Robert S Foyle

Operational and safety effects of U-turns at signalized intersections

In an effort to balance vehicular safety, mobility, and access, many transportation officials favor the use of raised median cross sections on highways. However, this decision leads to much controversy from those opposed to the resulting lack of direct driveway access. One of the issues in this controversy is the effect of increased U-turns at adjacent intersections. The purpose of this research was to determine the operational and safety effects of U-turns at signalized intersections. The operational analysis involved measurements of vehicle headways in exclusive left-turn lanes at 14 signalized intersections. Regression analysis of saturation flow data showed a 1.8% saturation flow rate loss in the left-turn lane for every 10% increase in U-turn percentage and an additional 1.5% loss for every 10% U-turns if the U-turning movement was opposed by protected right-turn overlap from the cross street. The safety analysis involved a set of 78 intersections. Fifty-four sites were chosen randomly, and 24 sites were selected on the basis of their reputation as U-turn problem sites. Although the group of study sites was biased toward sites with high U-turn percentages, the study found that 65 of the 78 sites did not have any collisions involving U-turns in the 3-year study period. U-turn collisions at the remaining 13 sites ranged from 0.33 to 3.0 collisions per year. Sites with double left-turn lanes, protected right-turn overlap, or high left-turn and conflicting right-turn traffic volumes were found to have a significantly greater number of U-turn collisions.

Operational Effects of Signalized Superstreets in North Carolina

Arterials across the United States are operating inefficiently and are becoming increasingly congested because of growing traffic demand. Agencies tasked with improving these arterials are running out of good solutions. Superstreets, called restricted crossing U-turns by FHWA, are part of a menu of unconventional arterial designs that may provide promising solutions. Up to this point, little valid information exists on the operational effects of superstreets because study results have been from macroscopic analyses and simulations of hypothetical arterials. The purpose of this research was to determine the operational effects of the superstreet treatment on existing signalized arterials in North Carolina. The operational analysis involved calibrating and validating VISSIM models of three existing signalized superstreets in North Carolina; two isolated intersections and one five-intersection superstreet corridor. After some adjustments, the team produced VISSIM models that provided travel times within an acceptable range of the field data collected. Results from the three calibrated VISSIM models were compared with results from models of equivalent conventional sites at various volume levels with travel time as the primary measure of effectiveness. The superstreet outperformed the conventional design at each location studied and reduced the overall average travel time per vehicle traveling through the intersection. The travel time savings and extra capacity at higher volumes can buy agencies more years of acceptable operation before intersection improvements, or even interchanges, are necessary.

Safety effects of unsignalized superstreets in North Carolina

Arterials across the United States are experiencing far too many collisions. Agencies tasked with improving these arterials have few available effective solutions. Superstreets, called restricted crossing u-turns by the Federal Highway Administration (FHWA), are part of a menu of unconventional arterial intersection designs that may provide a promising solution. Up to this point, there is little valid information available on the safety effects of superstreets, as study results have been from basic analyses that only account for traffic volume changes. The purpose of this research was to determine the safety effects of the unsignalized superstreet countermeasure on existing arterials in North Carolina. The safety study involved traffic flow adjustment, comparison-group, and Empirical Bayes analyses of 13 unsignalized superstreet intersections in North Carolina. The superstreets have been installed in the last few years across the state as opportunities presented themselves, but not necessarily at the most hazardous sites. The unsignalized superstreet countermeasure showed a significant reduction in total, angle and right turn, and left turn collisions in all analyses. Analyses also showed a significant reduction in fatal and injury collisions. The authors recommend that future analysts use a crash modification factor of 46 percent when considering the conversion of a typical unsignalized arterial intersection into a superstreet.

Business Perceptions of Access Management Techniques

Transportation agencies have made significant strides to reduce collisions and increase capacity along strategic highway corridors. Efforts have led to the implementation of many different access management techniques along corridors, such as installing medians versus two-way left-turn lanes and closing median openings. Businesses along these corridors have indicated their concern that these new designs will have a negative economic impact on their business because of the lack of direct access to their properties. The objective of this study was to quantify the business perceptions of median treatments on businesses adjacent to multilane highways. Owners of businesses along treatment corridors viewed median installations with a more positive outlook following implementation of the median than they did prior to the installation. The performance of treatment sites in terms of reported impacts on business revenues indicates that there is no direct evidence of negative economic impacts due to median installations.

Resident, Commuter, and Business Perceptions of New Superstreets

AbstractSuperstreets are an unconventional at-grade intersection design that have significant potential to help with safety and delay. The purpose of this paper is to formally evaluate residential, commuter, and business owner opinions of superstreets across North Carolina through feedback from three separate surveys. Findings from each of the surveys provide interesting feedback. Residents living near superstreets agree the design helps them travel more safely through the intersection. Commuting drivers perceive superstreets to be more difficult to navigate, but feel strongly about savings in travel time and reductions in numbers of stopped vehicles. Business reactions varied greatly depending on the ability to make direct left turns from the arterial. In general, more business managers feel superstreets negatively impact business growth and operations. Based on the opinions of adjacent business owners/managers, access and confusion were identified as key problems in retaining the number of regular custo...