Traffic barriers that can resist vehicle impact without being tied to a structure are needed at the top of mechanically stabilized earth walls. These barriers are usually constructed in an L-shape so that the impact load on the vertical part of the L can be resisted by the inertia force necessary to uplift the horizontal part of the L. The design load for such barriers has changed from 44.5 kN (10 kips) to 240 kN (54 kips) over the past decade. This increase has created concern about which load should be used. This paper contributes to answering that question. It shows the results of analytical solutions to the problem as well as one static load test and two impact tests on the same full-scale barrier. The conclusions are that 44.5 kN (10 kips) is an equivalent static load and that the 240 kN (54 kips) is a peak-impact load. Analytical and experimental approaches are used to provide better understanding of the behavior of the barrier-moment slab system. Guidelines for the dimensions of the barrier-moment slab system are presented and justified on the basis of the work described.