APU Weight Exemption Guide
Auxiliary power units (APUs) can help limit fuel use by eliminating the need to run the engine on idle while parked, yet still allowing the driver to enjoy the vehicle's comfort systems during rest stops. However, APUs can cause a problem for truckers who regularly drive near the maximum weight limits, as these units weigh several hundred pounds. Starting in 2005, the government — on both the federal and state levels — tried to create laws that helped overcome this hurdle.
The Federal Government Exemption Created Confusion — and No Mandate
President George W. Bush signed the Energy Policy Act of 2005, which increased the maximum gross vehicle weight limit and axle weight limit by 400 pounds on vehicles that had qualified idle-reduction technology, such as APUs.
Unfortunately, this law created more confusion than benefits, especially at the outset. In November 2005, the Federal Highway Administration published a memo stating the federal exemption could not pre-empt state regulations on weight limits. The memo also claimed that the federal ruling did not serve to compel the states to adopt the APU exemption.
This led to several years of confusion as states had to decide, individually, how to handle/implement the exemption. It did not take long for states to start adopting the exemption, even though a federal mandate was nonexistent.
The Updated Federal Guidelines
In 2012, President Obama signed a new highway bill called MAP-21. This bill expanded the federal weight tolerance to 550 pounds. This caused many states to rethink their legislation and create new laws expanding the weight guidelines.
While these laws are constantly in flux, states continue to re-assess their decisions and decide whether or not to follow the federal guidelines. Truckers and fleet professionals need to know the various regulations in each state through which they travel in order to avoid hefty fines and citations.
Some states now have laws on the books that outline their exemptions. Others don’t have laws, but do have enforcement policies in place that allow for the extra weight — so drivers would not be cited. A few states still do not have an exemption on the books for APUs.
How does this legislation affect you? The accompanying table provides state-by-state information about the current regulations, per the U.S. Department of Energy. Keep in mind that state laws can change, so drivers and fleet professionals should always check weight allowances before traveling at max capacity.
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