No abstract

In some states (e.g., Texas), frontage roads have been a design solution for providing access along rural freeways and access-controlled principal arterials. In rural and lesser-developed urban areas, the frontage roads are usually operated as two-way facilities because of relatively long distances between interchanges. As areas become more urban and the adjacent land is developed, traffic volumes increase, and as interchange spacing decreases, it becomes desirable to convert the frontage roads to one-way operation. There is a need to objectify safety impacts of frontage road conversion, and business and property owners are often concerned with economic impacts related to access, business activity, and property values. Recognizing these needs and concerns, the Texas Department of Transportation contracted with the Texas A&M Transportation Institute to investigate the safety and economic impacts of converting two-way frontage roads to one way. Researchers investigated eight sites throughout Texas: both conversion sites and comparison sites that remained two way. Researchers developed 12 crash modification factors by crash severity and crash type for frontage road conversion. A sample application is provided in this paper. To assess economic impacts, researchers obtained parcel-level appraisal data and found overall increases in appraised values. Researchers surveyed business owners and managers and customers. Researchers found that business owners and managers are typically concerned with access, gross sales, and ramp and interchange locations and spacing. Finally, researchers identified lessons learned with the crash data for those performing safety analyses.

The Texas Department of Transportation has identified the need for a more accurate estimation of vehicle miles traveled (VMT) on streets functionally classified as local. The Texas Transportation Institute developed a procedure to select traffic count sites randomly on local streets that results in a statistically valid estimation of local street VMT. The primary goal was to yield a statistically valid median traffic volume to apply to road segments on which no count is taken. This procedure involves grids overlaid on maps depicting the functional classifications of streets in a given area. All grid cells are assigned sequential numbers, and then a relative range of random numbers is generated. The actor then locates the grid cells that correspond to the randomly selected numbers in the order in which they were generated. Each time a cell that contains a local street is selected, the actor highlights it and marks a count location on the map. This process is repeated until an appropriate number of sites have been selected. Statistical analyses have determined how many count locations are necessary to provide a representative sample of traffic counts in each area, depending on the population. By an oversampling in a variety of areas, median values of observed volumes identify the number of counts at which the diminishing rate of return on the investment in the counts occurs. This procedure has resulted in median traffic count volumes on local streets that more realistically represent the variety of local streets that exist. These median volumes derived from randomly selected sites are considerably lower than the median volumes derived from historical count locations that are not randomly selected. In addition, there are now randomly selected traffic count locations in area types of some counties in which no counts were previously performed. FHWA has approved this random traffic count site selection process for use and has acknowledged it as a “most noteworthy state activity” related to estimating local street VMT ( www.fhwa.dot.gov/ohim/statepractices.pdf ).

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.

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.