Refrigerated road transport moves chilled and frozen freight by truck, using a diesel or electric refrigeration unit mounted on the front of a trailer or box body to hold the air inside at a set temperature. Two vehicle types cover almost all of it: the reefer trailer, a semi-trailer pulled by a tractor unit and built for line haul between distribution centers, and the rigid reefer truck, a smaller box mounted on its own chassis and built for multi drop delivery runs into stores and foodservice sites. Both carry the same core equipment: an insulated box, a refrigeration unit at the front bulkhead, and a fan system pushing conditioned air the length of the load.
It is the workhorse of chilled and frozen food distribution, moving pallets between processors, distribution centers and stores at a cost per pallet far below air freight and a speed no ship can match over a few hundred miles. Nothing else moves a full truckload of chilled product between two inland points faster or cheaper.
Trailers, rigids and multi temperature compartments
A standard reefer trailer runs 40 to 53 feet long and holds a single temperature zone end to end, set for one product: frozen at around -18°C, or chilled at 2-8°C. A multi temperature trailer adds a moveable bulkhead partition, splitting the box into two or three zones running different set points on the same run, so one delivery vehicle can carry frozen, chilled and ambient product to the same store in a single trip. Multi temperature compartments cost more to build and run than a single zone box, so they earn their place on multi drop retail routes, where splitting the load across separate single temperature vehicles would cost far more than the extra equipment.
Set point against actual product temperature
The refrigeration unit controls one thing directly: the temperature of the air it blows into the box, called the set point. What the product itself sits at, its core temperature, is a different number, and the two only match once the load has had time to equalize with the air around it. A return air sensor near the back doors reports what air is coming back through the unit, useful for spotting a problem but still not the same reading as a probe pushed into the product itself. Shippers who need proof of product temperature, not just air temperature, fit their own logger into the load.
Pulldown against holding
A reefer unit is sized to hold a load that is already at temperature, fighting only the heat that leaks in through the walls and doors. It is not sized to pull a warm load down to temperature quickly. Loading product straight from a warm dock into a reefer trailer and expecting the unit to chill it in transit is one of the most common and most avoidable causes of a failed delivery. The correct discipline is to pre-cool the trailer empty before loading, load only product already at its target temperature, and treat the reefer unit as equipment that holds cold, not equipment that makes it.
Door openings, standby power and telematics
Every stop on a multi drop run opens the back doors to warm ambient air, and the refrigeration unit has to work to pull the box back down to set point before the next stop. A route with twenty delivery points loses far more total cold air than a single line haul run covering the same distance without a stop. Loading the trailer in reverse delivery order, so the last stop's pallets sit closest to the doors and the first stop's pallets stay furthest from them, and hanging a plastic strip curtain across the doorway, both limit how much cold air escapes and how much warm air gets in at each stop.
Running the engine just to power the unit while a truck sits at a dock burns fuel the site may not allow; electric standby lets the unit plug into mains power at a depot and run without the engine turning over. Telematics systems report set point, return air temperature, door openings and fuel level back to a fleet office in real time, and raise an alert the moment a reading drifts out of range, turning what used to be a paper chart read after the fact into a problem a dispatcher can act on while the truck is still on the road.
The range it covers, and where it stops
Refrigerated road transport fits regional and continental lanes measured in hours to a couple of days, feeding stores, foodservice and distribution centers from a local or national network of cold stores. Past a certain distance, crossing an ocean, the lane shifts to a shipping container instead, with a truck handling only the first and last mile. For the smallest shipments, a handful of pallets or a single parcel moving to one clinic or one lab, a full reefer trailer is the wrong tool entirely: an insulated shipper or an active packaging container held on a standard pallet moves the same product for a fraction of the cost of dedicating a whole vehicle to it.