Measuring Vehicle Speed

My son was stopped and given 55km/h in a 40km/h ticket. He is 20 so I am afraid of his insurance go up.

The cop was driving from in the opposite direction and my son was driving last behind 2-3 cars. My question is, how could the cop prove that he caught my sons car speed on the radar in this situation? I read his notes are talking about estimated speed 65/40 460m, 66/40 410m. The typed notes are not consistent with hand written either (no speed mentioned). Any idea for defence tactics?

Also it is a 40km/h area, which as I know requires a bylaw. The bylaw was nor included in the disclosure package. Could we play that card as well?

Any ideas appreciated.

Thanks,

Slepy.