Compliant Norm says the most important priority of the Department of Transportation is to promote the economy. Nothing boosts the economy like running big trucks through residential neighborhoods. Just think of the benefit to the building material, health care, pharmaceutical, chemical, petroleum, tire, hospital, mortuary, auto repair, auto manufacturing, junkyard salvage, construction, real estate, title insurance, and demolition industries. People have to buy acoustical tile to line their houses just to hear each other talk. Even then, they need prescription sedatives to cope with the noise.
Houses have to be painted often to cover the diesel soot.
Children cannot cross the street safely, so parents have to drive them around, consuming gasoline, tires, etc. If someone is run over, expensive surgery may be necessary, perhaps followed by a funeral. The streets will crack, causing wear and tear on car suspensions. Cars may have to be junked earlier. Eventually, those with the means will move out, requiring new construction, real estate transactions, title insurance, etc.