Prolonged Rocket Boost (sometimes referred to as Permanent Rocket Boost), or PRB, is an advanced technique/glitch in Mario Kart DS that allows players to maintain top speed even while driving over stretches of Off-Road. It is an extension of snaking, and requires a high-level of snaking mastery to perform.
Players maintain PRB by performing consecutive Mini-Turbos within an extremely strict window after a Rocket Start or Boost Pad boost; they must perform their next mini-turbo before the previous boost wears off. This tricks the game into believing that the boosts from the mini-turbos have the same properties as the initial start or pad boost, essentially allowing players to extend that boost for as long as they can maintain the mini-turbo chains, and cut through off-road at full speed well into the course.
The very same karts that are ideal for snaking (the Dry Bomber, Egg 1, Poltergust 4000, ROB-BLS, and the Standard Karts of Luigi, Yoshi, Dry Bones and R.O.B.) are also among the only karts that can perform PRB. Longer mini-turbos allow more leniency with maintaining PRB; as such, out of the aforementioned karts, the Dry Bomber is the easiest to learn the technique with, and the ROB-BLS is by far the hardest (albeit the most rewarding). The only other karts capable of PRB are the Mushmellow and the Shooting Star, which are never used in top-level Time Trials; their high drift makes it difficult to maintain good racing lines, and they are entirely outclassed by at least one of the ideal snaking karts otherwise.
PRB is extremely difficult to learn, and even the best Time Trial players in the world can struggle maintaining it on courses with elevation changes or gaps, such as Peach Gardens or Sky Garden. Because of the skill gap it creates at the high level, world record tracking websites such as the MKDS Players' Page often split Time Trial records into PRB and non-PRB categories, with the latter specifying where in the course a player must stop using PRB.