Converging chevron pavement markings have recently seen rising interest in the United States as a means to reduce speeds at high-speed locations and improve safety performance. This paper reports on an investigation into the effectiveness of chevron markings in reducing vehicle speeds on two-lane freeway-to-freeway directional ramps in Atlanta, Georgia. The evaluation is based on a statistical comparison at preselected sites of speeds before and after the installation of the chevron markings. The analysis focuses on the effect of converging chevrons over the range of speed percentiles and on the mean speed. The analysis indicates that chevrons have a minimal effect on vehicle speeds, with drivers adjusting back to their previous speeds as they acclimate to the treatment. The effect of the chevrons’ treatments on speed tended to be most pronounced immediately after the chevron implementation. However, by the 9th month after implementation the magnitude of the effect dropped to under 1 to 2 mph for the mean speed and most vehicle speed percentiles. Although this result does not necessarily imply that the chevron treatment is not a meaningful safety treatment, any safety benefits are not likely to result from a general decrease in speeds.

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Roadway sections that experience a higher-than-expected number of crashes are usually identified by long-term crash frequency data. When historical crash data are either limited or unavailable, surrogate safety measures based on roadway characteristics (e.g., road geometry, traffic volume, and speed) are often substituted. This study developed and evaluated several candidate measures to estimate crash frequency on urban streets on the basis of speed consistency along the roadway. These speed consistency measures were based on speed profiles along road segments collected from vehicles equipped with Global Positioning System (GPS) devices. The relationships between these surrogate measures and historical crash frequency were quantified with the use of a combination of regression tree and generalized linear modeling approaches. The findings support the use of the profile-based measures to evaluate the safety of road networks as the deployment of GPS-equipped vehicles becomes more prevalent.

Acceleration and deceleration characteristics are basic driving behaviors that influence signal control and road geometry. Most previous studies focused on acceleration and deceleration rates under ideal conditions, i.e., on characteristics of lead vehicles, which might not adequately reflect the full spectrum of traffic operations. This paper presents a methodology for determining acceleration and deceleration rates and zone lengths for vehicles approaching and leaving intersections under likely uncongested traffic conditions, regardless of queue position. These characteristics are derived from speed profiles gained from vehicles equipped with Global Positioning System (GPS) instrumentation. With the speed profiles obtained from GPS-equipped vehicles, a series of data-processing algorithms is developed to measure the acceleration and deceleration behavior of vehicles approaching and departing an intersection. Acceleration and deceleration rates and zone lengths are estimated for several road categories. These zone lengths are compared with recommended values from AASHTO's A Policy on Geometric Design of Highways and Streets (Green Book), in which it is seen that the zone lengths under light traffic conditions are longer than the Green Book's values. In addition, determined acceleration and deceleration rates and zone lengths are found to depend on the underlying assumptions and calculation methods of the analysis.

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