Any place you can park you can unpark

In the discussion this week on getting a car out of a difficult space, I think Tom was on the right track. All you have to do is reverse each step in the parking process in the reverse order the steps were originally made. This includes the case of the car sliding sideways on ice (although if you’ve waited too long you may have to recreate the ice). You can even unpark a car that’s had its body bent getting into position; you just have to unbend it at the appropriate point. There was a three-dimensional example of this in one of Douglas Adams’s non-Hitchhiker books where a sofa had become stuck on a staircase with a turn in it. The hero had run computer simulations to figure out how to get it out, and the program reported that it could not be done (which was a major part of the joke).

Of course it’s possible to “unpark” the same way you parked. It’s just more difficult to do in reverse, because the steered wheels are now at the “back end” of the vehicle instead of at the “front end.” Anyone who’s tried to back up with a trailed hitched up knows how that works.

If we all drove cars that had the steered wheels at the back end, and fixed wheels at the front, it would be a lot easier to “back” the vehicles out of tight parking spots! But either way, the path of the vehicle is entirely “reversible” as long as the steered wheels are steered along the same path going “out” as they took going “in.”

Must be how the magician gets those rings apart.

Is this a trick question?! Yes, you should be able to. Even in a tight situation, it just takes a little more effort. The one thing you have to remember while you are backing up, is that front of the car will swing out. My driveway have a slight curve coming out of the garage.Going into the garage is a breeze, but when i back out, i have to go straight back and turn sharply after i clear the garage door.

You can certainly steer a vehicle into a situation in way that it can’t be removed. Whilenot an everyday situation, one way to do it would be parking downhill and/or up against an immovable object (like a tree or a curb)in which the driver completes the parking maneuver with a slow roll to the tire but, because you rolled the vehicle the final few feet into position, the driver requires a dry park steer maneuver to execute the desired extraction maneuver. Several things can work against the driver: (1) pushing against the immovabble object requires enormous steering effort — possibly more than the power steering can deliver (2) parking on a a severe downhill slope against the immovable object (so you can’t drive forward to escape) can shift enough vehicle weight forward that the power steering may not be able turn the statically-challenged tires. The callers’ scenario about the garage prorbbaly didn’t have a severe slope but there was some mention of a curb that could impose the undesirable tire restriction. Again, park while rolling may not be undone if the first maneuver attempted requires the wheels be turned while the vehicle is stationary (tires with good adhesion on dry clean surface).

...Anyone who's tried to back up with a trailed hitched up knows how that works...
If you think a trailer is difficult, try something like a farm grain wagon, hay rack, or anhydrous ammonia tank. Things like that with a tongue attached to steerable wheels on the front of the trailer are a real pain in the a** to back up! And it's pretty easy to pull it forward into a spot that you can't back it out of.

I believe you…but I’m pretty sure the question came from a guy who didn’t have an anhydrous ammonia trailer hitched to his car when he pulled into the garage :wink:

You touched on the critical factor: the front end of the car swings out.
Consider when you complete a (forward) turn, how the back of the car tracks into alignment with the front, even though the wheels stay parallel with the final direction of the turn.
This maneuver is not reversible, since there is no way to get the back of the car out of alignment with the wheels without turning the steering wheel. The front of the car has to move away from the direction of the turn before the back end will begin to swing around. If there isn’t enough clearance on the side of the car, the turn is impossible in reverse.

I believe you...but I'm pretty sure the question came from a guy who didn't have an anhydrous ammonia trailer hitched to his car when he pulled into the garage ;-)
Definitely, but you brought up trying to back up a trailer. I was just trying to point out that when you're pulling things like that, the more points where things turn or pivot, the more difficult it becomes to back up! It's not unusual to pull two ammonia tanks, or two grain wagons (which both have tongues and steerable front wheels on the running gear chassis), but you can't back them up reliably. I was just illustrating that just because you can go forward with something doesn't necessarily mean you can get it out in reverse.

There is at least one glaring exception to this rule; if you are towing two trailers. If, like a UPS truck, or a fifth wheel camper with a boat trailer attached to the fifth wheel trailer, you are pulling one trailer behind another, you can not, under any circumstances, back the rig up and make it go where you want it to go without unhooking one of the trailers.