Run-off-road (ROR) traffic crashes account for almost one-third of the deaths and serious injuries each year on US highways. Effective design of roadsides, including the placement of roadside safety devices, can reduce the frequency and/or severity of these crashes but requires an understanding of the nature and frequency of roadside encroachments. Unfortunately, the best quality encroachment data currently available were collected in the 1960s and 1970s and only for passenger vehicles. The age of these data sets suggests that they are no longer representative of the current vehicle fleet or highway conditions. Furthermore, each of these data sets has significant limitations, including specific exclusion of heavy vehicles and motorcycles, and a very limited range of traffic volumes (i.e., less than 20,000 vehicles per day), that have fostered much debate over the present value of the data.
There is a critical need to collect new roadside encroachment data to understand the frequency and nature of encroachments across the entire vehicle fleet. There has been immense progress in both the development of new roadside safety devices and in the improvement of existing devices since the 1960s. Proper development, testing, and placement of these devices along the roadside, however, is required to maximize their effectiveness. The guidelines for development, testing, and placement of these devices rely heavily on provision of reliable roadside encroachment data across a range of traffic volumes and vehicle types.
This research will support the Technical Committee on Roadside Safety’s (TCRS) Strategic Plan. The plan’s objectives are to lead roadside policy development, support safety innovations, and identify standards that are outdated, lacking, or not supported by recent evidence within the current AASHTO Manual for Assessing Safety Hardware (MASH). Collection of new encroachment data will be used to refine current crash testing procedures as well as update the Roadside Design Guide (RDG).
The objective of this research is to develop a current understanding of roadside encroachments at a variety of traffic volumes and posted speeds across the entire vehicle fleet. Roadside encroachment data shall be collected for roadways with a range of ADT values and vehicle types. These data shall include the pre-encroachment conditions (e.g., on-road conflict, distracted driving, drowsiness) and highway characteristics, and will be used to study the need for the incorporation of buses and other heavy vehicles into various guidelines within the RDG, as requested by the National Transportation Safety Board (NTSB). The research shall collect both reported and unreported roadside encroachments that result in a crash and concurrently observe intentional and unintentional encroachments within identified sections of roadway.
Accomplishment of this objective shall require the following tasks, at a minimum: (1) conduct a literature review of existing and potential methods for the collection of encroachment data, including modern electronic surveillance techniques; (2) identify agencies willing to participate in this study through sharing their crash databases and road inventory data, and allowing the project team to monitor encroachments; (3) design a data collection procedure/system intended to monitor encroachments on a given roadway segment, including a cost estimate for implementing the procedure/system as well as the size of the expected encroachment database; (4) submit an interim report describing findings from Tasks 1-3 with a work plan for project completion; (5) collect encroachment data using the approved work plan in cooperation with participating agencies; (6) analyze the resulting encroachment database to determine (a) encroachment frequency for a range of traffic volumes, (b) how the encroachment frequency is impacted by the highway characteristics, including, but not limited, to horizontal and vertical alignments, Level-of-Service, number of lanes, lane width, access density, etc., (c) reported and unreported crash thresholds for various roadside hazards and features, and (d) if heavy vehicles, buses, and motorcycles encroach differently than passenger vehicles and should therefore be specifically addressed within the RDG and MASH crash testing procedures; and (7) prepare a final report that documents the entire research effort with recommendations for the refinement of the RDG and MASH.