Most operational guardrail systems in the United States have been developed to contain a 4,500-lb vehicle impacting at 60 mph and 25 deg. The use of design criteria based on these test conditions has resulted in relatively expensive guardrail installations. For low-service-level roads, there is a need to determine the conditions under which less stringent guardrail requirements are warranted in order to avoid excessive expenditures and provide safety performance based on demonstrated need.
Four low-service-level barrier systems were developed under NCHRP Project 22-5 to address this need. Through full-scale crash testing, these systems were shown to contain a 3,400-lb vehicle impacting at 50 mph and 20 deg. It is anticipated that these barriers can be used to improve the level of safety on low-service-level roads; however, correlation of the crash test conditions with field conditions is required. In addition, a user's guide is needed to provide design details for the systems developed and specific warrants for their placement on low-service-level roads.
The objectives of NCHRP Project 22-5A are to develop warranting procedures for the placement of the barrier systems developed under NCHRP Project 22-5, and to prepare a user's guide which contains design drawings for these systems and warranting procedures for their placement.
This research shall include at least the following tasks:
Task 1---Determine the range of roadway characteristics for which it would be appropriate to install the barrier systems designed and crash tested under Project 22-5. In addition, estimate the installed cost for each of these barrier systems. A letter report containing the findings of this task shall be submitted to NCHRP. Panel approval of the letter report is required before proceeding to Task 2.
Task 2---Using the findings of Task 1, develop specific warranting criteria for the placement of the barrier systems developed under Project 22-5. The product to be delivered by this effort will be warranting procedures in table and/or chart form to guide the placement of these low-service-level barrier systems.
Task 3---Prepare a user's guide which contains the warranting procedures developed under Task 2 and design drawings for the barrier systems developed under Project 22-5. The guidelines shall also include estimated life-cycle cost data for each barrier system.
Task 4---Prepare a final report documenting the research conducted under NCHRP Projects 22-5 and 22-5A.
A condensed version of the report has been published as NCHRP Research Results Digest 194, and loan copies of the full final report are available from NCHRP.