Tony Z. Qiu

Perspectives on Future Transportation Research: Impact of Intelligent Transportation System Technologies on Next-Generation Transportation Modeling

In this paper, we attempt to summarize the impact of technologies, especially intelligent transportation system (ITS) technologies, on transportation research during the last several decades and provide perspectives on how future transportation research may be affected by the availability and development of new ITS technologies. The intended audience of the paper includes young transportation researchers and professionals. Current transportation models are divided into “generations” based on their technological and practical background. Based on the trends in the past and the potential technologies to be implemented in the future, general characteristics of the next generations of transportation models are proposed and discussed to provide a vision regarding expected future achievements in transportation research. This paper is intended to be a working document, in the sense that it will be updated periodically.

Combining Variable Speed Limits with Ramp Metering for freeway traffic control

This paper proposes a control strategy for combining Variable Speed Limits (VSL) and Ramp Metering (RM) to maximize the flow of a recurrent bottleneck which can be modeled as a lane reduction. The control strategy can be simply described as: (a) Assuming a known ramp metering rate for each onramp; (b) using Finite Time Horizon Model Predictive Control to design VSL for each link; (3) VSL design is based on a simplified 2nd order METANET model with density (or occupancy) and mean speed as the state variables. Simulations are conducted in Matlab with several performance measures to evaluate the control strategy quantitatively.

Variable Speed Limit Control Design for Relieving Congestion Caused by Active Bottlenecks

AbstractVariable speed limit (VSL) can be used on freeways to manage traffic flow with the goal of improving capacity. To achieve this objective, it is necessary that both speed and density dynamics be represented accurately. In this study, to deeply understand the effectiveness of VSL control, an analytical model was developed to represent drivers’ response to updated speed limits and macroscopic speed dynamical change with respect to changeable speed limits. Specifically, to model the freeway links having VSL control, the fundamental diagram (FD) was replaced with the VSL control variable in the relaxation term of the METANET. This modification led to the speed control variable appearing linearly, which is preferable for online computation. The density dynamics are based on the cell transmission model (CTM), which is introduced to estimate the transition flow among successive links with some practical constraints. It also offers flexibility in designing active bottleneck in which there is a capacity dro...

Estimation of Freeway Traffic Density with Loop Detector and Probe Vehicle Data

Density, speed, and flow are the three critical parameters for traffic analysis. High-performance traffic management and control require the estimation–prediction of space mean speed and density for large spatial and temporal coverage. Speed, including spot mean speed and space mean speed, and flow estimation are relatively easy to measure and estimate, while less attention has been devoted to measuring and estimating density. Because IntelliDrive (previously known as vehicle infrastructure integration) is a promising technology for providing a new type of real-time traffic data, and loop detector systems have already been widely deployed, this paper proposes a method to estimate freeway traffic density with both loop detector data and IntelliDrive-based probe vehicle data. The proposed method has been validated with Berkeley Highway Laboratory loop detector data combined with field-collected probe vehicle data in the first validation study and next-generation simulation video trajectory data in the second validation test. The algorithm can be used offline and in real time.

Assessing Mobility and Safety Impacts of a Variable Speed Limit Control Strategy

With the recent advances in active transportation and demand management, variable speed limits (VSLs) have been identified as an active traffic management strategy for improving freeway mobility and safety. Several heuristic VSL strategies have been proposed and evaluated. This paper proposes a model predictive VSL control strategy and evaluates its safety and mobility impacts. The strategy uses second-order traffic flow models to predict the traffic state and to provide a speed for optimizing corridor operational performance. A sensitivity analysis of the VSL update frequency and the safety constraints for the VSL strategy was performed to determine the best scenario in terms of safety and mobility. A stretch of Whitemud Drive, an urban freeway corridor in Edmonton, Alberta, Canada, was selected as the study area. The proposed VSL strategy was implemented in the microsimulation platform with a special software module. A real-time collision prediction model was developed for the same study area by using a matched case-control logistic regression technique to estimate the collision probability for each scenario. The results indicated that the proposed VSL control strategy can improve safety by approximately 50% and mobility by approximately 30%. A VSL update frequency of 5 min and a maximum speed difference of 10 km/h between successive time steps yielded the best performances. This finding can be useful for field implementation of VSL control.

