Roads look very inviting, and in some cases may be your only option, but roads are very hazardous.
Traffic will be an issue. My plan was to look for a gap in the traffic, keep enough speed to round out and float very low over the cars so they'll see me and land in front of them -- with a little luck they won't be talking on a cell, texting, eating lunch or putting on makeup and hit your from behind.
IMO the biggest threat from roads is wires. Lots and lots of electrical and telephone lines co-located along roadways and crossing roadways. You won't see the wire until you hit it -- look for the poles. Try not to cross an interestion -- more likely to having wires crossing the road.
I've been lucky, in all my engine failures I've been over an airport -- although the 3 times on takeoff I was a bit low.