William E Frawley

Estimating the Safety and Operational Impact of Raised Medians and Driveway Density: Experiences from Texas and Oklahoma Case Studies

This paper describes research sponsored by the Texas Department of Transportation to investigate the operational and safety impact of raised medians and driveway consolidation. Operational effects (travel time, speed, and delay) were investigated through microsimulation on three field test corridors and three theoretical corridors. Safety effects were investigated along 11 test corridors to estimate relationships between crash rates and access point densities as well as the presence of raised medians or two-way left-turn lanes (TWLTLs). The research demonstrates that access management effects are case specific and that microsimulation can assess these unique operational effects. For the case studies investigated, replacing a TWLTL with a raised median resulted in an increase in travel time on two test corridors and a decrease on one test corridor. Small increases in travel time were found with the theoretical corridors as well. The travel time differences are based on the traffic level and location and number of the raised median openings. When present, the relatively small increases in travel time, and subsequent speed and delay, appear to be outweighed by the reduction in the number of conflict points and increased safety. Detailed crash analysis on 11 test corridors indicated that as access point density increases, crash rates increase. This trend holds regardless of the median type. For test corridors in which crash data were investigated before and after the raised median installation, a reduction in the crash rate was always found. Finally, future research needs are identified, including the need to investigate operational and safety impact over a broader range of geometric conditions and longer corridors than investigated here.

Implementing a Program for Access Management in Texas: Lessons Learned

The Texas Department of Transportation recently sponsored research through the Texas Transportation Institute to provide recommendations for implementing a comprehensive access management program in the state. The research includes a provision to produce an access management guidebook for Texas for planners and engineers to use when planning, designing, and reviewing highway projects and access requests. This study describes some lessons learned in the research related to access classification, access spacing criteria, median alternatives, and overall implementation of the program. In terms of access classification, considerations include what type of access classification system is necessary to develop a successful program. For access spacing alternatives, lessons learned were related to what unsignalized access (driveway) spacing criteria guidelines are most applicable for adoption in Texas and why. In terms of lessons learned in overall implementation of the program, several questions were raised that have led to localized changes to the program that strengthened it overall. This study presents the results of these and other lessons learned, describes the background of access management, and outlines selected alternatives used in existing access management programs in other states. The status of the comprehensive access management program in Texas is presented. The research and experiences that emerged as a result of this project are expected to be useful to engineers and planners in Texas as well as other states that are developing or modifying comprehensive access management programs.

Evaluating the Michigan Access Management Program: Findings and Lessons Learned

As state departments of transportation (DOTs) and local transportation agencies make difficult funding decisions in these financially constrained times, access management improvements provide a cost-effective alternative for improving the safety and operation of roadways. Mindful of the benefits of implementing access management treatments, the Michigan DOT has conducted an access management program since 2002. The Michigan DOT contracted with the Texas Transportation Institute (TTI) to provide recommendations for adjustments to the Michigan access management program. As a result of the evaluation, TTI identified lessons learned related to the importance of (a) continuing support and funding for the access management program, (b) a clear access management policy statement, (c) coordination and cooperation between state and local transportation agencies, (d) continued training, (e) interagency coordination across state DOT divisions, (f) continued review and update of technical documentation and guidance, and (g) continued objective program evaluations. The lessons learned that are documented and described in this paper are invaluable reminders to practitioners in state DOTs with established programs and excellent points to consider for practitioners in state DOTs just beginning to foster access management implementation. Practitioners from local transportation agencies (e.g., cities, villages, counties, and townships) that are implementing access management or planning to implement access management will also find these lessons learned invaluable. The research community will also benefit from the lessons learned identified in this paper because the findings validate the procedural, political, and institutional considerations often touted as imperative to successful implementation of access management.