David L Harkey

Development of the bicycle compatibility index

Presently, there is no methodology that is widely accepted by engineers, planners, or bicycle coordinators that will allow them to determine how compatible a roadway is for allowing efficient operation of both bicycles and motor vehicles. Determining how existing traffic operations and geometric conditions affect a bicyclist’s decision to use or not use a specific roadway is the first step in determining the bicycle compatibility of the roadway. The Federal Highway Administration sponsored a study in which a methodology for deriving a bicycle compatibility index was developed. This tool can be used by bicycle coordinators, transportation planners, traffic engineers, and others to evaluate the capability of specific roadways to accommodate both motorists and bicyclists. It is intended to provide practitioners with the ability to assess the bicycle level of service present on existing facilities or on proposed facilities and can be used for operational, design, and planning analyses.

EVALUATION OF SHARED-USE FACILITIES FOR BICYCLES AND MOTOR VEHICLES

This study was conducted for the Florida Department of Transportation with an objective of evaluating the safety and utility of shared-use facilities to provide engineers and planners comprehensive results that can be used in planning, designing, and constructing roadways to be shared by motorists and bicyclists. The results were developed from an analysis of observations of bicyclists and motorists interacting on different types of roadways. The evaluation included roadways with wide curb lanes, bicycle lanes, and paved shoulders. Locations from both rural and urban environments were included and varied in terms of motor-vehicle speed, traffic volume, lane width, and number of lanes. The operational measures of effectiveness used in evaluating the different types of facilities included (a) lateral placement of the bicyclist, (b) lateral placement of the motor vehicle, (c) separation distance between the bicycle and the motor vehicle, and (d) encroachments by the motorist or bicyclist during the passing maneuver. Results of the analysis showed that the type of facility (wide curb lane versus bicycle lane versus paved shoulder) does have a significant effect on the separation distance between bicyclists and motor vehicles; this distance ranged from 1.80 to 1.95 m (5.9 to 6.4 ft). The findings also indicated that paved shoulders and bicycle lanes generally result in similar interactions between motorists and bicyclists and that when compared with wide curb lanes they offer some distinct advantages to both user groups. The results also indicated that bicycle lanes as narrow as 0.92 m (3 ft) provide sufficient space for motorists and bicyclists to interact safely. At the same time, a 1.22-m (4-ft) wide bicycle lane tended to optimize operating conditions because there were very few differences in the measures of effectiveness when 1.22-m lanes were compared with wider lanes.

Evaluation of Blue Bike-Lane Treatment in Portland, Oregon

Many European cities use colored markings at bicycle–motor vehicle crossings to reduce conflicts. To determine whether such colored markings help improve safety at American bicycle–motor vehicle crossings, the city of Portland, Oregon, studied the use of blue pavement markings and a novel signage system to delineate selected conflict areas. The University of North Carolina Highway Safety Research Center (HSRC), under contract to FHWA, analyzed the project data. From 1997 to 1999, Portland marked 10 conflict areas with paint, blue thermoplastic, and an accompanying “Yield to Cyclist” sign. All of the sites had a high level of cyclist and motorist interaction, as well as a history of complaints. The crossings were all at locations where the cyclist travels straight and the motorist crosses the bicycle lane in order to exit a roadway (such as an off-ramp situation), enter a right-turn lane, or merge onto a street from a ramp. The study used videotape analysis and found most behavior changes to be positive. Significantly higher numbers of motorists yielded to cyclists and slowed or stopped before entering the blue pavement areas, and more cyclists followed the colored bike-lane path. However, the blue pavement also resulted in fewer cyclists turning their heads to scan for traffic or using hand signals, perhaps signifying an increased comfort level. The overwhelming majority of cyclists and close to a majority of motorists surveyed felt the blue areas enhanced safety. Colored pavement and signage should continue to be used and evaluated in bicycle–motor vehicle conflict areas.

