Roof crush resistance and rollover strength of a paratransit bus

Paratransit buses constitute a special group of vehicles in the US due to their smaller size, two-step assembly process, and their use for complementary services to the regular scheduled transit routes. Due to their uniqueness these buses lack national crashworthiness standards specifically dedicated to the paratransit fleet. Several states in the US adopted the quasi-static symmetric roof loading procedure according to the standard FMVSS 220 for testing the integrity of the paratransit buses. However, as many researchers point out, the dynamic rollover test according to UN-ECE Regulation 66 (ECE-R66), which was approved by more than forty countries in the world, (excluding the US), may provide more realistic assessment of the bus strength. This paper provides comparison of the numerically assessed strength of the paratransit bus according to the two standards in explicit FE simulations using LS-DYNA®/MPP. The FE model used in this study was previously validated through comparison of its simulated behavior with response of the bus in the full scale rollover test conducted at the Florida Department of Transportation testing facility (Tallahassee, FL, USA, 2010). The results show that the final assessment of the bus crashworthiness from both procedures can be divergent. Although the tested bus passes the quasi-static FMVSS 220 test, the same bus fails the dynamic rollover procedure of ECE-R66 test. While the paratransit fleet is outnumbered by the regular transit buses, and experimental testing of the buses seems to be prohibitively expensive to local manufacturers, the FE simulations provide viable insight into the bus strength.