We have a mt. tunnel on one of our weekly rides. It is short, but it is dark and narrow... and the traffic is moving along a pretty brisk pace. Occasionally a truck driver will have the foresight to see what's happening, and will slow down enough to essentially run blocker for us. Passenger car drivers almost never get this and will try to squeeze by, no matter how narrow, even though it would only cost them about 3 seconds to wait for us to exit the other side.