Christopher Cunningham

Development and Implementation of Conflict-Based Assessment of Pedestrian Safety to Evaluate Accessibility of Complex Intersections

This paper describes the development and implementation of the conflict-based assessment of pedestrian safety (CAPS) methodology for the evaluation of pedestrian accessibility at complex intersections. Significant research has explored pedestrian access to modern roundabouts and other complex intersections, and a significant focus has been placed on accessibility for pedestrians who were blind. A majority of these studies relied on actual street crossings by study participants under the supervision of a trained orientation and mobility specialist. These crossing studies quantified risk from a measurement of intervention events, in which the orientation and mobility specialist had to physically stop the participant from crossing. Although such studies provide useful data on the crossing risk at a particular intersection, street crossings can be dangerous to the study participants and are time-consuming and expensive to conduct. The CAPS method emphasizes the use of conflict-based safety factors to quantify risk in a framework compatible with indicator studies. This method relates pedestrian crossing decisions to advanced measurements of vehicle dynamics to estimate lane-by-lane conflicts and identifies the grade of conflict on the basis of a five-criterion rating scale. The CAPS framework was applied to a study of crossings by blind pedestrians at a multilane roundabout. The resulting risk scores were calibrated from the actual orientation and mobility interventions observed during the study. The calibrated CAPS framework correctly matched all (high-risk) orientation and mobility intervention events and further identified other (lower-risk) pedestrian–vehicle conflicts. The CAPS framework provides a more efficient, objective, and consistent safety assessment of pedestrian crossings in a research context, without the need for pedestrians to step into the roadway.

Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities

This report is intended to provide practitioners with useful information related to establishing safe crossings at roundabouts and channelized turn lanes for pedestrians with vision disabilities. The specific focus areas of the report provide guidance on: identifying under what conditions pedestrians with vision disabilities may experience problems with crossing performance; tying treatment solutions to specific crossing challenges faced by the visually impaired pedestrian population; conducting pedestrian/vehicle studies that help identify performance problems and appropriate treatment strategies; quantifying pedestrian accessibility at a particular crossing; presenting findings from selective field studies performed through this research; developing approaches for extending research findings to other locations; and discussing implications for the practitioner in terms of treatment selection and facility design. The results of this research will be useful to engineers, the accessibility community, policy makers, and the general public to aid in understanding the specific challenges experienced at these facilities by pedestrians with vision disabilities. It is only through the understanding of the components of the crossing task and the particular challenges involved that solutions can be developed, installed, and evaluated appropriately.

Simulator Study of Driver Responses to Pedestrian Treatments at Multilane Roundabouts

Previous studies have shown that roundabouts, especially multilane roundabouts, pose accessibility challenges to pedestrians with vision impairments, in part because of a lack of yielding by drivers, especially on multilane roundabout exit legs. In this study, a driving simulator was used to assess three different treatments in regard to their propensity for increasing the driver yielding rate. These treatments were the relocation of the stop bar and crosswalk away from the beginning of the exit leg and two types of beacons, namely a pedestrian hybrid beacon (PHB) and a rectangular rapid flashing beacon (RRFB). The study showed that the installation of any kind of beacon (PHB or RRFB), with or without crosswalk relocation, increased driver yielding rates significantly. Relocating the crosswalk did not provide a significant increase in the driver yielding rate for the base case, but appeared to enhance further the effectiveness of the PHB and RRFB treatments. The results of using an eye tracker on drivers to track their gaze pattern while exiting the roundabout showed that having a beacon installed with crosswalk relocation increased drivers’ attention on the beacon and on the pedestrian along the road. However, some of the participants failed to see and react to the pedestrian treatments and thus caused concern about the visibility of these treatments at the roundabout exit leg.

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.

Analysis of Automated Speed Enforcement Cameras in Charlotte, North Carolina

The effects of a mobile automated speed enforcement system in Charlotte, North Carolina, were examined. Limited focus groups were conducted to characterize resident and professional attitudes, opinions, and beliefs regarding such a speed program. Overall, opinions were positive. The system, consisting of three mobile units, was implemented along 14 corridors. Two separate analyses were conducted on data collected from January 2000 to December 2005. Findings from a previous study done for the North Carolina Governors Highway Safety Program were updated. The first, and primary, analysis was a before-and-after analysis of collisions. This study used Hauers comparison group methodology. Three different collision data sets were analyzed: total collisions, data accounting for regression to the mean, and data for five heavily enforced corridors. On the basis of the analysis, the impact of regression to the mean appears to be negligible. The results indicate that the camera program likely reduced collisions in corridors with automated enforcement. The second analysis observed whether compliance with posted speed limits was enhanced. Mean speeds, median speeds, 85th percentile speeds, and percentages of drivers more than 10 mph over the speed limit were analyzed. The analyses found speed reductions caused by the camera program. On the basis of these findings, it was recommend that the City of Charlotte continue the automated speed enforcement program. Other agencies considering speed camera programs can benefit from the knowledge gained in Charlotte.

