That depends a lot on the rider's speed as well as the terrain, weather. A 30-mile RT commute would be a piece of cake for a fit rider on a road bike on flat terrain. It would be very long for someone in not-so-great shape or riding in lots of wind or hilly terrain. I commuted 22 miles RT on a fairly hilly route for 4-1/2 years and it didn't seem long to me. This fall my commute increased to 30 miles RT and it still doesn't seem that long (about 1 hour each way), but I've been cycling for many years and try not to carry a lot of gear. On a windy day when my legs are tired from a long (60+ miles) weekend ride, that 30 miles feels pretty far though.