Available online at www.sciencedirect.com ScienceDirect Transportation Research Procedia 17 ( 2016 ) 428 – 437 11th Transportation Planning and Implementation Methodologies for Developing Countries, TPMDC 2014, 10-12 December 2014, Mumbai, India Study on Speed and Time-headway Distributions on Two-lane Bidirectional Road in Heterogeneous Traffic Condition Akhilesh Kumar Mauryaa*, Sanhita Dasb, Shreya Deyb, Suresh Namab aAssociate Professor, Department of Civil Engineering, Indian Institute of Technology Guwahati, Guwahati, Assam,781039, India. bPost Graduate Students, Department of Civil Engineering, Indian Institute of Technology Guwahati, Guwahati, Assam,781039, India Abstract In the present paper an attempt has been made to have an idea about speed and headway distribution pattern in heterogeneous traffic condition comprising of various motorized and non-motorized vehicles having widely varying speed range. Distribution of speed and time headway has been studied for different density levels namely, 0-20 PCU/km, 20-40 PCU/km, 40-60 PCU/km and 60-80 PCU/km. Statistical validity of each distribution is evaluated by Kolmogorov-Smirnov (K-S) test. Results show that the speed and time headway follow different distribution patterns under different density levels. Moreover speed distribution profile is evaluated for different types of vehicle and time headway distribution profiles are also determined for different vehicle pairs. The findings can be used for developing simulation models for two-way, two-lane roads under heterogeneous conditions. © 20162015 The The Authors. Authors. Published Published by Elsevierby Elsevier B.V. B.This V. is an open access article under the CC BY-NC-ND license (Selectionhttp://creativecommons.org/licenses/by-nc-nd/4.0/ and peer-review under responsibility). of the Department of Civil Engineering, Indian Institute of Technology Bombay. Peer-review under responsibility of the Department of Civil Engineering, Indian Institute of Technology Bombay Keywords: Speed distribution; Headway distribution; Heterogeneous traffic; Bi-directional road 1. Introduction In developing countries like India, traffic conditions are highly heterogeneous comprising vehicles of varying physical dimensions, axle configurations, weight, power-to-weight ratio and other dynamic characteristics such as braking power, acceleration, etc. Due to these characteristics, the vehicles do not follow lane discipline, and occupy any lateral position along the entire width of the roadway irrespective of lane markings. Studies on speed and time headway distributions of road traffic are important as the statistics provide a deeper insight into the aggregate behavior of vehicles and drivers. Speed is one of the most important fundamental parameters to describe the performance of any roadway system. Knowledge of speed and time-headway is very important and essential in traffic engineering as development of a good transportation system is completely dependent on it. It plays important role in many areas, starting from geometric design of road, speed is required in accident studies, regulation and control of traffic * Corresponding author. Tel.: +91-361-258 2426; fax: +91-361-258 2440. E-mail address: [email protected] 2352-1465 © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Department of Civil Engineering, Indian Institute of Technology Bombay doi: 10.1016/j.trpro.2016.11.084 Akhilesh Kumar Maurya et al. / Transportation Research Procedia 17 ( 2016 ) 428 – 437 429 operations, ascertaining travel time, determining capacity, delay and queue analysis, level of service analysis etc. Knowing speed distribution is necessary to fix a proper posted speed limit in order to facilitate safe and efficient movement of drivers. Time headway is a fundamental microscopic parameter in traffic flow theories that is measured by the difference in the time interval between two successive vehicles as they pass a reference point on the roadway measured from the same common features of both the vehicles. But under mixed traffic condition definition of headway is modified as the time interval between two successive vehicles as they pass a reference line on the entire width of the roadway. If the traffic is more or less homogeneous, it is possible to predict the distribution from the previous available researches but when there is great variation in speed of slow and fast moving vehicles it does not always follow conventional distributions. Again three-wheeler rickshaw and motor cycle are having high maneuverability, so they creep through the gap between bigger vehicles and retard the free movement of them. They do not follow lane discipline even if there are proper lane markings. Again there are various types of car having different length, width, maneuverability and acceleration-deceleration capability. All these circumstances make the traffic condition very complex. The present paper attempts to study the speed and time-headway distribution under such conditions in a two-lane both way urban road stretch. 