When one is driving downhill with a car in gear, one is maintaining speed, not slowing down. Hence there is no need to show a brake light.
Driving down a long hill using (friction) brakes to maintain your speed is a quick way to cause excessive wear on your brakes and, in extreme cases, lead to overheating and brake fade or failure.
This is required knowledge for the UK driving test BTW.
Sorry - I should clarify I downshift. I understand the difference. I drove manual most of my life. (Somewhat unusual in the USA )
However, I frequently see drivers fly down the mountain behind me, and then brake heavily. The drivers in front of me, have their brake lights on in front of me usually the entire time or nearly.
However: high compression engines will slow you at a rate similar to light braking in many circumstances, unless your gearing and the slope of the hill is just right.
On my motorcycle, if I’ve downshifted to an amount that it will stop acceleration due to the slope, it will begin to decelerate me.
Even in my current car, the difference between 3rd and 4th is 4th allowing the car to continue to accelerate to ~20 mph over the speed limit, where 3rd will hold briefly but begin to decelerate the vehicle as the slope decreases.
While I can shift between them to moderate the speed, it’s not always worthwhile. Again, I’m applying specific scenarios where the “mountain” road is maybe 1-1.5 miles maximum.
The specific scenario I dislike is that if I’m using engine braking(say to maintain 35-43 mph in a 35 zone), and don’t tap my brake lights - people fly down doing 60, and the brake heavily, tailgate for a period, and then follow at a normal distance.
If I tap my brakes to trigger the lights as they approach, they begin to slow further away and don’t do the hard slowdown.
Anecdotal of course.
The difference may be that where I am in the USA many people are not using engine braking.
When one is driving downhill with a car in gear, one is maintaining speed, not slowing down. Hence there is no need to show a brake light.
Driving down a long hill using (friction) brakes to maintain your speed is a quick way to cause excessive wear on your brakes and, in extreme cases, lead to overheating and brake fade or failure.
This is required knowledge for the UK driving test BTW.