All but the last few miles can be driven in a car, the last portion is a bit rougher by nothing in comparison to the other side. As it should be, this IS the Hole In the Rock Trail, the other side would be the Emmigrant Trail or San Jaun Mission Trail, etc, etc. It doesn't even get you with in a couple miles of the HITR while the west side parts you right near the top. Its worth doing, but if your in the area it can be done in a day with ease including hiking the actual cut.
Its in books, check out the Massey/Wilson series as I know its featured there among others.