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Agencies are seeking a better understanding of those roadway or roadside features that affect safety. The objectives of this study were to develop a horizontal curve accident modification factor (AMF) for rural four-lane divided and undivided highways and to determine if the effect of driveway density is different for horizontal curves as compared to tangent sections. Data available for use in the evaluation included 194.8 centerline km (121 centerline mi) of rural four-lane highways. Negative binomial regression models were used to determine the effects of independent variables on crashes. Variables considered in developing the base models included driveway density, lane width, outside shoulder width, median width (which included inside shoulder width), median type, degree of curve, segment length, and average daily traffic. Five years (1997-2001) of driveway and segment crashes were examined. An AMF for horizontal curves was identified. Reviewing the findings with respect to driveway density revealed that the effect of driveway density is different for horizontal curves and tangents; however, the differences were relatively minor. DOI: 10.1061/(ASCE)TE.1943-5436.0000145 CE Database subject headings: Traffic accidents; Highways and roads; Statistics; Texas; Rural areas. Author keywords: Traffic accidents; Roads; Statistical analysis.

Right-turn lanes are used to provide space for the deceleration and storage of turning vehicles and to separate the turning vehicles from the through movement. When larger corner radii are used at the right turn, vehicles can turn at higher speeds (thereby minimizing speed differential between turning and through vehicles). A concern with the higher operating speed is the challenge it provides pedestrians. This project analyzed the impact of right-turn treatments on right-turn vehicles speeds at 19 urban approaches. Each approach had an exclusive right-turn lane that was separated from the through lane with either a lane line or a raised corner island. The 85th percentile free-flow speed near the middle of the right turn ranged from 20.9 to 33.8 km/h (13-21 mi./h) while on the approach it ranged from 27.4 to 46.7 km/h (17-29 mi./h). Speed prediction equations were developed as part of this study. CE Database subject headings: Traffic speed; Statistics; Urban areas; Predictions.

The transportation profession is seeking to better understand the features that influence roadway speeds. Engineers need an appreciation of which roadway design features, or the values for the features, clearly relate to the speed performance on a facility. This study utilized free-flow speed data collected at 79 tangent sites in suburban/urban and rural areas in seven cities located in six states. Key variables used to select sites included functional classification (arterial, collector, and local), edge treatment (curb and gutter versus shoulder), and speed limit. Technicians collected speed data at the midpoint of long straight sections during daylight conditions. For each site, roadway and roadside characteristics were collected such as number of access points within the study section, roadside development type, lane width, and others. Statistical testing revealed that posted speed limit was the only statistically significant variable at a 5% alpha level. Access density was next with an approximate 20% alpha level. Several variables other than posted speed limit and access density showed signs of influence on the 85th percentile free-flow operating speed, including: median type, parking along the street, and pedestrian activity level. A followup cluster analysis revealed the following noteworthy features: pedestrian activity, parking, centerline, median treatment, roadside development, area type, and signal density. CE Database subject headings: Traffic speed; Traffic management; Roads; Statistic analysis; Pedestrian traffic flow; Parking.

The relations between certain inappropriate driving behaviors and the increasing number of vehicular accidents is studied. Research in the form of telephone interviews and surveys were conducted at Pennsylvania State University to establish the link between irrational driving behavior and motor vehicle accidents. It was found that a large number of accidents were caused by driving errors, such as tailgating or driving in the wrong lane. The results also indicate that males are more prone to vehicular accidents than females.

Several driving behaviors with a high potential for causing accidents are presented to illustrate the unreliability of traffic citations as indicators of noncompliance with traffic laws. These extreme situations underscore the limitations of compliance with the law in preventing traffic accidents. Moreover, these illustrate a need for educational safety programs that stress not only compliance with the law but also awareness of results of certain driving behavior.