[GreyCoupe]

I think is a vestigial National Highway Safety requirement. Back in the day, cars were not being designed so that side reflection/lighting was sufficient for safety, in their opinion.

This requirement was designed to solve that. That the rest of the world, and now US cars are designed with ample reflective surfaces, they have not responded by ending this requirement. There may have been similar European requirements as for years lights were stuck on the sides of some cars that looked like complete afterthoughts. Some, like BMW, now even include integrated lighted side markers, but still these ugly reflectors are required in addition to lighted side markers in the US. Doh!

Maybe the government has stockpiled these by the millions, so we cannot now end their requirement, as it would trigger more unemployment.

The interruption of the lines of hot cars has been so annoying as to create a US aftermarket of replacement panels designed to be painted to hide! Bureaucracy dies hard in America, so automakers still have to mount them to import/or manufacture cars here. Instead of merely ending such US requirements, we usually replace them with even less needed, more stringent rules, so no one is saying anything about them.

Permanently lighted running lights, or even lighting headlights would accomplish the same results, but don't forget, we have tons of reflectors stored in strategically located warehouses around the country!