BACKGROUND
Each year, roadway departure crashes in the United States result in serious injuries and fatalities. Side impacts of vehicles into roadside hardware are a growing public safety problem. In particular, side impacts with guardrail account for a significant percentage of fatalities in passenger vehicle-guardrail crashes.
An occupant of a passenger vehicle that side impacts with guardrail has a 30 percent higher probability of fatal injury than an occupant of a car that frontally impacts with guardrail. Many roadside safety features, such as terminals, guardrail end treatments, crash cushions, and luminaire and sign supports, are designed to break away under typical loads for a frontal impact. However, side impacts by non-tracking vehicles may not have enough force to engage the breakaway mechanisms of these features. Because the side of a vehicle, unlike the front, has less structure and crumple zone, side impacts can result in especially severe injuries.
To date, however, no substantive improvements have been made to the performance of roadside safety features during vehicle side impacts. NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features provided information on side impacts through test and evaluation procedures; however, it does not contain recommendations or requirements for side impact crash testing of roadside safety hardware (RSH). More recently, the NCHRP Report 350 appendix for side impact test and evaluation procedures was not included in the AASHTO Manual for Assessing Safety Hardware (MASH) crash test procedures. Little is known about how NCHRP Report 350- or MASH-compliant hardware performs in side impact crashes.
No research to date has developed a comprehensive approach for evaluating RSH under side impact conditions. The development of methods for evaluating these crashes would lead to improvements in RSH and improved safety for motorists. Results of this research could enable transportation agencies to establish levels of safety risk and use quantitative information to do so.
Under NCHRP Project 22-32, “Development of Methods to Evaluate Side Impacts for Next Edition MASH,” work began to develop this comprehensive approach and produced a report describing the following:
- Recommended test procedures for evaluating RSH under side impact conditions;
- Plan for validating two aspects of side impact performance: ability of side impact design improvements to lower occupant risk and translation of lower occupant risk to fewer severe and fatal injuries in side impact crashes observed in the field;
- Preliminary recommendations for consideration by AASHTO in future updates of MASH and Roadside Design Guide (RDG); and
- Work plan for side impact crash testing and finalizing side impact test procedures and evaluation criteria, with optional side impact crash testing of luminaire supports and shallow-angle corner impacts on guardrail.
The crash testing, however, was not conducted, hence the need for additional research, with the intention of this testing to include luminaire supports and shallow-angle corner impacts on guardrail.
OBJECTIVES
The objectives of this research are the following:
- Determine appropriate values for RSH performance criteria, building on previously developed test procedures; and
- Develop an evaluation guide for RSH under side impact conditions.
This research shall consider appropriate test vehicles and focus on terminals; however, it shall also consider additional roadside safety devices.
RESEARCH TASKS
Task 1. Review previous work and literature; recommend updates to work plan.
Task 1a. Review previous work and literature. Review work completed under NCHRP Project 22-32 (see Special Note A). Conduct a literature review to identify any additional research findings or other technical progress pertinent to the project.
Task 1b. Recommend updates to work plan. Based on the findings of Task 1a, recommend any changes felt necessary to the work plan, providing justification. Submit the findings of Task 1a and the updated work plan to NCHRP for approval. NCHRP approval is required before work on Task 2 can begin.
Task 2. Conduct crash testing. Evaluate the procedures recommended under NCHRP Project 22-32 and confirmed in Task 1 for measuring occupant risk factors in side impacts. The testing shall include the following objectives:
a. Demonstrate repeatability of the side impact testing;
b. Determine the performance of current guardrail end terminals;
c. Determine the performance of luminaire poles; and
d. Evaluate the vulnerability of current guardrail end terminals to shallow angle impacts.
The research team shall ensure that (a) critical MASH Test Level 3 vehicles are considered in the testing; (b) MASH guardrail end terminals are used in the testing; and (c) confidentiality shall be maintained for any proprietary hardware tested, e.g., by categorizing performance issues by nature rather than by specific device characteristics.
Following the testing, the team shall submit an interim report summarizing Task 2 results for NCHRP approval. The team shall also present a summary of Task 2 results at an in-person meeting with NCHRP. NCHRP approval of the interim report is required before work on Task 3 can begin.
Task 3. Analyze test results. From Task 2 results, determine the practicality of the evaluation criteria and how agencies would implement them. Develop an annotated outline for an evaluation guide. Submit the analysis and guide outline to NCHRP for approval via technical memorandum. NCHRP approval of the memorandum is required before Task 4 can begin.
Task 4. Develop evaluation guide and related documentation.
Task 4a. Develop evaluation guide. Elements for the guide shall include technical considerations for public or private organizations conducting the evaluations and implementation considerations for stakeholders, e.g., modifying MASH guidelines.
Task 4b. Develop draft language for consideration by AASHTO to incorporate the research results in future MASH and RDG editions. This language shall be presented in the appropriate style following the MASH and RDG formats.
Submit a technical memorandum summarizing the results of Task 4 for NCHRP review. NCHRP approval of the memorandum is required before Task 5 can begin.
Task 5. Submit final report and evaluation guide. Submit a final report documenting the entire research effort; the evaluation guide; and the draft language for the AASHTO documents.
STATUS: Research in progress.
