On the Federal Interstate Highway System, long-haul trucks are generally limited to a gross vehicle weight (GVW) of 80,000 lbs. That limit includes the weight of the truck and trailer as well as the truck’s cargo and fuel. Obviously, drivers hauling boxes of potato chips have less of a problem with weight limits than haulers of lead-acid batteries.
When the trucking industry began to realize the value of using APUs to save fuel during rest periods, drivers hauling heavy cargo were at a disadvantage. Although APUs offer considerable benefits, they are heavy and that weight counts towards the 80,000-lb limit.
Fortunately, in 2005, Congress passed the Energy Policy Act, which revised these standards, along with a wide range of energy issues. To promote the use of idle reduction technologies that reduce fuel use and emissions, Section 756 of EPAct allowed states to permit a 400-lb exemption for vehicles with APUs without risk of federal funding sanctions.
The 400-lb ceiling covered most APUs available in 2005. However, battery-based APUs soon came to the market, many of which weigh more than 400 lbs. In 2012, Congress enacted Moving Ahead for Progress in the 21st Century (MAP-21), which in Sec. 1510 further increased the APU weight allowance to 550 lbs.
The map below shows the current status for the APU weight exemption across the country. (An interactive version is available on the Vehicle Technologies Office's idle reduction webpage.) As you can see, a number of states have adopted the 550-lb exemption, but most have not. To complicate matters, there are states that permit a weight exemption not by law but instead by enforcement policy. A few states, including California, permit no APU weight exemption.
