Booster Track

A short row at the start of a line does the whole job. Three back to back push a standard minecart to its ceiling, faster carts want a couple more, and past that point you are wasting money because the cart cannot exceed its own top speed.

Put them where you launch and after anything that slows you down, like a climb or a station stop. Long flat stretches do not need them repeated.

Each one points a way, shown by the arrow on its face, and hitting it from the wrong side brakes you instead of speeding you up. On a two-way line that means a booster helping your outbound trip fights your return trip, and enough of them will stop you dead or send you backward. Either run separate tracks for each direction or wire them so you can flip them on the way through.

You can only change the arrow when the piece is connected to track on both sides, which is worth checking before you decide a booster is broken.