Safety Performance of Part-Time Shoulder Use on Freeways,” was todevelop models and other quantitative tools for practitioners to evaluate safety performance of freeways with part-time shoulder use (PTSU) (including Bus on Shoulder (BOS)). The research is complete; it produced models that predict (1) the frequency of fatal-and-injury (FI) crashes and (2) the frequency of property damage only (PDO) crashes. These models were applied to assess the overall effect of PTSU on total and severe crash frequency. Models are available for basic freeway segments, entrance speed-change lanes, and exit speed-change lanes. A severity distribution function (SDF) also was developed to predict the distribution of FI crashes among different severity levels. Each model includes variables that describe the traffic demand characteristics, geometric elements, and PTSU operational features.
This continuation request will support pilot testing of the PTSU models developed in Project 17-89 by state DOTs that operate such facilities with the goal of determining whether additional resources are needed to support wider-scale implementation through HSM2. The pilot tests will provide material for one or more case studies that will help practitioners use the research products. In addition, review of the pilot states’ efforts will help identify anyHighway Safety Manual (HSM)-related needs, such as text to be included with the models, text for other sections of the HSM to explain the relationship to other models, training materials, etc. Subject to the availability of data, the participating state DOTs will run the models to:
1. Estimate FI and PDO crash frequencies, compare them to DOT experience, and evaluate whether the models are suitable in their present form for incorporation in HSM2.
2. Evaluate differences in safety performance between right- and left-side PTSU.
3. Conduct a before-after study of freeways where PTSU was implemented during NCHRP Project 17-89.
Tasks to be performed include:
Task 1. Review the NCHRP Project 17-89 research results to: (a) identify potential challenges to pilot testing, (b) determine the need for state calibration of the models, and (c) identify two to five agencies with data suitable and sufficient for pilot testing; these may include agencies whose data was used in the model development and those whose data was not.
Task 2. Based on the results of Task 1, provide technical support to the agencies with roadway sections with PTSU to (a) conduct pilot testing of the models, (b) compare the model results to the agencies’ experience of FI and PDO crashes on these sections, and (c) if suitable data are available, compare right- and left-side PTSU and before and after PTSU safety performance.
Task 3. Submit a final report that presents the results of the pilot testing and includes (a) one or more case studies of use of the models, (b) a recommendation for the suitability of incorporating the models in HSM2 in their present form, and (c) any additional resources needed to support wider-scale model implementation through HSM2.
Task 4. Present a webinar that discusses the pilot tests, the lessons learnt, and the way forward.
