About a third of the population of the U.S. lives in one of those states or cities. Enforcement is rare, and helmet acceptance is probably too low for compulsory laws to work well at present. There are more bright colors and more style choices. Some models with oversized vents are very cool but have less foam in contact with your head, which could concentrate crash forces. Some have easier strap adjustments and many have rear stabilizers to improve fit.
Many designs have sharper, squarer lines, departing from the rounder, smoother, safer shape.
There are helmets now for downhill mountain bike racing with face protection. The CPSC standard now is legally required for all helmets made for the US market after March, 1999. Helmets are cool, cheap and effective, and this is a good year to be buying one. It became BHSI in 1989, in hopes of setting up our own lab test facility. That did not happen, but the rest of the program did, and we are very active.