Is police radar accurate when he is traveling toward you?

Yes. The radar calculating unit is reading more than one speed. It reads the patrol car speed from stationary objects (the ground, signs, etc.) and subtracts that speed from the speed at which your car and his car are coming together.

If the patrol car is doing 38 and you are doing 55, the radar unit will read 38 from the ground and 93 from your car. It subtracts the 38 from the 93 and displays your speed as 55.