I just discovered something while playing #145 in the Solo Campaign. It's a multilap track, but at the end of each lap there are two reverse boosters, right after an engine killer. If you continue to hold the accelerator while going over the reverse boosters, they will effect your car as a reverse booster normally would and ultimately stop your car. However,
if you let go of the accelerator and truly coast over the reverse boosters, they have the opposite effect and actually boost your car.
This is in Lagoon of course. I haven't tested in other environments. Based on how this track is built, I'm guessing it's an intended behaviour, although it's not immediately obvious when driving the track. Trial and error revealed it to me. Just wanted to give others playing the campaign a heads up about it. Just let off gas while going over the reverse boosters and you'll easily make it to the next lap.
Now I'm curious if there's other reverse boosters after engine killers earlier in the campaign where I could improve my times by letting off gas.
I'll have to play through all the Lagoon tracks again to find out.