#3 – Lighting and Advance Warning of Bicyclists in the Knapps Hill Tunnel

State of Washington

Greg Morehouse, WSDOT North Central Region


The Knapps Hill tunnel is located on U.S. 97A in the North Central region of Washington State. U.S. 97A is a scenic route that parallels the Columbia River north from Wenatchee through the resort city of Chelan on the south shore of Lake Chelan. This route offers views of wildlife including deer, bighorn sheep, eagles and an occasional moose, making it an attractive ride for the weekend biker and large bicycle groups. The Knapps Hill tunnel was originally constructed in 1936. The tunnel is approximately 214 m (700 ft) long on a 6 percent grade and, unfortunately, only 7.6 m (25 ft) wide. The steep grade and narrow width of the tunnel meant that slower moving bicycles would be in the driving lanes during their ride through the tunnel.





The tunnel had no illumination until 1957 when a contract was let to place fluorescent lights through the length of the tunnel. The original bicycle/pedestrian warning system may have been installed at the same time, but is thought to have been in place at least by 1967. The system consists of a push button at each portal that activates flashing beacons on a “PED OR BIKES IN TUNNEL” sign located in advance of each end of the tunnel. The flashing beacon operates for a period sufficient for the bicyclist to travel through the tunnel. The shoulder was widened to allow bicyclists to pull off the road safely to activate the push-button. The system has been modified since the original was installed but remains basically unchanged. In 1988, the illumination system was upgraded with 400-watt, high-pressure sodium luminaries. The upgrade also allows the internal tunnel lighting to adjust based on the ambient lighting conditions outside. This minimizes the blinding effects of driving into vastly different lighting conditions.

Evaluation and Results

No specific studies have been performed to evaluate these improvements, but adding flashing beacons for advanced warning and illumination systems are common components in our established safety standards.

Conclusions and Recommendations

This system is performing well for the current levels of bicycle and vehicular traffic, and there is no plan for an upgrade at this time. The tunnel structure itself is currently being retrofitted with a concrete liner that maintains the current width and stabilizes the rock behind the existing wooden structure. Any future upgrades for bicycle safety would more than likely involve moving the bicycle traffic to an alternate route.

Costs and Funding

Information obtained from: http://inform.enterprise.prog.org/p22.html

The flashing warning system cost $5,000 to build and install in 1979. These costs were relatively low as a power supply was already in place to provide lighting on the tunnel. Had this not been the case, installation costs would have been significantly higher.


Jennene Ring
WSDOT North Central Region Traffic Engineer
P.O. Box 98
Wenatchee, WA 98807
(509) 667-3080