2. Literature Review A number of literatures are available explaining speed distribution pattern in homogeneous traffic condition but still there are only a few demonstrated the distribution pattern under heterogeneous traffic. Zhang and Maher (1998) used normal distribution in the simulation study and lognormal distribution in the application of the matching-Furness method to estimate the real data trip matrix with platoon dispersion. Dixon et al. (1999) examined speed data in 12 sections in rural multilane highway and concluded the distribution of free flow speed was found to be normally distributed. Jungwook (2008) suggested that on certain roadway systems Gaussian mixture model using the EM algorithm could be used to properly characterize the severity and variability in speed distribution due to congestion under mixed traffic condition in interstate freeway. Hasim et al. (2011) carried out his study on two lane rural highway in Egypt and on conducting Kolmogorov–Smirnov one-sample test (1-sample K–S test) he found that the speed data were normally distributed. Filippo and Marinella (2011) studied low volume roads in Italy and observed that speeds are normally distributed. Zou and Zhang (2011) said that a single normal distribution cannot accurately accommodate the excess kurtosis present in the speed distribution and they proposed skew-normal and skew-t distribution to fit speed data. They suggested that these two distributions can be applied effectively for both homogeneous and heterogeneous traffic. Sacchi et al. (2012) developed a new operating speed model to predict speed in urban arterial and collector street and found that speed data in all sites are normally distributed. Wang et al. (2012) introduced truncated normal and lognormal distribution for modeling speeds and travel time. Chandra et al. (2013) conducted study on multilane divided urban road under mixed traffic condition and concluded that speed distribution will follow normal distribution if SSR (Speed Spread ratio) is between 0.86-1.11. Hastim and Ramli (2013) have studied speed distribution in two lane and four lane oneway road on heterogeneous traffic in Makassar, Indonesia and found that at few roads satisfy normality tests while rest sections failed in the same. In the field of time headway analysis, many authors gave their contribution on the development of a headway model and analysis of some statistical properties of time headway. Starting from Adams (1936) who formulated the idea of arrival as a Poisson process, he concluded that the negative exponential distribution would be the best fit for time headway distribution. Dawson and Chimni (1968) proposed Hyperlang model as a linear combination of a translated exponential function and translated Erlang function. Tolle (1971) concluded that the lognormal distribution provided good fit for the traffic in platoons. Cowan (1975) proposed four headway models, M1, M2, M3 and M4 yielding Poisson process, shifted exponential distribution, mixed and exponential distribution, and generalized M3 distribution respectively. Griffiths and Hunt (1991) considered double displayed negative exponential distribution as an appropriate distribution for modeling the vehicular headways in urban areas. Hossain and Iqbal (1999) reported that the headways followed exponential and lognormal distribution for the vehicles in Dhaka. Under homogeneous conditions, Al-Ghamdi (2001) suggested that negative exponential distribution fitted well for flow rate less than 400 veh/h, shifted exponential and gamma distribution for medium flows i.e. 400-1200 veh/h and Erlang distribution for high flows above 1200 veh/h. Chandra and Kumar (2001) reported hyperlang distribution as the best distribution to describe headways on urban roads under mixed traffic. Zhang (2007) reported that Doubly Displaced negative exponential distribution (DDNED) fitted well for flow levels of 400 veh/h and 1,400 veh/h. Riccardo and Massimiliano (2012) found that Inverse Weibull distribution fitted well for most flow rates ranges and Log Logistic, 430 Akhilesh Kumar Maurya et al. / Transportation Research Procedia 17 ( 2016 ) 428 – 437 Person 5 fitted well for high flow rates on two lane two way roads in the Province of Venice. Dubey et al. (2013) reported Weibull + Lognormal (WLN) and Weibull + Extreme value (WEV) models as the best mixture models