SAFETY: Four feet is the law!

Just now I was asked by a bicyclist to remind motorists that, when they are passing a bicyclist, they must allow four feet between their vehicle and the bike. It's Pennsylvania law. It's also the safe and correct thing to do.
Four feet means 48 inches. Period. End of story. Even on winding, narrow Chester County roads with no shoulders, or if you're in a hurry to get somewhere and don't feel like crawling at 15 mph behind a bicyclist.
If you get the impression that Tilda takes this personally and is steaming mad at the moment, you would be correct.

Here's the language in the driver's manual:
SAFE PASSING IS THE LAW
1. Before passing, you must first decide whether you can maneuver around the bicyclist. Be sure to check for oncoming traffic. When passing, you must allow at least four (4) feet between your vehicle and a bicycle in order to pass safely. If necessary and if you can do it safely, you are permitted to cross the center double yellow line so you can maintain the four (4) feet of clearance between your vehicle and the bicycle.
2. Unless making a left turn, bicyclists traveling more slowly than passing vehicles must keep to the right side of the roadway and must travel in the same direction as the rest of traffic. However, this requirement is waived on roads with a single lane in each direction.
3. When there is only one travel lane, bicyclists may use any portion of the lane to avoid hazards on the roadway, including keeping a safe distance from stopped and parked cars.
4. Drivers cannot turn into the path of a bicyclist who is riding straight ahead on a roadway or shoulder.
5. You cannot force a bicyclist off the road. If you do this, you may face criminal charges.
6. Bicyclists are considered to be vehicle operators and are expected to obey all traffic laws; however, they may travel at less than the posted minimum speed and may not be cited for impeding traffic. Bicyclists may operate on a shoulder or berm, but are not required to do so.