Like the U.S.,Belize's roads are given in miles, and gas is sold by the gallon. The gas stations were re-branded in 2012 in our country as Puma and Uno.
Unlike other countries in our region where shaking down a tourist in a rental car is a small industry, in Belize you will usually not be pulled over for phony traffic offenses, and if you are stopped at a checkpoint, which often happens, it is rare but not unheard that you will be asked for a bribe. The police will invariable ask for your driver's license and check your windshield to see the license sticker. This is more pre-text to strike up a conversation to determined if you are transporting drugs or doing something illegal.
Driving at night is not recommended by me because there are a few people on the roads still after dark going home on bicycles and some are walking, it is very hard to see them because the streets are not marked fully and its hard to see the potholes and topes- that is Spanish for sleeping policemen.
The vehicle I would recommend for you to drive in Belize are the large four wheel drive, such as an Isuzu Trooper, Toyota 4runner, Jeep Cherokee or Ford Explorer. The reason for that is that they offer a smoother ride on the roads and the large tanks helps so that you don't always have to stop to put in gas.
(Toyota 4x4 off-road in the Flowers Bank area of Belize District, Belize, pictured.)