As long as the engine is running and the driver door remains closed or the driver's seat belt is fastened, it will remain in neutral. I think the brake pedal state is also included in this logic.

If moving above a few miles an hour, you can shift between neutral and drive or reverse without stepping on the brake.

I seem to recall a method to leave the transmission in neutral with the engine off but can't remember where or why it was done.

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8/2011 X5 xDrive35d Sport, Black Sapphire Metallic, Black Nevada Leather, Fine Burr Walnut Trim
2/2001 M5, Jet Black, Exclusive Complete Black Walk Nappa Point Heritage Leather, Black Cubic Trim