THREE-STRAND CABLE MEDIAN BARRIER IN NORTH CAROLINA: IN-SERVICE EVALUATION

By using historical crash data, several regression-type models were developed with which to estimate the effects of the installation of cable median barrier on crash rates for several crash types while taking into account several other factors associated with variation in crash occurrences or crash rates. The data for these analyses consisted of counts of crashes of the various types for each section of North Carolina Interstate highway, along with the associated roadway characteristics, for 1990 through 1997. Certain roadway characteristics (in particular, traffic volume) changed from year to year as, of course, did the crash counts. The entire North Carolina Interstate system was taken as a reference population; a negative binomial error structure was assumed for many of the models, and the models contained specific effects for each crash year to account for various unmeasured effects that may vary from year to year (e.g., weather conditions). These models used the reference population to predict numbers of crashes on the cable sections. After cable barrier installation, none of these crashes occurred. In summary, these analyses indicate that several types of crashes (e.g., ran-off-road-left, hit-fixed-object) increased on the sections where cable median barrier was installed. However, these sections showed improved overall safety through fewer serious and fatal crashes as well as fewer head-on crashes. Overall severity index values were greatly reduced after cable barrier installation.

EXAMINATION OF FAULT, UNSAFE DRIVING ACTS, AND TOTAL HARM IN CAR-TRUCK COLLISIONS

Crashes involving large trucks and passenger cars are important topics for research and countermeasure development since they represent more than 60% of all fatal truck crashes and because the passenger car occupant is much more likely to be killed. This study (a) examined “fault” in total car–truck crashes using North Carolina Highway Safety Information System (HSIS) data for comparison with fault analyzed in previous studies of fatal crashes, (b) used general estimates system (GES) crash data to verify unsafe driving acts (UDAs) identified by expert panels in past studies, and (c) used North Carolina HSIS data to identify critical combinations of roadway facility type, roadway location, and crash type based on “total harm”—a measure combining both the frequency and severity of the crash. Fault in total North Carolina car–truck crashes was found to differ significantly from past fatal crash studies, with the truck driver being at fault more often than the car driver both overall and in certain crash types. Car drivers continue to be at fault much more often in head-on and angle crashes. While it was not possible to analyze all UDAs identified in prior studies, when possible, the current analyses revealed differences between the GES crash data results and the expert-based results, pointing to the need for better UDA methods if they are to be used to target treatments. Finally, using the total-harm analysis with North Carolina car–truck crashes indicated that undivided rural arterials and collectors should be primary targets for further investigation and for treatment.

Evaluation of Truck Crashes Using a GIS-Based Crash Referencing and Analysis System

Computerized crash analysis systems in which crash data, roadway inventory data, and traffic operations data can be merged are used in many states and municipalities to identify problem locations and assess the effectiveness of implemented countermeasures. By integrating this traditional system with a geographic information system (GIS), which offers spatial referencing capabilities and graphical displays, a more effective crash analysis program can be realized. In a recent FHWA-sponsored study, a crash referencing and analysis system within a GIS was developed within the Highway Safety Information System (HSIS) of the state of North Carolina for the area of Wake County. The system provides the functions needed to edit both tabular and spatial crash and roadway data as well as to perform crash analyses related to intersections, roadway segments, and special highway features, such as bridges. The second phase of the project was undertaken to illustrate the advantages of a GIS-based crash analysis system. The problem selected was identifying and analyzing locations of high numbers of truck-crashes, both along designated truck corridors and on other roadways within the county. The goal of the study was to determine if there are benefits to using a GIS-based crash referencing system over the traditional databases that contain crash, roadway feature, and operations data files and can be linked by location. Specific objectives for the truck-corridor analysis project included (a) identifying locations of high numbers of truck crashes using the GIS-based system, and (b) exploring the applicability of nontraditional databases to this type of analysis.

