In many developed world, human cost is the most expensive items in any business. In the world of parking, at what point it is cost effective to hire parking attendant?

In Japan, many of the open air parking were turned into machine controlled lots. When you park your car at any spot and a flat that urns up making car locked in. The only way you can unlock and free the car is to pay the due.

Also, parking lots are monitored 24 hours. If you park the car without activating the flap, a flap can be turned on after xxx minutes. Many of the US parking are controlled at the gate with usually people looking around.

I think the parking system like this wil work in the US.