This Issue 4 of Volume 2 comprises seven papers focusing on the issues of driving behavior and traffic flow in Asia. The first two papers examine the issues of traffic accidents: one looks at the influence of individual attributes of drivers, especially those younger and older drivers (Park et al.), and the other investigates the influence of road surface conditions on driving behavior (Ranjitkar and Nakatsuji). The third and fourth papers investigate the issues of driving speed: the former emphasizing the effects of vehicle attributes (Saifizul et al.) and the latter analyzing the characteristics of free-flow speed (Tseng et al.), while the fifth paper (Narupiti et al.) estimates travel time based on driving speed. The sixth paper (Lin et al.) explores the ability to simulate traffic situation using the refined cellular automaton modeling in both pure and mixed traffic situations. The last paper (Tsukai et al.) explores the effects of different toll discounting policies on traffic flows, which are decomposed into independent components. Each of the components captures different temporal characteristics of traffic flows. Contents and findings of these studies as well as future challenges are summarized below.
In 2009, there were 106 fatalities per 1,000 car accidents on Korean expressways, more than double those of other road types. In terms of accident casualties by age, the fatality rate for older drivers was nearly five times more than other age groups, while the injury rate for younger drivers was almost one and a half times more than other age groups. The casualty rates have shown varying degrees of injury by age. To determine the factors that influence injury severity by age, accident data on Korean expressways for the last five years were analyzed. The results show that, for younger drivers, intentional violations increased injury severity. For older drivers, less physical capability of reaction and drowsiness were identified as factors that increased injury severity. It would help to develop systematic grounds towards formulation of safety policies.
Human factor is a major contributor in road traffic crashes. This paper reports a comparative study of human driving behavior under icy and slippery to dry road surface conditions. Extensive car-following experiments were conducted on a test track in Japan under icy and dry conditions using Real Time Kinematic (RTK) GPS receivers. These experiments replicated various uninterrupted driving conditions in winter and summer seasons. Several speed patterns were tested for the lead vehicle representing various levels of disturbance in the traffic flow. The responses of the following drivers were analyzed based on three important human factors, namely: perception response time, sensitivity factor, and stability factor. The response time was significantly higher in icy conditions compared with dry road surface conditions while the difference in sensitivity factor was not that significant. The stability of the platoon was also analyzed from both the local and asymptotic stability points of view.
This study explores empirically how the gross vehicle weight (GVW) of a following vehicle and the size of leading vehicle will affect the driver behavior in controlling their speed under different compositions of leader-follower pairs in a car-following situation. A large sample of traffic and vehicular data for various vehicle types were obtained continuously using a weigh-in-motion (WIM) based transport data collection system installed at Federal Route 54 in Malaysia. Then, statistical analysis was applied to explore the driver behavior in controlling the speed in a car-following situation from two different perspectives: driver’s visual input and vehicle dynamics capability. The main finding of this study is that when we incorporate the vehicle dynamic’s capability in a car-following situation, the GVW of the following vehicle and the size of the leading vehicle were significant sources of variation in the following vehicle’s speed and relative speed, and their interaction influences the driver behavior in controlling the speed.
The Taiwan Area Highway Capacity Manual of 2001 describes free-flow speed as an input for level-of-service analysis of urban arterials. However, it does not provide a tool for estimating free-flow speeds on urban arterials. To bridge this gap, this study collects free-flow speeds from fourteen urban arterials in three cities of Taiwan. The data were first used to investigate the characteristics of free-flow speed in relation to vehicle type, geometric design, and speed limit. They were then used to develop models for estimating average free-flow speed and to establish the probability distributions of the free-flow speed of individual vehicles. Intersection spacing, speed limit, median type, lane location, and vehicle type are found to have obvious effects on average free-flow speed. The results of this study will be useful in revising the existing methodology for analyzing Taiwan’s urban arterials. They are also useful for calibrating microscopic models for simulating urban traffic flows.
The objective of this paper is to evaluate travel time estimation techniques for off-line and on-line applications using traffic speed. The study area was the 8.1-km Chalerm Mahanakorn Expressway Daokanong - Port section in Bangkok. Traffic speeds were collected at 7 stations. Average traffic volume of 6,140 vph was observed during the 6:00am to 22:00pm period. Four offline methods were used to convert speed into travel time for each link, namely: mid-point, section average, weighted section average, and San Antonio's (lower speed). To aggregate link travel time into route travel time, the instantaneous and time slice methods were considered. The estimated travel time were then compared with the actual travel time observed from 1,632 vehicles. The results indicate that the accuracy depends on the time period and level of traffic congestion. Considering route travel time, the time slice method gives a slightly better accuracy than the instantaneous method. Comparing the offline (all data present) and online (short-term forecast of speed in the next time slice(s)) travel time estimation, the two methods yield similar accuracy. The findings of the research imply that the practical travel time estimation may need several methods suitable for each time period. The improved estimation can increase the accuracy over a single method, thereby decreasing the MAPE from 14-20% to 11%.
Traffic patterns and the associated phase transitions for pure and mixed traffic are explored in this study. Local traffic parameters are defined in a spatiotemporal (3-D) domain so that the cellular automaton (CA) modeling can precisely capture the traffic features. Refined CA simulations are performed under pure and mixed traffic scenarios on a multilane stretch of road where virtual detectors are placed to measure the 3-D traffic parameters. It is found that the proposed measuring techniques with refined CA modeling can copiously explore the local traffic patterns with associated phase transitions in both upstream and downstream of a bottleneck. Finally, a comparison of the local traffic parameters with the global counterparts is also presented.
Recently, various toll policies and social experiments have been conducted for ETC users of Japanese expressways. While the vast number of reports refers to the change of traffic for each section, the influence of toll policies has rarely been evaluated from the statistical viewpoint, due to the lack of an adequate model to deal with the multivariate time series including many peaks. The purpose of this study is to clarify the influence of toll policies on the traffic levels on expressways by using Independent Component Analysis (ICA). The continuously observed traffic data at several different sites on the expressway were decomposed into several independent series by using mixing coefficients (i.e. weight parameters) to convert the independent series into the observed series. ICA isolates the common and stable fluctuations in several traffic series in relation to toll policies. Moreover, the estimated independent series under the different toll policies were statistically compared to clarify whether the significant difference between the independent series occurs, or not.