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Highway Safety Improvement Program National Scan Tour

Chapter 10–Evaluating the Success of the Program

By regularly evaluating their programs, States can continuously improve their strategies for achieving their SHSP goals and targets, as well as their own efficiency and effectiveness. Tracking and evaluating the effectiveness of completed HSIP projects is also a means to determine if those improvements are providing their predicted benefits. States with highly successful programs also "benchmark" themselves against other States, adopting new practices they find promising.

All States had developed some form of before-and-after project analysis. Alaska, Utah, Illinois, and North Carolina have strong evaluation programs that are being used to directly inform the development of safety performance functions (SPF), CRFs, and other values used in the screening and analysis portion of HSIP project development.


Safety Evaluations in North Carolina

The NCDOT Traffic Safety Unit conducts a Safety Evaluation for all completed safety projects. This evaluation includes project information, collision diagrams, and analysis of before and after crash frequency and severity. The analysis period is typically three years, but it can be extended for sites with a low pre-project crash rate. The Safety Unit executes roughly 120 safety project and program type evaluations each year and has trained consultant staff to perform evaluations in addition to in-house staff. Advanced evaluations are generally performed by NCDOT staff, such as the Empirical Bayes analysis of multiple sites.

There are three aspects to the NCDOT evaluation process. The first is NCDOT’s evaluation of every HSIP, Spot Safety, and hazard elimination project, a site-specific, simple before/after review of crashes. Headquarters provides the regions with the reports generated from these project-level reviews. (20)

The second is NCDOT’s Empirical Bayes evaluation of multiple site locations with similar countermeasure installations, which facilitates distinguishing between different treatments and the development of CMFs. The evaluations can be site-specific or taken across multiple similar sites. This was done for a variety of Intersection Cross-Road Warning System (ICWS) treatments and can be used to compare the effectiveness of varying treatment implementations.

The third aspect is a program-wide evaluation, undertaken program-wide for a Spot Safety or HSIP project. In the case of the Spot Safety program, NCDOT calculated a 14:1 b/c ratio for all improvements in the program across 600 projects.

One of the significant outcomes of NCDOT’s evaluation programs is the validation of CRF. NCDOT data collection efforts for projects, both prior to and subsequent to the construction of improvements, enables staff to conduct network-wide and site-specific evaluations of CRFs. This work, particularly with deployment of ICWS, has been crucial in preserving effective treatments for future implementations while permitting culling of less-effective treatments on the basis of location characteristics and countermeasure performance.

To that end, the NCDOT has developed an internal CRF list, covering roughly 260 countermeasures, and regularly correlates internal data with the FHWA CMF Clearinghouse. An in-house committee of technical experts performs the estimations of the CRFs, and the internal CRF lists are supported by the evaluations, all of which are included on the NCDOT web site.

The institutional establishment of this evaluation program and the various facets it encompasses has assisted NCDOT staff in retaining safety project funding and even obtaining increases in funding. The evaluation of project performance has also impacted other areas of NCDOT operations, leading to increased confidence in NCDOT investments.

HSIP Project and Program Evaluation and Monitoring

IDOT has not yet established a formal evaluation process. IDOT currently undertakes the evaluation of safety projects with three individual approaches.

Although they do not yet have a formal evaluation process, IDOT has informally evaluated safety projects at the programmatic, project, and systemic levels.

The Illinois Center for Transportation is conducting the three research projects, which focus on evaluation of the effectiveness of flashing yellow arrows, right-turn islands, and interchange improvements to prevent wrong-way movements. The Safety Technical Advisory Group within the Illinois Center for Transportation selected the research projects. The Technical Advisory Group solicits research proposals, and can also submit their own proposals. Research projects are selected based on what the Group perceives as priority research needs. For example, the SPFs used for statewide network screening and the basis for the SRI were selected by that group in 2007. It is important to note that if a researcher on the TAG submits a research topic proposal, they are not included in the review and approval of the project.

IDOT reviews the number of sites with implementation of countermeasures in order to determine which countermeasures to advance to evaluation in the research projects. Having a large sample size is important to obtaining system-wide before and after data. The research is reviewing the application of the strategies to over 100 intersections and over 400 interchanges. The results of the research projects will be used to develop State-specific CMFs and SPFs.

IDOT also conducts evaluations of experimental features when implementing new countermeasures. Doing so allows them to identify challenges, successes, and lessons learned, as well as develop policy based on what worked best. For example, when implementing cable rail, IDOT used different manufacturers on specific corridors so they could evaluate each type of system on its installation, maintenance, and by looking at crashes. They were then able to determine which types of cable rail to add to their approved products list. While the overall analysis of the cable rail was done as a corridor due to the fact that some segments may have not had any fatalities or injuries, but the corridor-wide data would show a different picture, the HSIP projects that came out of the analysis were done by funding segments.

The Alaska DOT&PF developed a methodology for demonstrating the effectiveness of HSIP projects. The Region Traffic Engineer prepares a Project Evaluation Worksheet for each project, evaluating the project based on 3-year post-construction data. The data is annualized for computation, and the cost of the project includes both the construction cost and the maintenance costs over the analysis period.

The Alaska DOT&PF evaluates projects based on 3-year post-construction data. They also use a program-wide b/c ratio to track performance of the overall HSIP.

The DOT&PF regions also use a project tracking report for HSIP that is turned into the Headquarters. The project report, which is separate from the HSIP Project Tracking Spreadsheet discussed in Chapter 9, evaluates targeted crashes for the before/after analysis and provides an overview of project performance. Incapacitating injuries are evaluated with fatalities to account for infrequency and isolation of crashes.

The DOT&PF has anticipated reductions in b/c ratios on account of the systemic approach that broadens applicability and breadth of a project, and these reductions are accepted as a result of the program’s initial effectiveness at addressing high-benefit locations. The b/c ratio for each project is calculated, when possible, and then aggregated to develop a program-wide b/c ratio, which is also an important metric of performance for DOT&PF.

CMF Development

UDOT uses 3-year before/after comparisons of completed projects to analyze the performance of every HSIP project. Utah has developed a State specific CMF registry, which provides discrete CMFs and serves as a resource for project planning and screening. UDOT applies only one CMF to the targeted crashes identified for each project as part of the b/c analysis. This practice eliminates the additive effects of CMFs and ensures reliable b/c projections.

Enforcement presence can have an effect on traffic safety and the Alaska DOT&PF is conducting a research project to develop a CMF for enforcement presence (another means of quantifying the benefit of enforcement expenditures), particularly in the Alaska Transportation Safety Corridors. The research effort would be primarily focused on time spent on enforcement, providing the basis for a cost associated with potential benefits.


All Host States have developed some form of before-and-after project analysis. Utah, Illinois, and North Carolina have strong evaluation programs that are being used to directly inform the development of SPF modifications, CRFs, and other values used in the screening and analysis portion of HSIP project development.

In both Alaska and North Carolina, each project is evaluated based on a standard evaluation form and methodology, using up-to-date crash data and measures of effectiveness appropriate for the countermeasures selected for use in the project. IDOT has an informal evaluation process that occurs at both the project and programmatic levels. In addition, IDOT is conducting research projects to evaluate system-wide safety improvements.

  1. North Carolina DOT. Safety Evaluation Group – Safety Evaluation Completed Projects. Available online at https://connect.ncdot.gov/resources/safety/Pages/Safety-Evaluation.aspx. Accessed February 24, 2016.
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