As the nation’s roadway system becomes more congested and the number of vehicular crashes
increases, the importance of access management increases. Access management has been identified as one of the most critical elements in roadway planning and design; it has been defined as the process of managing access to land development while preserving the safety and efficiency of the surrounding roadway system. Access management helps to achieve the necessary balance between traffic movement and property access by carefully controlling the location, type, and design of driveways and street intersections. Highways are classified with respect to the level of access and mobility they are expected to provide, and then the most effective techniques to preserve those functions are identified and applied. The impacts of potential techniques on traffic performance and safety are important considerations when deciding which technique to implement.
Access management deals with the control and regulation of the spacing and design of medians, median openings, driveways, freeway interchanges, and traffic signals. Typical access management measures cover the type and design of medians and median openings; the location and spacing of intersections; the spacing and design of interchanges; and the location, spacing, and design of driveways and street connections. The location, the design, and the operation of driveways play a significant role in access management. According to the AASHTO Green Book, A Policy on the Geometric Design of Highways and Streets, driveways are considered at-grade intersections whose design should be consistent with intended use. However, the number of crashes at driveways is disproportionately high when compared to other intersections; thus, the design and the location of driveways merit special consideration.
The objectives of this research are (1) to quantify the effects of access management treatments on roadway operations and safety, and (2) to provide tools to evaluate access management treatments.
FINDINGS AND CONCLUSIONS
This project evaluated the safety and operational impacts of two alternative left-turn treatments from driveways/side streets. The two treatments were direct left turns (DLTs) and right turns followed by U-turns (RTUTs). Ten sites were selected for field data collection, and each site experienced one or both of the left turn alternatives from the driveway or side street. Video cameras were set up on scaffoldings to achieve adequate viewing height, and all of the traffic movements at the selected sites were recorded.
Safety analyses of the alternatives were conducted using two major approaches: traffic crash data analysis and conflict analysis. Operational analyses were conducted using empirical model development and simulation.
This project fulfills a long felt research need by traffic engineers, planners, and designers. The Florida Department of Transportation prohibits DLTs onto major arterials. However, regarding median closures at existing DLT locations, FDOT sometimes faces objections from the owners of commercial developments who prefer direct access. In addition, some drivers have expressed their concerns about the safety of U-turns in the RTUT process. The findings of this research provide FDOT with the quantified data to address such issues.
Results have indicated that under high volume conditions, RTUTs have beneficial effects both from the traffic operational and the safety fronts. For any selected location with similar characteristics, the volume cutoff point can be determined using the models developed in this study. If the actual volume is higher than this cutoff value, RTUT may be implemented by closing the full median opening or by making it directional and allowing only left turns to vehicles moving onto the driveway. This research showed that facilitation of directional median openings is more advantageous than full medians on high volume arterials with raised non-traversable medians. The findings also indirectly address the comparison between raised medians and two-way left turning lanes.