Federal bridge formula axle groups. Axles 1, 2, and 3 are the tractor group. Axles 2, 3, 4, and 5 are the trailer group.
U.S. Department of Transportation/Federal Highway Administration
2008-02-03
<a rel="nofollow" class="external free" href="http://ops.fhwa.dot.gov/freight/sw/brdgcalc/calc_page.htm">http://ops.fhwa.dot.gov/freight/sw/brdgcalc/calc_page.htm</a>