TTI Research Supervisor:
Chiara Silvestri Dobrovolny, Ph.D.
Associate Research Scientist
Texas A&M Transportation Institute
College Station, Texas 77843-3135
(979) 845-8971 [email protected]
Pooled Fund Technical Representative:
Washington State Dept of Transportation
310 Maple Park Avenue
P.O. Box 47329
Olympia, Washington 98504-7329
(360) 705-7952 [email protected]
A general problem occurs at many bridge locations along highways where the required length of need for bridge approach rails cannot be met within the existing right-of-way limits. These conflicts occur when existing driveways, roads, or other objects are within the ROW. It is not unusual to have less than 15 ft length between the end of the bridge and conflict. Solutions to this problem have included using short radius guardrail, a shortened guardrail section, or a crash attenuator. Typically, these solutions are not practical for the site location or are not cost effective.
The purpose of the study is to identify the best practices used to alleviate problems where length-of-need requirements for bridge approach rails cannot be met. The guide document was developed through a literature review and survey of State DOTs. The survey addressed data concerning: practices or standards for bridge barriers when LON cannot be met, practices variation according to design speed, different types of crash cushions used, and installation of a short radius guardrail in front of a slope.
From the information collected, it appears that use of short radius guardrail practice at bridge locations where LON cannot be met is generally the option preferred by the DOTs. Although few States indicated that their DOTs make somewhat frequently use of crash cushions at bridge locations where LON cannot be met, their employment is very limited by other States due to their higher installation and maintenance costs. Also, use of crash cushions might become not practical and undesirable on road sections with multiple drives and side roads, considering their size.
Some State DOTs prefers to relocate the obstacle/ drive access to a point beyond the proposed length of need. When that is not feasible, DOTs have different preferences on how to shield the obstacle, which includes use of short radius guardrail, crash cushions, but also Wood Post Controlled Release Terminal (Alaska DOT), T-Intersection or adjustment of the LON equation (Louisiana DOT), and nested thrie beam transition from concrete bridge rail end block, then attachment of short radius rail as necessary (South Dakota).