EFFECTS OF PRESENCE OF LIGHT POLES ON VEHICLE IMPACT OF ROADSIDE BARRIERS. FINAL REPORT

When light poles are installed within the deflection zone of guardrails, they may influence the ability of the guardrail to safely redirect an impacting vehicle. Although most highway light poles are designed to "break away upon impact", insufficient data exist to verify that as a vehicle deflects a guardrail into a light pole, the light pole effectively breaks away. A concern is that light poles may act in a manner similar to bridge abutments. There is evidence that in crash situations where the vehicle pushes the guardrail into the abutment, it generally pivots about the relatively rigid abutment and is injected back into the traffic stream in an uncontrolled, unsafe manner (e.g., spinning). While the size, mass, and stiffness properties of a light pole are much different from a bridge abutment, they may be sufficient to degrade the redirecting performance of the guardrail. If light poles have an adverse effect on the performance of guardrails, then significant and costly modifications and replacements may need to be made to existing barriers and light poles. Required actions could include moving existing light poles out of the deflection zone of the guardrails, stiffening the guardrails to reduce their maximum deflections (which in turn could degrade their redirecting performance), retrofitting existing light poles with new, more frangible bases, and replacing entire light pole assemblies. Full-scale testing involving 2000P and 820C type vehicles were performed and limited computer modeling runs were made to shed light on these concerns and assess if and how existing light pole designs affect the redirecting performance of guardrails under impact conditions. The results from testing and modeling activities indicated that in no case did the vehicle (either 2000P or 820C) snag the guardrail/light pole system more seriously than the case when no light pole is present. Based on these results, no change in the current configuration of light pole installation is recommended.