Safety Assessment and Multi-Objective Optimization of a Paratransit Bus Structure

Paratransit buses are used in the U.S. as a complementary service for regularly scheduled routes and are usually designed to transport disabled passengers in their wheelchairs. Paratransit buses consist of custom passenger compartments mounted onto separate cutaway chassis--usually built by reputable manufacturer like Ford or GM-- by a secondary manufacturer called a “body builder”. The lack of dedicated national crashworthiness standards, along with different construction methods used by paratransit fleet manufacturers, can result in a wide variance of passenger compartment structural strength. To ensure adequate crashworthiness performance, in August 2007 the Florida Department of Transportation (FDOT) introduced a standard stipulating that newly acquired buses must be tested for rollover and side impact conditions. The rollover test is performed using a tilt table test according to UN-ECE Regulation 66. The side impact test involves the impact of a bus by a common SUV or pickup truck. In the current study, a detailed FE model of a paratransit bus was used to perform LS-DYNA® explicit simulations of both rollover and side impact testing procedures per FDOT standard. LSTC IIHS solid movable barrier was adapted for the side impact test. Based on the results, the safety level of the bus was assessed. Subsequently, the response of the bus structure in the two impact scenarios together with the total mass were used as three separate objectives in a trade-off optimization study within LS-OPT®. The Pareto solutions were identified and presented using the newly implemented Hyper-Radial Visualization method in LS-OPT. The simulation results show that the original bus design would pass the FDOT testing procedure. However, appropriate redistribution of the mass can noticeably increase its strength.