A parked semi burns about 0.8 gallons of diesel an hour just to keep the cab cool or warm, and a long-haul truck idles about 1,800 hours a year during rest breaks alone. This page argues for storing cold while the truck drives, and plugging in where it parks, so the engine can sleep when the driver does.
The chain of the argument: a parked car or truck only makes cold air by running its engine → drivers who must rest or wait in the heat idle for hours → that burns fuel, wears the engine and is limited by law in places like California → the truck’s own air conditioning could freeze a cold store on the road, and a plug at the parking spot could run the cab off the grid → so build cabs that bank cold while driving, wire the spots trucks already park in, and show the gallons saved.
This is a concept, not a product. The idling figures, the truck parking count and the plug-in prices come from the US Department of Energy, the Federal Highway Administration and a 2015 DOE-funded study, linked at the bottom. The prices are from 2015 and today’s differ. The ice math is physics with an assumed cooling load; a real cab’s load depends on sun, color and insulation.
No engineering knowledge needed. Read this part and you’ll understand the entire page.
It started with a private investigator. On r/AskEngineers, someone who does surveillance from a parked car asked how to stay cool without running the engine, because an idling car gets noticed and a closed one bakes. The thread ran to hundreds of answers: run the air conditioning off a big battery, or use the kind of ice-and-fan cooler some pilots carry.
Truck drivers have the same problem every night. Federal rules make long-haul drivers stop and rest, often in a sleeper bunk behind the seats. To keep that bunk cool in summer or warm in winter, many leave the engine running. The Department of Energy says an idling heavy truck burns about 0.8 gallons of diesel an hour, and a long-haul truck idles about 1,800 hours a year during rest breaks.
Idling is wasteful, and in places it’s illegal. California limits most diesel trucks to five minutes of idling. Fixes exist, from battery-powered air conditioners to plug-in hookups at a few truck stops, but most cabs still make cold the old way.
Here’s the redesign. While the truck drives, its own air conditioning also freezes a cold store under the bunk. When it parks, a small fan pulls cold from that store with the engine off. And where trucks park overnight, a plug post runs the cab’s air conditioning or heat from the grid and tops the store back up.
About 0.8 gallons an hour for a heavy truck, per the US Department of Energy. Checked November 2026.
Sources: DOE Alternative Fuels Data Center, heavy-duty idling (2015) · AFDC idle reduction research · the 2015 truck stop plug-in study (OSTI)
A truck’s engine is built to haul 80,000 pounds up a grade. Using it to run a cab air conditioner overnight is like heating a cup of coffee with a furnace. The engine burns fuel at idle, wears faster, and fills the parking lot with exhaust next to other sleeping drivers.
The fixes are known. Auxiliary power units, battery air conditioners, and truck stop electrification, where a post at the parking spot supplies power or even conditioned air through a hose, have all been sold for years. The 2015 study found plugging in cost less than half of idling. What’s missing is the default: new cabs that come ready to sit quietly, and parking spots that come with a plug.
Parking is the other half of the problem. The Federal Highway Administration counted about 313,000 truck parking spaces in 2019, most at private truck stops, and truck stops reported being over capacity overnight. Any plug has to go where trucks can actually park.
Cold is heavy and bulky. N‑3 shows a hot night could take over 100 kilograms of ice. Phase-change packs and better insulation help, but space under a bunk is limited, and weight counts against cargo.
The A/C can’t always do both. On the hottest afternoons a truck’s air conditioner may barely keep the cab cool, with nothing left over to freeze a store. Patents on these systems call this out.
Plugs need parking. Truck stops already run over capacity at night. A plug on a spot a driver can’t get to doesn’t help, and the truck needs its own gear to use it, estimated at about $4,000 a truck.
Battery air conditioning already works. Battery-powered systems sold for sleeper cabs can cool through the night, and electric cars can run their air conditioning parked from the main battery. For the private investigator in the car, that may be the simplest answer.
The prices are old. The plug-in costs are from 2015. Diesel, power and hookup prices have all moved since.
The whole idea, in one line
An 80,000-pound truck’s engine shouldn’t run all night to cool one bunk. Bank the cold on the road, and plug in at the spot.