If you're reading the brake lights on the car directly in front of you as an indicator to slow down, you have already lost the plot.

A competent driver is actively driving a minimum of half a mile ahead of themselves with more than adequate distance between the vehicle directly in front of them to allow a response to changing road conditions.

The car doesn't suddenly decelerate unless the driver completely pulls their foot from the pedal. This sounds like a skill issue on both sides.