportion of shorter headways in traffic. Use of mixed models is appropriate in such situation since they describe headways by decomposing them into free and following component. Based on experiences with mixed traffic and field studies on two-lane highways of India, this paper has shown that Cowan’s M3 can be reasonably applied for modeling headways up to a flow level that corresponds to ‘moderate to heavy flow’. However, since shifted negative exponential distribution part of the Cowan’s M3 distribution cannot model short headways, Cowan’s M3 distribution cannot model headway data at congested state of flow when almost all the vehicles in the traffic stream start moving in following.