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Situation:

An existing bridge has a 32"Jersey Shape rail similar to this. An overlay of 5" is proposed and an extension of 5" to the top of the barrier is the proposed solution.

Question:

What effect does covering up the 3" lip at the bottom have on the barrier working as designed?

Any other concerns?

Covering up the 3" reveal has been shown to improve the safety performance of Safety Shaped Barriers. Recently, we developed several concepts for the cross-sectional geometry of the new TL-5 median barrier. We are proposing to use a vertical face barrier in order to reduce the propensity for vehicular instabilities which may occur during an impact event with the barrier system. Based on our review of the historical crash test data with small cars and pickup trucks, the vertical parapet geometry has proven to provide the lowest potential for vehicle climb and roll angles as compared to those observed in impacts into the New Jersey shape, F-shape, and single slope barriers. Therefore, it is our opinion that the propensity for vehicle rollover can be decreased by minimizing barrier climb and vehicle roll angle during barrier impact events. Thus, the elimination of the 3" lip will improve the performance of the barrier as it will in effect make the barrier closer to a vertical shape.

In addition, as part of the initial investigation, numerous crash test videos were analyzed in order to determine a head ejection envelope corresponding to a 50th percentile male dummy seated in either the driver-side or passenger-side seats of both small cars and pickup trucks. Using the head ejection data, the barrier's proposed top geometry was setback or stepped in order to prevent an occupant's head from impacting the barrier surfaces as it is potentially ejected out a side window during an oblique barrier impact. Additionally, based on the head ejection envelope, we determined that no issues with head ejection were present for barriers below 35" in height.

Therefore, we can conclude that providing a 5" overlay and a 5" extension will only improve the performance of the safety shape. This of course assumes that the 5" extension has sufficient capacity to handle the barrier impact loads.