Singapore Has a System of Traffic Regulation Called Electronic Road

Singapore has a system of traffic regulation called Electronic Road Pricing, in which traffic congestion is reduced by charging motorists who drive into the city center during certain hours of the day. Charging for use of a road is:

A) a price ceiling that reduces the excess demand for road usage.
B) a price floor that eases the shortage caused by the natural limit to how much roads can be built in a certain geographic area.
C) a quantity restriction, as the system involves charging motorists only if they drive into the city center during "certain hours" of the day.
D) shifting from a third-party-payer-market to one in which individual consumers have to pay for their consumption of road usage, thus seeking to reduce excess demand.