Observational Analysis of Pedestrian, Bicyclist, and Motorist Behaviors at Roundabouts in the United States

Roundabouts continue to gain popularity in the United States as an intersection treatment for improving operational efficiency and motor vehicle safety. A number of studies conducted in the United States and other countries have shown the benefits of roundabouts for these purposes. However, there is still concern that roundabouts may not provide safety or operational benefits for pedestrians and bicyclists. Crash-based studies of pedestrian and bicyclist safety in the United States have fallen short because of the relatively small number of roundabouts installed to date, which results in sample size issues due to the low number of motor vehicle collisions involving pedestrians and bicyclists. This study was undertaken as part of an NCHRP project. This paper focused on analyzing the interactions between motorists and pedestrians or bicyclists at roundabouts. This research did not find any substantial safety problems for nonmotorists at roundabouts based on conflicts or collisions. At the same time, the findings from behavioral observation have highlighted some aspects of roundabout design that require additional care to ensure safe access for pedestrians and bicyclists. Emphasis needs to be placed on designing exit legs to ensure proper sight lines and motor vehicle speeds. The junction of the circulatory lane and exit lane was observed to be the location of greatest risk for bicyclists. Multilane roundabouts may require additional traffic control measures to ensure safe access for pedestrians.

Operational Characteristics of Longer Combination Vehicles and Related Geometric Design Issues

As the size and configuration of trucks operating on public highways continues to change, how these vehicles operate needs to be better understood to accommodate them through better geometric designs or regulate them through more stringent laws and better enforcement. Longer-combination vehicles (LCVs), a group that includes Rocky Mountain doubles, turnpike doubles, and triples, fall into this category. LCVs handle and perform differently from tractor semitrailers or twin trailers because of their increased lengths and weights. These differences in handling and performance may jeopardize the safety of the LCV as well as other vehicles on the roadway. Several of the LCVs operational characteristics are believed to have an impact on transportation safety and the relationship of these characteristics to geometric design. There is a clear need to conduct additional research to further evaluate LCV operations. Several such research efforts are recommended.

Evaluation and Validation of Automated In-Vehicle Data Collection System for Developing Roadway Alignments

The Highway Safety Information System (HSIS) sponsored by FHWA includes crash and roadway inventory data from nine states for conducting safety studies. Whereas the initial choice of participating states was based on the presence of key roadway inventory variables, only two of those states currently have horizontal curvature data, and the data are limited. Given the known relationship between roadway curvature and safety, an objective of recent HSIS research was to improve on the available curvature data. A new algorithm makes use of in-vehicle data collected at highway speeds for the development of roadway alignments. Analysis of the algorithm focused on both consistency and accuracy. By using the Connecticut Department of Transportations automatic road analyzer vehicle, repeated runs were made in both directions on each route selected for the consistency analysis. For the accuracy analysis, horizontal alignments were determined on the basis of survey data collected at the same locations. In general, the results from the PLV-HC software, which uses the azimuth data from the automated vehicle, prove that the data can be used to do a good job of identifying curves and tangents on a roadway. However, the data collected and the postprocessing software need improvement to capture the radius and length of each curve more consistently and accurately.

Development of an Intersection Prioritization Tool for Accessible Pedestrian Signal Installation

Although increased complexity in intersection design and signal timing has improved intersection service to vehicle traffic, it has created additional challenges to pedestrians who are blind or who have low vision. Safe and independent crossings for pedestrians who are blind or who have low vision may require installation of accessible pedestrian signals (APSs) at some complex signalized intersections. APSs provide an audible and sometimes a tactile indication when the walk signal is on to cross the street. The goal of this study was to create a tool to prioritize locations for the installation of APS. To develop the prioritization tool, various characteristics of the intersection and the individual crosswalk were assigned point values that indicated their relative effect on the need for an APS at the crosswalk. For example, a point is assigned if the crossing is interrupted by a median; two points are assigned if there is a channelized turn lane. Field tests were conducted in which sites were ranked in o...