Roadside Encroachment Database and Analysis (2025)
Chapter: 1. Introduction
1. Introduction
1.1 Research Problem Statement
The research problem statement, as outlined in the Statement of Work for the project, is quoted below:
Run-off-road (ROR) traffic crashes account for almost one third of the deaths and serious injuries each year on U.S. highways. The 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. The age of these datasets means they are likely no longer representative of the current vehicle fleet or highway conditions. Further, each of these datasets 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); such limitations have fostered much debate over the value of findings from these studies.
Immense progress has taken place 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 roadside encroachment data across the range of traffic volumes and vehicle types.
There is a critical need to collect new roadside encroachment data to understand the frequency and nature of encroachments across the entire vehicle fleet. These data may inform the refinement of current crash testing procedures in the Manual for Assessing Safety Hardware (MASH; AASHTO 2016) and facilitate updates to the Roadside Design Guide (RDG; AASHTO 2011) and potentially the Highway Safety Manual (HSM; AASHTO 2010).
1.2 Objectives and Scope
The objectives of this research project are to (1) develop a database of roadside encroachment characteristics for a variety of roadside conditions and roadway types and (2) analyze the database to evaluate (a) the effects of the characteristics on the nature and frequency of roadside encroachments, (b) the relationship between unreported and reported crashes, and (c) whether heavy vehicle, bus, and motorcycle encroachments resulting in a crash differ from passenger vehicle encroachments resulting in a crash.
Development of the database should address the following roadside encroachment characteristics, at a minimum:
- Pre-encroachment conditions;
- Cross-sectional elements;
- Rural vs. urban;
- Urban curbed vs. uncurbed;
- Vehicle type;
- Various traffic volumes and speeds;
- Horizontal and vertical alignments;
- Levels-of-service; and
- Number of lanes, lane width, and access density.
Further, the database development should address the following roadside encroachment outcomes, at a minimum: reported and unreported; intentional and unintentional; tracking vs. non-tracking; runoff distance; vehicle trajectory; and crash severity.
