Hongyun Chen

Landscaping of highway medians and roadway safety at unsignalized intersections

Well-planted and maintained landscaping can help reduce driving stress, provide better visual quality, and decrease over speeding, thus improving roadway safety. Florida Department of Transportation (FDOT) Standard Index (SI-546) is one of the more demanding standards in the U.S. for landscaping design criteria at highway medians near intersections. The purposes of this study were to (1) empirically evaluate the safety results of SI-546 at unsignalized intersections and (2) quantify the impacts of geometrics, traffic, and landscaping design features on total crashes and injury plus fatal crashes. The studied unsignalized intersections were divided into (1) those without median trees near intersections, (2) those with median trees near intersections that were compliant with SI-546, and (3) those with median trees near intersections that were non-compliant with SI-546. A total of 72 intersections were selected, for which five-year crash data from 2006-2010 were collected. The sites that were compliant with SI-546 showed the best safety performance in terms of the lowest crash counts and crash rates. Four crash predictive models-two for total crashes and two for injury crashes-were developed. The results indicated that improperly planted and maintained median trees near highway intersections can increase the total number of crashes and injury plus fatal crashes at a 90% confidence level; no significant difference could be found in crash rates between sites that were compliant with SI-546 and sites without trees. All other conditions remaining the same, an intersection with trees that was not compliant with SI-546 had 63% more crashes and almost doubled injury plus fatal crashes than those at intersections without trees. The study indicates that appropriate landscaping in highway medians near intersections can be an engineering technology that not only improves roadway environmental quality but also maintains intersection safety.

Development of Resource Allocation Strategies for Operating and Maintaining Traffic Signal Systems

Functional vehicle detection and signal system communication are essential for a traffic signal system to execute its intended coordinated signal timing plans. The degradations of vehicle detection and signal system communication could impose barriers to successful operations of a traffic signal system. To achieve and maintain an acceptable operational level set by a traffic agency, an agency has to prioritize its resource allocation. This paper first introduces the concept of traffic signal system performance. It defines a traffic signal system degradation index which measures the proportion of increased travel time attributable to failures in detection and communication components with respect to the total observed travel time of a traffic signal control section. The paper uses the degradation index and traffic simulation to evaluate the effectiveness of major strategies to improve vehicle detection and signal system communication. These strategies include upgrading detection technologies, improving the responsiveness to detection and communication repair work, providing adequate training, increasing the frequency of inspection, and installing a global positioning system (GPS) clock to maintain synchronization of the time clock in the controller. Finally, recommendations for optimal allocation of operation and maintenance resource allocation strategies for traffic signal systems are provided.

Cost Benefit Analysis of Freeway Service Patrol Programs: A Case Study in Florida

Floridas Road Rangers provide free highway assistance services during incidents on Floridas roadways to reduce delay and improve safety for the motoring public and responders. This paper presents the research results from a recently completed study to describe and quantify the benefits derived from the Road Ranger program. The Freeway Service Patrol Evaluation (FSPE) model, developed by the University of California at Berkeley, was used to quantify the benefit-cost (B/C) ratio using a variety of data from the Florida SunGuide database for the year 2010. The benefits (delay and fuel savings) of the Road Ranger program were about

The Timing to Retime and Maintain Traffic Signal Systems

135.3 million in total, and the costs (contract) were about

Impacts of Exit Ramp Type on the Safety Performance of Freeway Diverge Areas

19.9 million. Overall, the program achieved a B/C ratio of 6.78 in 2010. This paper will be informative for any agency looking to identify opportunities to improve the allocation of available funding for similar incident response programs.

Freeway deceleration lane lengths effects on traffic safety and operation

Currently, most agencies in the United States retime their traffic signal systems either every 2-4 years or based on complaints received. With limited budget and resources, it becomes essential for agencies to retime and maintain their traffic signal systems cost-effectively to maximize the benefits. To achieve this goal, this paper reviewed traffic signal retiming practices, and investigated the impact of signal timing degradation on traffic signal system performance. The impacts of signal timing degradations on the system performance for various growth rates were intensively simulated at three selected corridors. It was found that the elements of average traffic volume per hour per lane and the growth rate of traffic volume on a main corridor can be used to effectively estimate the signal timing degradation. This paper offers a simple and practical guideline to determine when to retime and maintain a traffic signal system.