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Connelly Springs, MD, United States

Zhu S.,George Mason University | Kim W.,University of Maryland University College | Chang G.-L.,University of Maryland University College | Rochon S.,Office of Traffic and Safety
Journal of Transportation Engineering | Year: 2014

Both patrolling and prepositioned strategies for allocating emergency traffic response units have been implemented in practice. To compare the performance of both response strategies, this study has conducted an efficiency comparison based on the field data from the I-495/I-95 Capital Beltway. The extensive experimental results have revealed that the effectiveness of those response strategies varies with some critical factors, including the spatial distribution of incident frequency over different times of a day, the fleet size of the response team, the congestion level, and the available detection sources. In view of the resource constraints, the study has further presented a methodology to determine the most cost-beneficial fleet size operated with the proposed strategies, considering the marginal cost and the benefit of an additional response unit on the resulting total social benefits. The analysis results with the data from the Capital Beltway could serve as the basis for highway agencies to review and optimize their incident response and management program. © 2014 American Society of Civil Engineers. Source


Yang X.,University of Maryland University College | Chang G.-L.,University of Maryland University College | Rahwanji S.,Office of Traffic and Safety
Journal of Transportation Engineering | Year: 2014

As one of the most popular unconventional interchange designs, diverging diamond intersection (DDI) has received increased attention over the past decade. Through a reverse operation of traffic movements between its two crossover intersections, DDI can accommodate more traffic movements within each phase. To design an effective signal plan for DDIs, one needs to address the following two critical issues: (1) how to select the common cycle length and green splits at each crossover intersection under different geometric conditions, and (2) how to coordinate a DDI's two crossover intersections with its adjacent conventional intersections. To contend with these issues, this paper presents an optimization model with the objective of maximizing intersection capacity to yield the optimal green splits and cycle length. Also, in view of the potentially large left-turn traffic volumes from the freeway off-ramps, this study has further modified a model to provide progressions to both left-turn and through traffic paths. Using simulation software as an unbiased tool, this study has conducted extensive simulation comparisons between the optimized signal plans and the results from signal optimization software under various traffic scenarios. The experimental results confirm the promising properties of the proposed signal models for DDI, especially if the traffic progression between two crossover intersections is the major concern. © 2014 American Society of Civil Engineers. Source


Peek-Asa C.,University of Iowa | Peek-Asa C.,Injury Prevention Research Center | Britton C.,University of Iowa | Britton C.,Injury Prevention Research Center | And 3 more authors.
Journal of Safety Research | Year: 2010

Background: Previous research has identified teenage drivers as having an increased risk for motor-vehicle crash injury compared with older drivers, and rural roads as having increased crash severity compared with urban roads. Few studies have examined incidence and characteristics of teen driver-involved crashes on rural and urban roads. Methods: All crashes involving a driver aged 10 through 18 were identified from the Iowa Department of Transportation crash data from 2002 through 2008. Rates of overall crashes and fatal or severe injury crashes were calculated for urban, suburban, rural, and remote rural areas. The distribution of driver and crash characteristics were compared between rural and urban crashes. Logistic regression was used to identify driver and crash characteristics associated with increased odds of fatal or severe injury among urban and rural crashes. Results: For younger teen drivers (age 10 through 15), overall crash rates were higher for more rural areas, although for older teen drivers (age 16 through 18) the overall crash rates were lower for rural areas. Rural teen crashes were nearly five times more likely to lead to a fatal or severe injury crash than urban teen crashes. Rural crashes were more likely to involve single vehicles, be late at night, involve a failure to yield the right-of-way and crossing the center divider. Conclusions: Intervention programs to increase safe teen driving in rural areas need to address specific risk factors associated with rural roadways. Impact on Industry: Teen crashes cause lost work time for teen workers as well as their parents. Industries such as safety, health care, and insurance have a vested interest in enhanced vehicle safety, and these efforts should address risks and injury differentials in urban and rural roadways. © 2010 National Safety Council and Elsevier Ltd. Source


Hochstein J.L.,Iowa State University | Maze T.H.,Iowa State University | Souleyrette R.R.,Iowa State University | Stout T.B.,Iowa State University | And 3 more authors.
Transportation Research Record | Year: 2010

A rural expressway is a high-speed, multilane, divided highway with partial access control with both at-grade intersections and grade-separated interchanges. Many state transportation agencies are converting rural two-lane undivided highways into expressways for improved safety and mobility. However, collisions at two-way stop-controlled (TWSC) expressway intersections are reducing the safety benefits that should be achieved after conversion. When the safety performance of these intersections deteriorates, the countermeasure path typically begins with several signing, marking, or lighting improvements, followed by signalization, and could ultimately result in grade separation. Signals are not always effective at improving safety and hamper the mobility expressways are meant to provide. Interchanges are not economically feasible at every problematic intersection and can take years to develop; therefore, more design options at TWSC rural expressway intersections are needed. Some state transportation agencies have experienced success with innovative rural expressway intersection countermeasures that are not currently included as design options within national guides. Therefore, NCHRP Report 650: Median Intersection Design for Rural High-Speed Divided Highways, was commissioned to recommend revisions to AASHTO's A Policy on Geometric Design of Highways and Streets (Green Book) and the Manual on Uniform Traffic Control Devices (MUTCD) regarding rural expressway intersection design. Project tasks included summarizing existing expressway intersection design guidance within these national guides, documenting state transportation agency experience with innovative rural expressway intersection safety treatments, and recommending revisions to the Green Book and the MUTCD. Source


Yang X.,University of Maryland University College | Chang G.-L.,University of Maryland University College | Rahwanji S.,Office of Traffic and Safety | Lu Y.,University of Maryland University College
Journal of Transportation Engineering | Year: 2013

Despite the increasing use of continuous-flow intersections (CFIs) to contend with the congestion caused by heavy through and left-turn traffic flows, a reliable and convenient tool for the traffic community to identify potential deficiencies of a CFI's design is not yet available. This is due to the unique geometric feature of CFI, which comprises one primary intersection and several crossover intersections. The interdependent relationship between traffic delays and queues at a CFI with five closely spaced intersections cannot be fully captured with the existing analysis models, which were developed primarily for conventional intersections. In response to such a need, this study presents a comprehensive analysis for the overall CFI delay, identifies the potential queue spillback locations, and develops a set of planningstage models for the CFI design geometry. To facilitate the application of these proposed models, this paper also includes a case study of a CFI at the intersection of MD 4 and MD 235 constructed by the Maryland State Highway Administration. © 2013 American Society of Civil Engineers. Source

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