Pat yourself on the back for having such a good feel for reality. I suppose you have an advantage over most folks since you are actually out there riding and walking. It looks like trucks, motorcycles and buses account for a bit less than 40% of the vehicles on the road. Of course, if we were to exclude the restricted-access roads and only look at the places cyclists and pedestrians are moving, it's going to be much lower. (Nope, I can't find any estimates, but in my experience as a commercial truck driver tells me that a good 80% of truck miles are on restricted access roads, at least out here in the Western US.)

See p 15. http://www.epa.gov/otaq/models/moves/420r10026.pdf