If you plan on interstate travel, it's probably a good idea to understand the many differences in state traffic laws. The Insurance Institute of Highway Safety is creating a series of color-coded US maps to point out the differences in state regs, beginning with motorcycle and bicycle helmet laws.
The motorcycle helmet law map shows which states mandate helmet usage, have a partial helmet law, or no helmet law. Bikers wanting to ride with the wind in their hair can head over to Illinois, Iowa, or New Hampshire. Be warned, though, that the IIHS has found that states repealing or weakening their helmet laws have seen an increase in motorcycle crash deaths.
The bicycle helmet law map shows the different laws governing helmet usage on bikes. Bicycle helmet legislation varies greatly between states. There are seven different types, ranging from mandatory helmets for bicyclists 11 and younger to no laws on the books whatsoever. In California and New Mexico, all riders under 18 must wear a helmet.