Guardrail Posts on Mowstrips (405160-14)

Final Report Link: Alternative Design of Guardrail Posts in Asphalt or Concrete Mowing Pads

TTI Research Supervisor:
Roger P. Bligh, Ph.D., P.E.
Texas Transportation Institute
Texas A&M University System
TAMU 3135
College Station, Texas 77843-3135
(979) 845-4377
[email protected]

Pooled Fund Technical Representative:
Paul Fossier, P.E.
Louisiana Department of Transportation
P.O. Box 94245
Baton Rouge, LA 70804-9245
(225) 379-1323
[email protected]

ABSTRACT:

In an effort to reduce maintenance costs and the safety risk to workers associated with hand mowing around guardrail, and amid recent environmental concerns regarding the use of herbicides to control roadside vegetation growth, there is a growing trend toward encasing guardrail posts in pavement mow strips. However, if not properly designed, a mow strip can negatively influence the impact performance of a guardrail system.

The Texas Department of Transportation (TxDOT) sponsored research at the Texas Transportation Institute (TTI) to develop a crashworthy means of encasing guardrail in an asphalt or concrete mowing strip. The recommended design includes provision for a “leave-out” area in the mow strip around the guardrail post that is backfilled with a low-strength grout mix that resists vegetation growth but is weak enough that it crushes under loading from the guardrail post during a vehicular impact.

The objective of this project was to identify alternative backfill materials for the low strength grout mix. Static laboratory and dynamic bogie impact testing was conducted to evaluate several products for use around guardrail posts encased in a pavement mow strip. The products that were found to be acceptable include a two-part urethane foam, a molded rubber product that has an insert fabricated to match the size of the leaveout, and a pop out concrete wedge conceived under the project. Each of these products has its own advantages and disadvantages in terms of cost, availability, ease of inspection, and installation. It is recommended that some field experience be gained with these products to better assess which would provide the most cost-effective solution for a particular user agency.