I don’t know what’s used in automotive taillights. I’d be a bit surprised if they used dimming at all. Incandescent bulb taillights don’t use dimming. If any dimming is done, it’s done by having two bulbs and only lighting 1 to get a dimmer light.
Most LED tail-lights I’ve seen use an array of LEDs, In that case, dividing the LEDs into two sets (so two interleaved arrays) and turning one or the other set off is a reasonable way to get dimming.
The only reason to use flickering in taillights would be for heat control. The reason you can’t dump amps of current across an LED is because it would overheat. For one gloriously brief moment it’ll be super-bright, then dark forever. But the light output of an LED is roughly proportional to the current through it: an LED will be twice as bright with 200mA and with 100mA of current – and generate twice the heat/use twice the power. If you run the LED at 200mA and 50% duty cycle, it’ll have the same average brightness/heat/power as the 100mA continuous duty. But the eye works better as a peak-detector than average detector, so the 200mA/50% duty cycle LED will appear brighter than the 100mA/continuous LED.
But if they do use flickering for that, there’s no reason to use a frequency as low as 85Hz.
One thing I have noticed with some LEDs, especially red LEDs in dim light, is that they tend (to me) to visibly trail the object they are on. I gather that’s because in dim light the rods act much faster than the cones. It’s freaky to see the power light on a moving hand-held radio look like it’s an inch or so behind the radio itself at twilight. Similarly, I find it a lot easier to see flicker of PWM-driven LEDs by rapidly moving the LED or my head, so the flashes get spread out on my retina.
So to me, it’s easier to see weird effects with red LEDs in dim conditions where the LEDs and I are moving relative to each other – like watching car taillights at night.