First off, your night vision is 'destroyed' by light coming back from the road etc from your own headlights. It takes minutes to develop, and even very low levels of light 'destroy' night vision.

DOT still does regulate all or most those things and many other elements about vehicle lights you probably never thought about (and I'll get back to headlights in a couple of paragraphs.)

Ever notice that most cars with "animated" turn signals have a portion that lights up immediately, or the entire signal lights up full brightness immediately and then fades, versus fading up or gradually lighting up a larger area? That's because of a DOT regulation that says X amount of area / brightness has to come on when the signal first lights up. This is why Audi's animated tail lights, for example, usually have two areas - one that is animated and 'grows'...and another that lights up fully. Ditto for Mazda's 'pulsing' turn signals.

Ever notice that a lot of "cute utes" and crossovers with hatches have either brake/turn signals in the bumper awkwardly very low, sometimes in addition to ones on the hatch? That's because DOT regulations require turn, brake, and marker lights be mounted in/on a non-moving part of the body. Got a friend with an Audi Q-series? have them step on the brake / use a turn signal, then open the hatch and do it again. Bam, those red lights way down in the bumper you never see light up...now light up in place of those on the hatch.

DOT has standards around placement of turn signals near other lights (DRLs and headlight beams.) That's why on many vehicles the DRLs go out when the turn signal comes on, or in fancier european/japanese cars, the DRL and turn signal are the same element and it switches from white to blinking yellow.

DOT also used to require that only two sets of lights on the front of the car be turned on at once. This is why some cars deactivate fog lights when the high beams are turned on, and some older cars don't turn on the lows and highs at the same time.

Fun fact: DOT used to require rear facing fog lights only be on one side. I'm not sure if the regulation still exists, but back in the mid to late 90's, european car manufacturers started ignoring the regulation, installing bulbs in both tail lamps, because they would be inundated with customers complaining to dealers that "one of my tail lights is out." Thus the whole damn point of a rear fog light - is it one very bright light, driver's side - which is different from two or three very bright lights (brake lights!) - was largely erased.

But...back to headlights. DOT regulations used to require sealed-beam headlights well past when the rest of the world had moved to 'aero' headlights with reflectors shaped to better distribute light across the road surface and limit light spillage where it would blind oncoming traffic or be wasted.

DOT regulations used to require a crazy amount of light spillage off to the sides because they predated reflective road sign technology. I'm not joking when I say that DOT headlight regulations up until some time in the 80's had not been updated in around forty years. Many EU and Asian cars had to be sold with US-only sealed beam headlights when ROW (Rest Of World) they were sold with aero headlights, because they had to meet inferior, outdated DOT standards. This raised costs for imported vehicles and allowed US manufacturers to save costs by not developing better headlights, and US manufacturers and their unions liked that because it was effectively a tariff on imported cars.

Why did the standards eventually get updated? Ford bet the company - billions in late 1970's early 1980s money on the Taurus (successfully. It saved the company.) Ford needed aero headlights to meet its aerodynamic drag goals (which were insanely good even by today's standards.) So, suddenly Ford wanted aero headlights to be legal. Bam. Aero headlights became legal. And suddenly ever ford was getting aero headlights. They were still garbage compared to what was sold in Europe; many car enthusiasts with 80's/90's era cars illegally imported and installed european headlights because the beam patterns were so much better.

Nothing happens to US vehicle regulations unless US auto manufacturers want it. We lag the rest of the world in almost every standard imaginable. We lag on passenger car features (it took until something like the mid 2000's for ABS to be required!)

For example, in the EU, trucks are required to have:

- ABS, stability control, and automatic emergency warning/braking systems (and I think side collision warning systems? not sure.)
- Full mirror coverage
- bumper features that keep them from riding up a passenger car they rear-end
- trailer rear end crash bars that keep cars rear ending trailers from going under the trailer and decapitating the occupants
- modern emissions controls
- electronic logbook systems

In the US? A 1970's peterbuilt that belches black smoke, has sealed beam headlights, flat side mirrors looking back, no ABS much less stability control/braking...is A-OK. Similarly, our rear collision safety standards for trailers are very watered down because of trucking industry lobbyists. Saves the trucking industry tens of billions, and costs the rest of society probably hundreds of billions if not trillions between injuries/deaths/property damage/lost productivity and health impacts from essentially unregulated emissions.

There are "coach builders" that focus on skirting emissions regulations - completely legally - via regulations that let an old, pre-emissions-control truck engine be installed into a brand new truck body.

I could go on and on about how asinine, outdated, and ineffective US motor vehicle safety and equipment regulations are. I could go on even further about how completely ineffective motor vehicle inspections are even in states that require them, because they're conducted by a private business with a vested interest in ignoring customers not meeting standards or purposefully violating them.