1. When you go to input an address, do not enter the house number or street and the GPS will pull up a list of streets. Select one and the GPS will route you there. It's not perfect since it likely will not get you to the center of a city, but it should get you reasonably close.
2. Go to the main menu while in the route and press the Detour button that appears next to the stop button. This will tell the GPS to generate a new route that should avoid the obstruction by going around the road.