Many homes get a momentary vibration whenever a heavy vehicle contacts a manhole cover, while driving. This can cause damage to the house over time. This issue can be greatly reduced, or eliminated, by not building the manhole all the way up to the road. A flexible sleeve/insulator would rather connect the manhole tunnel to the opening. A reinforced iron support plate (about 5 feet wide) would be added to help support vehicle force (rather than the manhole itself). So the manhole vertical section could be lighter duty, also.