Question of the Month:
What are the weight limits for heavy-duty vehicles on interstate highways? What weight limit exemptions exist for vehicles equipped with idle reduction technology?
Under federal law, no vehicle weighing more than 20,000 pounds (lbs) on one axle, 34,000 lbs on a tandem axle, or 80,000 lbs overall may access federal interstate highways (e.g., Interstate 70, which runs across the country from Maryland to Utah), regardless of where they get on the highway. States must enforce these requirements, or they may not be eligible for federal highway funding. However, the U.S. Department of Transportation (DOT) allows states to offer weight-limit exemptions for heavy-duty vehicles (HDVs) with on-board idle reduction technology.
Please note that states may set their own weight restrictions for roads that start and end within their boundaries, but we will focus on interstate highway requirements here.
Idle Reduction Technologies
Federal regulations allow states to adopt weight exemptions for auxiliary power units (APUs) or other qualified technologies that reduce fuel consumption and tailpipe emissions from engine idling. APUs are portable, vehicle-mounted systems that provide power for climate control and electrical devices without idling. For long-haul trucks, these systems typically have a small internal combustion engine (usually diesel) equipped with a generator to provide electricity and heat. Other on-board idle reduction technologies include automatic start-stop controls, energy recovery systems, fuel-operated heaters, coolant heaters, and battery-electric and thermal-storage air conditioners.
State Weight Exemptions
States may permit HDVs equipped with idle reduction technology to exceed the specified weight limit by up to 550 lbs to compensate for the additional weight of the equipment. Theallowance was previously 400 lbs, but the federal Moving Ahead for Progress in the 21st Century (MAP-21) legislation, enacted in 2012, increased it to 550 lbs. States must enact a law or institute an enforcement policy with their own exemptions to reflect this increased weight allowance. A map of APU weight exemptions by state is available on the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) State Recognition of the Auxiliary Power Weight Exemption to Gross Vehicle Weight website (http://energy.gov/eere/
|APU Weight Exemption||Authority||State Implementation|
|550 lbs||State Legislation||CO, CT, FL, MD, MN, MO, NH, TN, VA, WV*|
|400 lbs||State Enforcement Policy||AR, IA, ID, LA, MI, MS, MT, ND, NJ, NV, OH, SD, UT, VT, WY|
|State Legislation||AK, AL, AZ, DE, GA, IL, IN, KS, MA, ME, NE, NM, NY, OK, OR, PA, SC, TX, WA, WI|
|None||State Legislation||CA, DC, HI, KY, NC, RI|
* West Virginia Code 17C-13A-4 refers to the U.S. Code directly for the exact weight.
States must require HDV drivers to demonstrate eligibility for vehicle weight limit exemptions. For example, drivers may need to have paperwork on hand that verifies theweight of the idle reduction equipment and be able to demonstrate that it is functional. Requirements are different from state to state.
More information on these state weight limit exemptions is also available on the Alternative Fuels Data Center (AFDC) Laws and Incentives database (http://www.afdc.energy.gov/
Refer to the following for more information on idle reduction technologies and state vehicle weight limit exemptions for this equipment:
- EERE National Idling Reduction Network News (http://energy.gov/eere/
vehicles/vehicle-technologies- office-national-idling- reduction-network-news)
- AFDC’s Onboard Idle Reduction Equipment for Heavy-Duty Trucks page (http://www.afdc.energy.gov/
- Argonne National Laboratory’s Idle Reduction Tools and Outreach Materials (http://www.anl.gov/energy-
systems/project/idle- reduction-tools-and-outreach- materials).