State says trees are too unforgiving

Recently, The Herald has published letters from readers who suggest that we plant shrubs and trees in freeway medians to help prevent crossover collisions. Unfortunately, this approach would increase the risk for drivers and their passengers.

WSDOT and other transportation departments around the county typically use shrubs in medians to reduce glare from headlights, prevent erosion or enhance the scenery along a highway, but to not protect against crossover collisions. Most shrubs will simply give way to the force of a fast-moving vehicle.

When trees are struck by a fast-moving vehicle they act like large, rigid posts, usually resulting in serious injury or death when they are hit by a vehicle. When a vehicle strikes a tree, the entire force of the collision is focused at the relatively small area of the vehicle making contact with the tree, which crushes that section of the vehicle inward, sometimes causing the vehicle to wrap itself around the tree.

Instead, we carefully design our freeways and install systems to help keep drivers on the freeway, prevent crossover collisions and protect drivers who drive off of the freeway. While some barrier systems are more forgiving than others, all are designed to provide vehicles leaving the freeway with a smooth surface to strike. The wider surface helps to protect drivers by more evenly distributing and dissipating the force of the collision across the vehicle striking it. Additionally, our barriers can better withstand the force of a fast-moving vehicle.

Examples of the engineered and tested systems we utilize include guardrail, concrete barrier, cable median barrier and extra wide medians. While no system can protect every driver in every situation on our freeways, these engineered systems offer far more effective protection than trees and shrubs. Read more about different barrier systems on our Web site: www.wsdot.wa.gov/maintenance/barriers/default.htm.

Lorena E. Eng

Regional Administrator

Washington State Department of Transportation