Travel time reliability analysis of three different routes in baghdad city

Transportation is an important aspect of the daily life allowing people to participate in human activities and to obtain basic needs. The rise in population has resulted in an escalation in transportation requirements, leading to an augmented volume of traffic on the roads. Consequently, mobility-related predicaments, such as congestion, have become more prevalent, particularly in city centers where human activities are concentrated. With that sense, transportation networks are to be planned properly to control urban traffic to mitigate mobility problems related to transportation travel time. Travel time reliability refers to the level of assurance and consistency with which travel times can be predicted on a given transportation system. A reliable transportation system offers a certain level of guarantee that one can reach their intended destination within a reasonable timeframe. A transportation system that lacks reliability is susceptible to unforeseen delays, resulting in higher expenses for its users. Travel time reliability is a metric that evaluates the consistency of time taken to traverse a particular link or segment of a road during various hours of the day, quantified in terms of additional time (buffer) that drivers must allocate to compensate for unexpected delays. Travel time reliability is a crucial measure not only for transportation providers but also for passengers who rely on the system for their daily commuting needs. In this study data collection process began when the test vehicle was equipped with GPS (moving vehicle technology) to collect data on specified paths. The Statistical Package for the Social Sciences (SPSS) program was utilized to analyze GPS field data collected from 50 running trials conducted in both the South and North directions during morning and evening hours. The aim was to assess the impact of increased traffic volume on flow behavior of the vehicles and reliability in three selected routes. In the first case, the average travel time for all links in three paths was obtained from the real time GPS vehicle data. After that traffic volumes on each path were estimated using the BPR equation. Following, a simulation was conducted using the PTV Vissim program to increase traffic volumes by 10% for each iteration up to 10 times, and the average travel times for all increments were calculated. The purpose was to compare the simulation results with the initial and realistic case to determine the traffic structure and reliability after the proposed changes. The results of the buffer time index for three routes (real case), Route1, Route2, and Route3, were obtained as 22%, 12%, and 14%, respectively. In the simulation case, the results for Route1, Route2, and Route3 were obtained as 7%, 8%, and 9%, respectively. These results showed that the reliability got better for Route1 during the peak period, and the best values in real case was for Route2, and in simulation case for Route1. Extra delay in the real case over the free flow travel time was observed on Route1, Route2, and Route3 in terms of the 95th percentile travel time for the real case, which were 52%, 38%, and 41%, respectively. While in the simulation case, the delays increased to 67%, 42%, and 50% for Route1, Route2, and Route3 after the last iteration, respectively.