Authors: Dr. Jie Yu, Dr. H. W. Ho, & Dr. Gang-Len Chang
Date: April 2010
Abstract:
This study offers a comprehensive review of the safety improvement programs adopted by Maryland, FHWA (SafetyAnalyst), and other state agencies, focusing mainly on the following imperative issues: (1) screening and ranking high-crash locations, (2) prioritizing cost-effective projects for safety improvement; and (3) conducting before/after studies for project implementation plans. Based on the resultsof this review, we recommend that the following enhancements be incorporated into the existing safety improvement program in Maryland: (1) develop a multi-criteria method to enhance the current procedures used by the Maryland SHA to select and rank high-crash locations; (2) using SPFs and the observed crash frequency to reliably estimate the site-specific crash frequency: (3) developing and calibrating SPFs for Maryland:; (4) using negative binomial distribution to represent the variation of crash frequency; (5) developing and calibrating the crash reduction functions with local data; (6) including secondary costs/benefits in the evaluation; (7) using SPFs of the after period in estimating the do-nothing crash frequency; and (8) Employing nonlinear models for estimating future traffic volume.

Download (MD-10-SP808B4C-Crash-Analysis-and-Prediction-Phase-I-Report.pdf)

Authors: Gang-Len Chang & Sung Yoon Park
Date: Dec. 2010
Abstract:
This report presents the research results of two ITS applications: The first is an innovative field implementation of variable speed limit (VSL) control for a recurrently congested highway segment, and the second is a laboratory experiment of a lane-based signal merge (LBSM) control for highway work zone. VSL control is an advanced traffic management strategy (ATMS) that has received increasing interest from the transportation community since the advent of intelligent transportation systems (ITS) in the 1980s. A complete VSL system typically comprises a set of traffic sensors to collect flow and speed data, several properly located variable message signs (VMSs) to display messages, a reliable control algorithm to compute the optimal speed limit for all control locations, a real-time database, and a communications system to convey information between all principal modules. The field experimental results over a 10-week period clearly indicate that VSL control supplemented with the display of estimated travel times can significantly increase both the average speed and throughput for highway segments plagued by recurrent congestion. LBSM is a new merge control strategy that employs a signal at the proper merging point to assign the right-of-way for traffic in each lane if the approaching volume exceeds 800 vehicles per hour per lane. The results of extensive simulation evaluation clearly indicate that the design, even preliminary in nature, can significantly increase the throughput and reduce the average vehicle delay, average vehicle stop delay, and the number of vehicle stops for highway work zones under congested traffic conditions.

Download (MD-10-SP608B4J_Applying-ITS-Technologies-to-Contend-with-Highway-Congestion_VSL-LBS_Report.pdf)

Authors: Gang- Len Chang & Nan Zou
Date: May. 1, 2009
Abstract:
This study aims to assist the Maryland State Highway Administration (SHA) in evaluating the performance of License Plate Recognition (LPR) technology and its reliability to support the travel time estimation applications on local arterials. The evaluation results will help SHA determine the effectiveness of using the LPR technology for improving work-zone operations. In this study, the research team at the University of Maryland designed a LPR-based real-time travel time estimation system and deployed the system at four different sites on southbound MD201 (Kenilworth Ave.). The evaluation results show that the LPR unit is able to capture about 65.9% of the passing traffic and correctly recognize about 72.5% of those captured plate images. The travel time estimation system was able to match license plates from 36.3% of the through traffic when most traffic volumes passed both LPR sites in the demonstration Period-1. The availability of matched license plates dropped significantly when there exists one or more major intersection and ramps between the two LPR sites.

Download (MD-09-SP708B4G_License-Plate-Recognition-Technology-Evaluation-Report.pdf)

Date: April. 21, 2009

Download (MD-09-SP708B4C_Integrated-Knowledge-Based-System-for-Real-Time-Estimation-of-Incident-Durations_Summary.pdf)

Authors:  DR. GANG-LEN CHANG & DR. NAN ZOU
Date: Dec. 29, 2009
Abstract:
This project produced an integrated computer system that enables engineers at the Maryland State Highway Administration to analyze the impact of a work-zone operational plan and to estimate the resulting cost/benefit. The proposed system consists of an intelligent user-interface, an analytical computing module, a microscopic simulation model, and an output analysis module. Depending on the nature of a proposed work-zone plan, one can either perform the preliminary estimate with the embedded analytical module or conduct an in-depth cost-benefit analysis with its simulation model. To capture the unique behavioral patterns of local drivers in response to perceived work-zone operations, this study conducted a series of field observations on car-following, lane-changing, and headway distributions among vehicles approaching lane-closure locations, and applied all field-observed information in calibrating key model parameters. This is to ensure that all analysis results produced from the proposed work-zone analysis program accurately reflect the actual benefits, costs, and resulting traffic impacts on Maryland’s highway.

