Well in Europe anyway there is by far a big enough difference in brightness between the tail lights and brake lights that you definitely notice when the brake lights are on. There is a very good set of standards that eveything is built too. Also, most new cars are fitted with a third brake light in the centre to remove any confusion.

(list 6284, Mk1 S/N 00299 4GB blue [for sale]. Mk2 S/N 080000094 6GB blue)
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(list 6284, Mk1 S/N 00299 4GB blue [sold]. Mk2 S/N 080000094 20GB blue)