Abstract:
Analysis and interpretation of traffic Operations on national highways reqUIre a sound
understanding of the traffic flow parameters. Such traffic flow parameters are traffic arrival
headways, free speed of vehicles, operating speed and speed-flow-density relationship. No
significant study has yet been made to investigate these traffic parameters of Bangladeshi
national highways. In this study, effort has been given to investigate the traffic arrival pattern
and free speed characteristics of vehicles on two-lane two-way national highways of
Bangladesh. The research study has been based on field data. Both video and manual data on
the traffic flow of selected national highways have been collected for a net period of
approximately twenty five hours. The analysis of collected data has been made using different
statistical softwares. Analysis of traffic arrival pattern using the vehicular time headway data
has revealed that the pattern follows more than one statistical distribution models for all the
highways. Generally, it has been observed that the vehicles maintain close head ways when
they are in following situation. It has been observed that the traffic arrival pattern on selected
Bangladeshi national highways can be described by one or more of the two statistical
distributions, namely, exponential and lognormal. The relevant parameters of the
corresponding arrival headway distributions have been estimated. Analysis of free speed data
of vehicles on a typical section of Dhaka-Aricha highway has revealed that the free speed of
the commonly found vehicles(bus, minibus, truck, passenger-car, nonmotorised vehicles)
follow normal distribution pattern. Corresponding parameters of the normal distribution have
also been estimated. From regression analysis, it has been found that free speed of vehicles
depends on the pavement and shoulder width. In a pavement width range of 5.8m to 7.5m,
free speed of commonly found motorised vehicles increases in a range of 7.25 kmph to 10.29
km/ph for each metre of pavement widening for flat, straight and disturbance free highway
section. The analysis has also revealed that free speed of vehicles increases with the increase
in shoulder width except for the case of bus(the reason of which has been identified as a local
phenomenon on a particular highway).
