Also APU weight exemption in some states http://energy.gov/eere/vehicles/map-state-recognition-auxiliary-power-weight-exemption
When I was driving a international pro star pretty much every load I was 12300 on steers. Never had a problem at any scale.
single axle group is allowed 20k or the lowest rated component of the axle assembly ie tires/axle itself.
http://www.ecfr.gov/cgi-bin/text-id...rgn=div5;view=text;node=23:1.0.1.7.33;idno=23 The exceptions (Interstates which are not on the national network): i580 in Oakland, i66 in D.C., through truck traffic on interstates inside the Atlanta beltway, i895 in Baltimore, i93 in Boston, and i264 in Norfolk.