Download (MD-09-SP708B4B_LCAP-Report.pdf)

Authors: Gang-Len Chang & K.P. Kang
Date: July 2008
Abstract:
To improve traffic mobility and safety in highway work zones, this study has focused mainly on developing advanced merge and speed control strategies, including both their individual and integrated control algorithms. Based on the deficiencies and limitations of existing work zone control operations, this research has made contributions mainly on the following four regards:(1) understanding traffic flow characteristics under work zone traffic conditions with empirical data and identifying their interrelations; (2) developing an operational model for computing the optimal set of thresholds for DLM and its implementation algorithm; (3) Proposing an optimal speed limit control model that can maximize the throughput of a lane-closure highway segment with a set of dynamically adjusted speed limits; and (4) constructing an integrated operational algorithm to take the advantage of the strengths of DLM and VSL controls. The simulation results have demonstrated that the developed DLM and VSL controls have better performance in terms of traffic mobility and safety than their existing controls based on static approaches, and also shown that the proposed integrated control of the DLM and VSL control has more promising properties than each individual control.

Download (MD-08-SP508B4F_VSL-DLM_Report.pdf)

Authors: Gang-Len Chang & Kyeong-Pyo Kang
Date: Aug. 1, 2005
Abstract:
This project presents the evaluation results of three ITS technologies offered by system providers for improving operational efficiency and traffic safety at highway work zones. The first is an integration of variable message signs (VMS) and sensors that function to guide traffic approaching the work zone via dynamic late merge (DLM) operations. Observations of the day-to-day traffic patterns over the work zone under DLM control clearly indicate that such a control system has the potential to significantly increase the work zone throughput, reduce the queue length, and vehicle delay if all sensors and VMS are placed at proper locations.
The second technology is a travel time prediction system that employs traffic data from sensors to project the travel time from a set of given origins to the target destination. The field test results from the highway segment along EB I-70 from MD 32 to I-695 reveal that prediction of travel times under moderate and stable traffic conditions is likely to yield an acceptable level of reliability. However, much remains to be improved for achieving reliable prediction of travel times under congested and unstable traffic flows.
The third target technology under evaluation is a license plate recognition (LPR) system that computes the travel time between an O-D pair based on the entry and exit times of a matched license plate number. The performance of the LPR system on the I-95 testing site shows that the employed technology for LPR cannot yield a sufficient level of license recognition rate for reliable estimation of travel times unless the target highway segment is under congested traffic conditions and vehicles are moving under relatively slow speeds. Besides, the LPRS may not be a cost-effective system for use in local arterials with a large percentage of turning flows, which often causes the LPRS to have a low match rate.

Download (MD-05-SP208B4H-Evaluation-of-ITS-Deployments-for-Work-Zone-Operations-Report.pdf)

Authors: Gang-Len Chang, Hua Xiang & Chi-Sheng Chou
Date: June 2004
Abstract:
This study has investigated the interrelations between crash rates, signal yellow times, driver characteristics and vehicle performance characteristics at signalized intersections, based on field observations of 732 drivers at nine intersections across five counties in Maryland. It has been found that driver responses during the yellow signal phase can be classified into four distinct types: “aggressive pass,” “conservative stop,” “normal stop,” and “normal pass.” Their response differences are due not only to discrepancies in individual characteristics, but also a variety of traffic environmental factors. The collective impacts of such factors have been evaluated with an ordered-probit model. In addition, based on the speed evolution data recorded from each observed driver, this study further analyzed the deceleration/ acceleration rates of drivers responding to yellow-light phases. Such information provides valuable data for computing the distribution of intersection dilemma zones under various types of driving populations and vehicle types.

Download (MD-04-SP308B4L-Dilemma-Zone-Warning-System-Phase-I-Report.pdf)

Download (Jinshan_report_1.pdf)

Download (HWHo_Report_4.pdf)