From the Rural ITS Toolbox report: Subsection 7.7 Bike Safety Systems
A Bicycle in Tunnel Warning System was deployed at a tunnel on Highway 971 near Chelan, Washington by the Washington State DOT. Flashing beacons on a fixed message sign are activated when a cyclist presses a push-button, and deactivated after a preset time interval has passed. The fixed message sign reads, "PEDS/BICYCLES IN TUNNEL WHEN FLASHING." The shoulder area near the tunnel entrance was widened to allow cyclists to pull off the road safely and activate the tunnel warning system. The system cost $5,000 to build and install in 1979. The cost was kept low due to the existing power source at the tunnel entrance.
System cost: $5,000 (1979).