Ok, your talking in the right of way ...I did the underground trench utility designs for 9 years. Gas and electric were 24". Telephone and CATV were 18". These were for new construction. Add on construction could be anywhere. All of the utilities went from their terminal points to a common utility point on the house. They were in a single trench.
Sometimes…. electric and CATV are in conduit so replacement is pretty easy. Telephone, specifically Pacific Telephone, Pacific Bell, SBC, ATT are direct buried and use encap termination directly onto the feed cable. That is always a sidewalk digup.
I thought you were talking about from the ped to the houses.
Fortunately you don't usually get Cable cuts Under a sidewalk, usually its when a Construction crew us digging with major equipment.
The drops to the house are not going to be very deep, sometimes barely under the sod. 6" is a godsend.