Is it okay to shift the gear lever from D to R or vice versa when the car is still moving, but very slowly? Or how about doing the same from D or R to P?

Automatic and direct shift transmissions allow selecting reverse from drive or vice-versa at very low speeds such as during parking manoeuvres.

But when doing so, make sure your right foot is off the accelerator. In fact, selecting R or D when the engine is revving, even if the vehicle is stationary, is damaging to the transmission. Shifting the transmission lever from D to R or even N to D thus requires the engine to be at or near idling speed.

Shifting to P is different. In P or Park mode, the transmission engages a lever into a toothed wheel. In P, a car cannot be pushed, nor will it roll down a slope.

Because of this mechanism, shifting to P when the car is still creeping - no matter how slowly - imposes stress on the toothed wheel and the lever.

For the same reason, it is best to engage the parking brake before shifting to P on a slope, no matter how gentle it is.

Most modern transmissions incorporate a safety control that prevents deliberate or inadvertent selection of P when the car is moving above a certain speed. But it is still best to shift to P only when the vehicle is at a complete standstill.

Shreejit Changaroth