Barrier height reduction with asphalt overlays
Cast-in-Place Barriers
Cast-in-Place Barriers
Patrick O'Neill
Washington
Barrier height reduction with asphalt overlays
If a 32” single slope or Type F barrier were to be built as TL-3, then a 2” overlay employed making the reveal height 30”, does this barrier then get downgraded to TL-2 due to height being less than 32” (absent MASH crash tests)? Current AASHTO guidance C13.7.3.2 allow overlays, but it seems to be based on NCHRP Report 350 testing.
Nauman Sheikh ( [email protected]) Texas A&M Transportation Institute
For the F-shape, New Jersey, and Single Slope profiles, there is a tendency of the vehicle to climb upwards because of the sloped face of the barrier. These barrier shapes have not been tested at a 29-inch effective height, and therefore, their performance is not known based on MASH testing.
The 29-inch minimum height is likely okay for a vertical parapet based on the simulations performed under NCHRP 20-07(395). However, this may not be applicable for all longitudinal barrier designs and shapes.
To illustrate the above, please see the roll of the pickup when tested with 32-inch tall vertical parapet (attached. Source: NCHRP Project 22-20, NCHRP Report 663). The pickup had about 40-degree roll with the 32-inch tall vertical parapet. If the height of this parapet is reduced to 29 inches, the roll and vehicle instability is likely to increase further and make it marginal. If the height is reduced to 29 inches, and the barrier has an F-shape profile, the instability is likely to increase further and there is greater chance for a rollover.
In summary, the performance of a 29-inch tall F-shape or single slope barrier is likely to be marginal in terms of roll with a possibility of a rollover. For this reason, we cannot conclude that it would be MASH compliant without performing a crash test.