When required to stop at a railway crossing, within how many metres of the nearest track should the driver stop the vehicle?

Answer: D — At least 5 metres in a restricted speed area and at least 15 m in a non-restricted speed area

A Option A is incorrect because in a restricted speed area, the required stopping distance is 5 metres, not at least 5 metres. B: Option B is incorrect because the required stopping distance is always at least 15 metres, not 15 metres in any area. C: Option C is incorrect because the required stopping distance in a non-restricted speed area is at least 20 metres, not exactly 20 metres. D: This option is the correct answer because it takes into account both the required stopping distance of 5 metres in a restricted speed area and at least 15 metres in a non-restricted speed area.