Reasonable speed limits on suburban multilane highways with curbs

When some two-lane roads with 55 mph speed limits are widened to four through lanes, curb and gutter is installed to address issues such as access control, difficult terrain, and limited right-of-way. Posted speed limits along such highway segments are typically decreased to 45 mph in North Carolina because of guidance in the AASHTO Green Book and elsewhere that vertical curbs should not be placed next to high-speed lanes. Although much money is spent to improve such roadways, the results may be viewed negatively by the public, design professionals, and law enforcement personnel. Drivers may be unhappy about getting tickets or driving more slowly, designers are unhappy about being blamed by the public, and police are unhappy about the increased enforcement burden. To help resolve such a dilemma, in this research the team collected relevant data such as speeds and collisions on four-lane road sections with curbs that have 45 or 55 mph speed limits and nontraversable medians or two-way left-turn lanes. The team found that the speed limit does not seem to make an important difference in collision rates or severities for the roads the team examined. The higher speed limit also made relatively small differences in the mean speeds and speed variances observed. Considering all results, the researchers recommended that the North Carolina Department of Transportation continue its current policy of allowing 55 mph speed limits on four-lane roads with curbs on a selective, case-by-case basis.

Nonmotorized Site Selection Methods for Continuous and Short-Duration Volume Counting

This paper outlines the process for selecting sites to perform counts on transportation facilities in the context of establishing a nonmotorized traffic volume counting program. Many agencies are well practiced in collecting motor vehicle traffic counts and estimating annual average daily traffic volumes for motor vehicles on the basis of knowledge founded on years of research and experience. Selecting sites is one component of developing a consistent system for quantifying nonmotorized travel so bicycle and pedestrian volumes can ultimately feed into tools to measure existing trends and model future increases in nonmotorized trips at site, corridor, and regional levels. The outcome of collecting count data can ultimately assist in evaluating facility usage over time, better inform the project prioritization process, and provide evidence to support nonmotorized facility inclusion through Complete Streets planning and improve planning for active transportation. This paper outlines the goals of a nonmotorized traffic monitoring program and objectives of the site selection process. From the experience of a pilot project conducted by the North Carolina Department of Transportation, the site selection method details the following components: gathering potential sites, conducting a site visit, gathering additional data needed to inform the decision-making process, and ultimately selecting sites and developing an equipment inventory.

Considerations for Effective Lidar Deployment by Transportation Agencies

Lidar is becoming increasingly popular across the United States, and state transportation agencies are adopting this technology for practical uses in transportation-related applications. This trend can be seen in the growing number of agencies acquiring lidar scanners and contracting lidar services. The primary factors behind this trend are that (a) surveyors, engineers, and technicians are becoming more educated about and increasingly open to lidar and its applications and (b) lidar is potentially more cost-effective than traditional surveying technologies. Lidar can provide transportation agencies with the benefits of safety, data collection productivity, cost-effectiveness, applicability, high levels of detail, and technological advancement. Many of the more practical uses and benefits of lidar have come to fruition in recent years, and transportation agencies have been more open to its use. However, little more than anecdotal evidence supports when a specific lidar platform should be applied for various applications rather than a traditional surveying method. Decision makers in geomatic and surveying departments that use lidar must regularly weigh the options of which surveying method to use for specific projects and base decisions on performance tradeoffs. The methodology presented in this paper aims to provide guidance on how agencies may determine whether lidar can be practically used within their organizations. The aspects and performance measures outlined for effective deployment of lidar equipment or contracted services should be systematically considered.

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.

Safety Evaluation of Seven of the Earliest Diverging Diamond Interchanges Installed in the United States

Diverging diamond interchanges (DDIs) are increasingly popular because they provide improved traffic operations and cost savings. On the basis of theory, DDIs should be safer than conventional diamonds, but previous empirical safety studies have been limited. The objectives of this work were, therefore, to conduct a broader safety evaluation of DDIs and to recommend a crash modification factor (CMF) for the conversion of a conventional diamond to a DDI. The team analyzed seven of the earliest DDIs in the United States. Four were in Missouri and other sites were in Kentucky, New York, and Tennessee. The team collected more than 28 site years of crash and other data before intersection conversion and more than 19 site years of data after their conversion. The primary analysis was before and after with comparison sites to account for trends and potential simultaneous event biases. The results showed that crashes were reduced at most of the sites, and the team recommended a CMF of 0.67, meaning that installation of a DDI to replace a diamond should reduce all crashes by 33%. The reduction in injury crashes was even larger, with the team recommending a CMF of 0.59. Other analyses indicated that DDI installation should mean a substantial reduction of angle and turning crashes, with some reduction in rear-end crashes as well, although rear-end crashes will still be the dominant crash types after DDI installation. Clearly, DDIs offer potential safety benefits, and agencies should consider them strongly as replacements for conventional diamonds.