The problem is also that generally, engineering takes what is best practice for an interstate with speeds in excess of 55 MPH, and then apply it to local roads

The problem is also that generally, engineering takes what is best practice for an interstate with speeds in excess of 55 MPH, and then apply it to local roads with driveways where people are trying to cross the street. Even a street dead ending in a cul-de-sac and no legal steeet parking is often in excess of 30 feet wide. All that width encourages speeding.