Jianhe Du

Design and Evaluation of Network Control Strategies Using the Macroscopic Fundamental Diagram

The Macroscopic Fundamental Diagram (MFD) has been demonstrated to exist on traffic networks. Researchers have proposed using MFDs to monitor the status of a traffic network to inform the design of network-wide traffic control strategies. Since the data needed to construct an MFD is not always readily available, estimating MFDs using a limited number of probe vehicle trajectory data with varied penetration rates is proposed. Subsequently, congestion control strategies are applied to the network and the MFDs are plotted for each control strategy. The results demonstrate that it is feasible to use the MFD estimated using limited probe data as an effective tool to monitor and control a network. The most effective strategy is a network-wide adaptive traffic signal control system, which decreases delays by up to 40%. Average fuel consumption levels decrease by up to 10%. Furthermore, combining control strategies without fully integrating them produces system-wide dis-benefits relative to running each system independently.

Evaluation of Impact of Modern Headlamp Technology on Design Criteria for Sag Vertical Curves

This paper includes a review of the current methodologies used in the design of sag vertical curves, a review of the changes in headlamp technologies, the results of a survey of practitioners and two visibility experiments, and conclusions. The review of the headlamp technology shows that, over time, headlamp technologies have increasingly limited the amount of light emitted above the horizontal axis of the headlamp. In addition to the regulatory impact, headlamp technologies such as visually optically aligned systems also limit the upward divergence of the light beam from the longitudinal axis of the vehicle (uplight). The practitioner survey found that very few deviations from AASHTO design methodologies were used. On the basis of the practitioner review, the potential to modify current methodologies is limited to the manipulation of the vehicle speed, deceleration, and change in angle of curvature. The results of the visibility experiments showed that participants detected objects at distances that were significantly shorter than the stopping sight distance (SSD), not only in sag vertical curves but also on flat roadway. This finding indicated that even if sag vertical curves were redesigned, visibility distance would still be shorter than SSD because the headlamps would be the limiting factor. A review of the potential modifications to the design of sag vertical curves (which were suggested in the responses to the practitioner survey) found that these changes would be inadequate to make up the difference between visibility distance and SSD.

Can Electricity Powered Vehicles Serve Traveler Needs

Electric vehicles (EV), Hybrid Electric Vehicles (HEV) or Plug-in Hybrid Electric Vehicles (PHEV) are believed to be a promising substitute for current gas-propelled vehicles. Previous research studied the attributes of different types of EVs and confirmed their advantages. The feasibility of EVs has also been explored using simulation, retrospective survey data, or a limited size of field travel data. In this study, naturalistic driving data collected from more than 100 drivers during one year are used to explore naturalistic driver travel patterns. Typical travel distance and time and qualified dwell times (i.e., the typical required EV battery recharging time between travels as based on most literature findings) are investigated in this study. The viability of electric cars is discussed from a pragmatic perspective. The results of this research show that 90 percent of single trips are less than 25 miles; approximately 70 percent of the average annual daily travel is less than 60 miles. On average there are 3.62 trips made between four-hour dwell times as aggregated to 60 minutes and 50 miles of travel. Therefore, majority of trips are within the travel range provided by most of the currently available EVs. A well-organized schedule of recharging will be capable of covering even more daily travels.

Approaches to Adaptive Lighting on Roadways

Adaptive lighting is an approach to lighting design that proposes to change the light level on a roadway on the basis of the needs of drivers. A review of the literature and building the connection between crashes and light level allowed the development of a system to select roadway luminance levels and then modify these levels on the basis of the needs of the driver. This adaptive lighting system uses parameters such as traffic volume, ambient light levels, pavement marking quality, intersection density, and, most important, the presence of pedestrians to allow lighting design criteria to be selected through a weighting system. As these parameters (such as traffic volume) change, a new light requirement is determined, and the lighting system can be adjusted with controllable luminaires and a master control system. Guidelines for the implementation of this system and an example are provided.

Feasibility of Using In-Vehicle Video Data to Explore How to Modify Driver Behavior That Causes Nonrecurring Congestion

This research report—a product of the Reliability focus area of the second Strategic Highway Research Program (SHRP 2)—presents findings on the feasibility of using existing in-vehicle data sets, collected in naturalistic driving settings, to make inferences about the relationship between observed driver behavior and nonrecurring congestion. General guidance is provided on the protocols and procedures for conducting video data reduction analysis. In addition, the report includes technical guidance on the features, technologies, and complementary data sets that researchers should consider when designing future instrumented in-vehicle data collection studies. Finally, a new modeling approach is advanced for travel time reliability performance measurement across a variety of traffic congestion conditions.

Large-scale Agent-based Multi-modal Modeling of Transportation Networks - System Model and Preliminary Results.

The performance of urban transportation systems can be improved if travelers make better-informed decisions using advanced modeling techniques. However, modeling city-level transportation systems is challenging not only because of the network scale but also because they encompass multiple transportation modes. This paper introduces a novel simulation framework that efficiently supports large-scale agent-based multi-modal transportation system modeling. The proposed framework utilizes both microscopic and mesoscopic modeling techniques to take advantage of the strengths of each modeling approach. In order to increase the model scalability, decrease the complexity and achieve a reasonable simulation speed, the proposed framework utilizes parallel simulation through two partitioning techniques: spatial partitioning by separating the network geographically and vertical partitioning by separating the network by transportation mode for modes that interact minimally. The proposed framework creates multi-modal plans for each trip and tracks the travelers trips on a second-by-second basis across the different modes. We instantiate this framework in a system model of Los Angeles (LA) supporting our study of the impact on transportation decisions over a 5 hour period of the morning commute (7am-12pm). The results show that by modifying travel choices of only 10% of the trips a significant reduction in traffic congestion is achievable that results in better traffic flow and lower travel times.

Sag Vertical Curve Design Criteria for Headlight Sight Distance

This document is the final report for NCHRP Project 15-41, “Sag Vertical Curve Design Criteria for Headlight Sight Distance.” This report includes a review of the current methodologies used in the design of sag vertical curves, a review of the changes in headlamp technologies, the results of the survey of practitioners, two visibility experiments, and discussion on potential changes to the American Association of State Highway and Transportation Officials (AASHTO) design guide. The review of the headlamp technology shows that, over time, headlamp technologies have had increasing limitation on the amount of light emitted above the horizontal axis of the headlamp. In addition to the regulatory impact, headlamp technologies such as visually optically aligned technologies also limit uplight. In the practitioner survey, it was found that very few deviations from the AASHTO design methodologies were used. Based on the practitioner review, the potential to modify the current methodologies is limited to the manipulation of the vehicle speed, deceleration, and the angle of curvature change. The results of the visibility experiments found that participants detected objects at distances which were significantly shorter than the safe stopping distance (SSD). This occurred not only in sag vertical curves, but also on flat roadway. This indicated that even if sag vertical curves were redesigned, visibility distance would still be shorter than SSD because the headlamps would be the limiting factor. A review of the potential modifications to sag vertical curve designs (which were suggested as a result of the practitioner survey) found that these changes would be inadequate to make up the difference between visibility distance and SSD.