Take the first, "D-Speed I", manage to pass the looping, and then just before the tunnel,
there will be a "anti-boost".
I have the impression it is slowing down the car much too long, even across the next checkpoint.
It is hardly possible to reach the next bridge after the jump.
I assume the reverse boost simply takes as long as the boost in the right direction,
but it is too long to take back proper control of the car.
I tried braking, do nothing, etc. but nothing helps really, other than to wait that the effect disappears.
From TMUF, the checkpoint was resetting the effect of the "no-speed" block.
So it should also eliminate the effect of boost, especially of reverse boost, if possible

Other suggestions:
- make the boost only slow down the car while it is on the boost block, as I presume the engine can detect the direction of the car

- provide real unidirectional boosts and a real braking block with two grades (yellow and red) that have only effect in the correct direction of the car.