Did the 34 mile loop on April 11, 2015. Perfect weather. Started at the parking lot near the trailhead to the RR tunnels. Went clockwise heading up toward Boulder City. Although tempted to ride the highway for the first few miles, we decided to ride it as it was laid out. After being directed through a concrete drainage channel for a couple miles we ended back on the asphalt trail about 5 miles into the ride. The trail is well marked so there is no worry about getting off course. There are a few rr crossings for a 4 car tourist train which blew the horn at us. There are a few spots to replenish your water or get a snack. The ride is moderate with breath taking views and the trail is in good shape. I highly recommend starting where we did (mile 24.5) and doing the climb toward boulder city first, that way you can get the tough part out of the way while you still have your strength. This trail is a must do for any recreational cyclist with a few hours to kill. We took it very easy and finished in just over 3 hours. I'm sure you could do it in less than 2.5 hrs. It was a blast and as a native, a great way to appreciate the area.