trip planning for urban driving
 

Dealing with places like Chicago, NYC, Atlanta, etc. is one of the things that intimidates me about becoming a driver. I'm pretty good at directions and following maps, but there are too many "surprises" in the cities -- the crazy drivers, everything too narrow and cramped, and probably many other things that I cannot even imagine yet.

Anyway, a couple of questions:

With the mapping software now available, do you still find city maps useful?

When I was nosing around a truck stop store, I saw a Chicago low clearances map. From what I've seen of the place, I would imagine such a map would be invaluable. Are there other specialized maps for one city or another that you find useful?

As a 4-wheel driver, I have many times found the street I had planned to take torn up by construction or blocked by an accident, and have needed to re-route myself "on the fly." That is easy enough in an automobile, but I sure don't want to try it in a truck. When you are planning your trip, do you work out an alternate route or two "just in case?"

It always seems to take me longer to get from A to B than I was expecting. Do you have any rule of thumb as to miles per hour in urban driving for when you are trip planning, beyond taking into account time of day, and places that you know will always be a headache and a likely delay?