Relay (Relay Driving) Common practice in the less-than-truckload industry, in which one driver takes a truck for 8 to 10 hours, then turns the truck over to another driver, pony express style.

Reefer Refrigerated trailer with insulated walls and a self powered refrigeration unit. Most commonly used for transporting food.

Retarder Device used to assist brakes in slowing the vehicle. The most common type of retarder on over-the-road trucks manipulates the engine's valves to create engine drag. (This type is commonly referred to as "Jake Brake" because the predominant manufacturer is Jacobs Vehicle Equipment Co.) Other types of retarders include exhaust retarders, transmission-mounted hydraulic retarders and axle-mounted electromagnetic retarders.

RFG (Reformulated Gasoline) Gasoline blended with pollution reducing additives. Common in the Milwaukee metro area..

Rider Policy  A policy the company might have that allows someone, not employed by the company, to ride along with you. Typically limited to certain times of year (April to November) and limited to age of rider. The Policy might also stipulate the person must be an immediate family member only. 

Rolling Radius Tire dimension from center of the axle to the ground; measured with tire loaded to rated capacity. Used in calculating geared speed.


RPM (Revolutions Per Minute) Measure of the speed at which a shaft spins. Most often used to describe engine crankshaft speed. Indicated by a tachometer.