Date of this Version
Julin, R.D., Identification of a Maximum Guardrail Height for the Midwest Guardrail System Using Computer Simulation. MS Thesis. University of Nebraska - Lincoln, NE. 2012.
W-beam guardrails are by far the most common restraint system used along both local and major roadways. Traditionally, these restraint systems have been full-scale crash tested with a rail height ranging between 27 in. and 32 in. However, the maximum rail height which allows for safe performance of guardrails, especially in impacts involving small vehicles, has never been identified.
The main concern associated with an increase of the rail height is that small vehicles, because of their low profile, may have a tendency to lift the rail and penetrate the barrier. The objective of this project was to determine the critical rail height at which small vehicles start under-riding the barrier. A potential increase of the rail location could provide several benefits in terms of an improved safety of the system with vehicles characterized by a high center of mass, economic advantages related to the maintenance of the roadside, and accommodation of potential frost-heave and erosion.
This study used computer simulations to investigate the safety of the Midwest Guardrail System (MGS) with the rail located higher than 32 in. from the ground level, considering various impact angles and grading scenarios ranging from flat terrain to minor slopes. Also, the potential problems and the influences of different frontal geometry of vehicles were considered.
With consideration given to current small car design trends, this study showed that on level terrain the MGS would satisfy MASH TL-3 evaluation criteria with rail heights up to 36 in. Furthermore, it was shown that successful containment of errant cars and trucks may be achieved on 6:1 approach slopes when the rail is mounted at 36 in., and improved pickup truck redirection was shown on 8:1 approach slopes with increased rail mounting height.
Full-scale vehicle crash tests are necessary to confirm these simulation results before these taller systems can be deemed crashworthy according to MASH and implemented.
Advisor: John D. Reid