And I forgot—if you coast downhill in neutral, you lose the braking effect provided by the engine. Of course, your fuel economy gets much better–but it is dangerous.
Crystalguy
Some owners manuals warn against being at a standstill with the tranny in drive for too long a time. Can’t remember how long or why, and I’m far too lazy to go out to my car to find out.
Peace,
mangeorge
Work like you don’t need the money…
Love like you’ve never been hurt…
Dance like nobody’s watching! …(Paraphrased)
Standard transmissions don’t have “Park” because with the engine stopped, it is sufficient simply to leave it in gear (which many – most? – drivers of standard shifts do).
John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams
Leaving your car stopped, but in gear for long periods of time is (probably) a bad idea simply because you have two systems (brakes and transmission) working against each other. It saves “wear and tear” on these systems to leave it in Neutral or Park.
Sweet Basil
ps The “hill holder” on standard transmission cars is a trade name registered to and invented by Studebaker.
I am now aware of laws that make ‘driving’ in Nuetral illegal. Thanks, Uncle! 
Regarding the “buffer” between Drive and Reverse to protect the transmission, every car I’ve ever seen has a lock built into it that prevents accidental shifts like that from happening. That’s why you have that little button that you need to depress on floor shifters to change the gears. The old “tree shifters” had a mechanism that required you to pull the shifter forward (or something like that) before changing gears. Maybe if you really kicked the shifter it might jump from Drive to Reverse, but you’d have to kick it pretty damn hard.
Well you can indeed kick it with a manual. Can use it to save your life, if necessary.
What dat?
What dat?
—Konrad
It be holes in the brake shoes that, combined with other devices, cause your brakes to “lock up” when when backward force is applied to the shoes. They release when you go forward. Usually. Never worked very good.
Peace,
mangeorge
Work like you don’t need the money…
Love like you’ve never been hurt…
Dance like nobody’s watching! …(Paraphrased)
A few things to add to this:
Highly unlikely, unless you’re driving a 1935 Crappenwagen. Even my 1988 Escrotch had an electronic ‘stop’ that made the car just not shift if you abruptly went from drive to reverse. I suspect most other cars of a more recent nature have this feature, too. Besides, on an automatic, you’d not be picking up the gears off the side of the road, you’d be patching a hole in the tranny. The trans fluid pressure would skyrocket and blow out a gasket or something before it would lock the gears.
Nope. They aren’t working against each other at all. The fluid pressure is not at a high enough level when idling to cause this. If your idle is screwed, it does become conceivable. But in a hydraulic automatic transmission, the ‘clutch’ doesn’t activate until the engine is moving at a certain speed. Same reason you can’t usually push start an automatic.
In my experience, this is usually just a small plastic or metal pin or divot in the shifter itself, not in the tranny. In fact, I’ve driven a few cars where it’s broken, and didn’t lock at all.
Also, most cars will go from R to N without pushing in the pin, and from 1 to 2 to D to OD to N without the pin. It makes for some nice manual shifting of an automatic. BTW, don’t manually shift an automatic unless you a)know what you are doing or b)have a car made for that, like a Tiptronic-equipped Porsche, most BMWs, Lexii, MBs, and most newer, nicer cars.
–Tim
We are the children of the Eighties. We are not the first “lost generation” nor today’s lost generation; in fact, we think we know just where we stand - or are discovering it as we speak.