Idling: Shutting ’em down

May 10, 2012
Use of technologies to reduce idling is both smart and lawful

The best way to save fuel and the environment— and avoid costly fines for violating anti-idling laws—is to turn those engines off whenever possible. Shutting down engines is not only better for the environment and your fuel budget, it’s also the law in most states, and fines for non-compliance can be large—reaching $5,000 plus jail time in some locations. As demands to reduce heavy-duty truck idling increase, fleet executives and owner-operators continue to look for the best idle reduction technologies available.

According to the Environmental Protection Agency (EPA), a typical commercial truck can waste a half-gallon of diesel fuel per hour while idling. Unnecessary idling just two hours per day squanders at least $1,040 per year per truck, based on a diesel price of $4/gal. The payback for use of engine idle reduction technology in fuel savings alone can come in as few as six months, depending on the solution used.

EPA studies indicate long duration truck idling consumes more than 1 billion gals. of diesel fuel annually at considerable costs to the trucking industry as a whole. Truck idling also emits more than 11 million tons of carbon dioxide and more than 180,000 tons of nitrogen oxides annually, as well as fine particulate matter and other harmful air toxins.

With the growing number of regulatory and financial incentive initiatives aimed at curtailing commercial vehicle idling, the American Transportation Research Institute (ATRI), in partnership with the Dept. of Energy’s Clean Cities Program and the New York State Energy Research and Development Authority, conducted a national survey in 2006 to gather information on the use of idle reduction technologies among trucking fleets.

The most extensive study ever on the topic, survey participants provided data on more than 55,000 trucks, allowing researchers to compile a comprehensive profile of idling and the use of idle reduction technologies. The study found:

Sleeper cabs were reported to idle an average of 28 hours per week, which equates to 1,456 hours annually. Day cabs were reported to idle an average of 6 hours per week, which equates to 312 hours annually.

  • About 36% of respondents with sleeper cabs used onboard idle reduction technologies, which provide power for heaters, air conditioners, and/or in-cab appliances while eliminating main engine idling. These technologies were reported to be used an average of 29 hours per week or 1,508 hours annually.
  • The most prevalent onboard technology was directfired heaters, which were used by 32% of respondents with sleeper cabs.
  • Battery-powered air conditioners were used by 24% of respondents with sleeper cabs, while auxiliary power units/ generator sets were used by 12% of respondents with sleeper cabs.
  • Direct-fired heaters were reported to be the least expensive onboard technology to purchase and to maintain.
  • Battery-powered air conditioners were the next least expensive technology to purchase and maintain, followed by auxiliary power units/generator sets.

Based on the reported average capital cost for each type of equipment installed, the study found respondents had already spent nearly $8.8 million on idle reduction technologies.

Following is an overview of different idle reduction solutions on the market today.

Idle limiters One onboard technology many fleets are employing is idle limiters, which automatically shut the truck down after it has been idling a predetermined amount of time to cut unnecessary idling.

Idle limiters use one of three types of timer-activation systems:

  • RPM/engine speed-activated. The system detects when the vehicle is at idle, based on engine speed, and activates the timer.
  • Parking brake/park position-activated. The timer turns on when the driver places the vehicle in park or engages the parking brake.
  • GPS-activated. This system tracks movement based on the vehicle’s satellite position. If the system detects no movement, the timer is activated. Some systems are based on simple engine timers, while others offer monitoring capabilities to allow fleets to evaluate driver idling habits and take corrective measures or offer incentives for compliance with fleet idle reduction standards.

Passive monitoring systems capture idling data, downloadable at prescribed times, to track how drivers are complying with idle reduction policies. Active monitoring systems are tied to GPS and provide fleet managers with real-time alerts when automatic idle cutoff or other related “faults” occur. When purchasing an idle limiter system, fleets need to make sure the idle limiter can be programmed to comply with all applicable state and local anti-idling regulations in the areas where they operate. Some technologies will only allow trucks to shut down at a prescribed time, usually after 5 min. of idling, but some states and local laws only allow truck idling for 3 min., so care should be taken in those areas to be sure the idle timer can be set low enough.

Auxiliary power units Auxiliary power units are portable, vehicle-mounted systems that can provide power for climate control and electrical devices in trucks without idling. These systems are generally composed of a small internal combustion engine (usually diesel) equipped with a generator and heat-recovery system to provide electricity and heat. For air conditioning, an electrically powered air conditioning unit is normally installed in the sleeper, though some systems use the truck’s air conditioning system. The prime selling point of truck APUs are the fuel savings received from not idling, but other savings—and some costs—are a bit harder to calculate and determine. For instance, you save money in less maintenance and wear by not idling the main engine and its associated components; however, you will have to spend money on maintenance for the APU. And if you pick one of the “notoriously bad APUs, the maintenance costs, in addition to the headaches and time you have to spend dealing with it will make for a very poor investment,” according to TruckAuxiliaryPowerUnits. com, a website dedicated to providing motor carriers with unbiased analysis of truck APUs. With so many APUs on the market, coming in so many varieties with different options, it can be difficult to select the right APU. A driver who works exclusively in the hot, muggy South should probably select a different APU than a driver who works the East Coast of Canada. “Additionally, there are some systems, which are, frankly, poorly designed and should be avoided regardless of your needs,” warns.

“Most truck drivers at least know someone who had a bad experience with an APU—some systems are notorious for being underpowered, poorly made, or having frequent breakdowns.” started posting reviews of truck APUs in early 2010 as fuel prices started rising again and continues to upload new reviews as offerings change or new companies enter the market.

“We are an independent source of information about truck APUs,” the website states. “While we are supported by advertising … we are not directly paid by any manufacturer or distributor. We also ask for any feedback from users who have experience with specific systems. We want to compile a thorough overview of what is on the market and help you make the best decision for your truck or fleet.”

Automatic engine stop-start controls

Automatic engine stop-start controls can sense sleeper temperature and automatically turn the engine on when the sleeper is too warm or cold. Fuel savings using this technology are minimal in extreme temperatures. These controls also add to engine wear and may disturb the truck driver’s sleep.


Many systems incorporate an inverter/charger, which is a combination of an inverter, battery charger and transfer switch in one. The inverter portion converts DC power from an energy source into AC power to provide clean and quiet household AC power to allow operation of a variety of electronic devices. The battery charger processes incoming AC power into DC power and recharges batteries using a multi-stage process, which helps assure maximum battery life. Some models are also able to automate supplementary power production with automatic generator start and stop capabilities.

Storage air conditioners

Thermal storage and battery-electric air conditioners (storage cooling) derive energy to recharge the storage device from the truck’s engine during operation or from plugging in to shorepower. The engine uses a small quantity of extra diesel for recharging the air conditioner. The emissions from burning this fuel (which are controlled by the engine’s emissions control system) occur on the highway rather than at the truckstop or depot.

Coolant heaters

Coolant heaters use the truck’s regular heat-transfer system. The heater is mounted in the engine compartment, draws gasoline or diesel from the fuel tank to heat the vehicle’s coolant, and pumps the heated coolant through the engine, radiator, and heater box. Coolant heaters keep the engine warm, reducing the impact of cold starts.

Cab or bunk heaters

These diesel-fired heaters supply warm air to the cab or bunk. An engine block heater can also be included. Fuel use and emissions from diesel heaters are very low because they supply heat directly from a small combustion flame to a heat exchanger. Standard diesel fuel is used. Cab or bunk heaters can be coupled with air conditioners if the trucker’s service area includes both cold winters and hot summers.

About the Author

Deborah Whistler

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