Pedestrian Safety Analysis in Mixed Traffic Conditions Using Video Data

With the dramatic development of image processing technology, a growing number of traffic flow detection and analyses have been conducted by using video data. Time to collision (TTC) and postencroachment time (PET) are two major parameters used to indicate the severity of a potential collision and to capture an imminent vehicular accident. However, microlevel pedestrian-involved collisions are less studied because they are hard to observe or record. This paper tries to extract the traffic object locations from video data, to define the time difference to collision (TDTC) parameter as a variation from TTC and PET to fit the pedestrian-involved potential collisions/conflicts, analyze the interaction behavior between pedestrian and vehicles, and validate the TDTC parameter in indicating pedestrian safety performance by using 100 groups of interaction data. The results show that the interaction cases with larger TDTC values are safer, whereas the cases with continuously closer to zero TDTC values are more dangerous. About 80% of the cases classified by the TDTC parameter have the same result with the independent observation; if TDTC is combined with vehicle speed, the classification result can be improved. More mixed traffic scenes will be conducted based on this research in the future.

Passenger Traffic Characteristics of Service Facilities in Rail Transit Stations of Shanghai

AbstractThe configuration of service facilities, such as ticket vending machines, staffed ticket booths, automatic fare gates, and escalators, is an important issue for the plan and design of rail transit stations. Reasonable configuration of service facilities is based on a good understanding of the passenger traffic characteristics of such service facilities, which are affected by passenger characteristics, station types, and facility performance. To study the passenger traffic characteristics of service facilities, five stations are selected in Shanghai, and their passenger traffic data are collected and analyzed. In this study, the results indicate that service-time frequencies of ticket vending machines and staffed ticket booths follow Weibull distribution and exponential distribution, respectively, and that the headway of passengers passing the automatic fare gate under ideal conditions follows normal distribution. According to the service time and headway distributions of ticket-selling facilities ...

Effect of Circadian Rhythms and Driving Duration on Fatigue Level and Driving Performance of Professional Drivers

Circadian rhythms, inherent in all humans, consist of 24-h biological patterns that affect a persons fatigue level. The effect of circadian rhythms on driving performance was explored in an on-road driving study. Fifteen middle-aged professional daytime drivers were recruited to participate in the experiment. Participants were classified into three groups: (a) a morning group that started driving at 09:00, (b) a noon group that started driving at 12:00, and (c) an evening group that started driving at 21:00. Each group completed a 6-h driving task. The self-reported Karolinska sleepiness scale score was recorded every 5 min, and data on driving performance parameters, such as steering and lane positioning, were also acquired. The results indicated that both circadian rhythms and driving duration had significant effects on self-reported fatigue levels and that the fatigue level increased faster in the evening group than the morning and noon groups. The results of the circadian rhythm analysis showed that a driver was most likely to feel tired between 14:00 and 16:00 and between 02:00 and 04:00, when the ability to stay within designated lane lines (lane maintenance) was significantly impaired for drivers in all three groups. The evening group drivers were the most at risk. The steering performance did not show a significant relationship with the self-reported fatigue level. The self-reported fatigue level is the result of the interactive effect of circadian rhythms and driving duration. The standard deviation of lane position was more correlated with circadian rhythms than with the steering reversal rate.

METANET model improvement for traffic control

The METANET model, deduced based on equilibrium state assumption, provides a candidate model for freeway traffic control design since it has both speed and density dynamics, but the previous work parameterized the speed control variable to be highly nonlinear, which caused difficulty in control design and implementation. Besides, the model could not catch quick and significant changes in traffic dynamics. This paper suggests improvement on the dynamics model in two aspects: (a) to drop the nonlinear parameterization in the speed control variable for simplicity; and (b) to propose several alternatives for the convection term of the speed dynamics. Model calibration using Berkeley Highway Lab data and simulation for comparison are presented to show the effectiveness of the improvements.

Comparison of Macroscopic and Microscopic Simulation Models in Modern Roundabout Analysis

Modern roundabouts are more and more widely used at both urban and rural intersections in North America. The results of traffic operations analysis at roundabouts often depend on the software used and parameters adopted. For an evaluation of types of traffic analysis tools on roundabout operations, a macroscopic traffic analysis software (SIDRA) and a microscopic simulation package (VISSIM) were used to analyze a two-lane roundabout at the intersection of two rural arterial highways in Alberta, Canada. A full range of traffic flow rates and left-turn proportions was loaded to the roundabout to compare the two traffic analysis tools and to evaluate the effects of different factors on the roundabout performance. Average control delay and 95% queue length were used as measures of effectiveness. Factors such as total traffic flow rate and left-turn vehicle proportion in each approach were analyzed to evaluate the sensitivity of the roundabout performance at different factor levels. The results showed that there was no significant difference for the delays predicted by VISSIM simulation and SIDRA at medium-to-high traffic flow rates and at all left-turn proportion levels. The 95% queue length predicted by VISSIM was longer than those predicted by SIDRA. Good correlation existed between predicted delays and 95% queue length from the two types of software. Both types of software needed parameter calibration for local traffic conditions. Roundabout capacity could also be estimated from a delay curve obtained from the method presented in this study.