Getting off the highway and catching a hot, acrid brake smell - even though you barely used the brakes - is a clue worth chasing. Here is why your brakes smell after highway driving.
A dragging brake makes heat at speed
You do little braking on the highway, so a brake smell there usually means a brake is dragging on its own - a stuck caliper or a parking brake not fully released heats that wheel continuously at speed; see sticking caliper and one brake running hot.
Find the hot corner
Pull over safely and carefully check each wheel for heat and smell - the dragging corner will be much hotter than the others; see why brakes get hot. A dragging brake also hurts fuel economy and can pull slightly.
New brakes can smell briefly
If you just had brakes done, a mild smell as new pads cure and bed in is normal for the first drives and fades; see new-brake break-in. A persistent smell from one wheel is not break-in - it is a drag.
What to do
Do not keep driving on a dragging brake - it can overheat and warp the rotor or boil fluid. Free or replace the caliper and check the parking brake; see brake fade. Fit quality pads and hardware.