Easy walk from the car, but look out for traffic and stay in the walking section of the bridge beyond the tire guides. You may want a flashlight to find the geocache ,it can be dim inside the bridge. Take care not to drop anything when accessing the cache, it may end up in the river below through the small gaps in the structure.
From the parking lot there is also a short but steep path to the swimming hole below the bridge if you want a different perspective. Very scenic, bring your camera.