Can a cop detect your speed while behind you while he's coming from an angle?

Question

I was just stoped and given a ticket while driving on the freeway.

The cop said i was speeding and going over the limit. Then i asked him how much was i over the limit and he didnt give me a stable answer ( he said, like 70 o 75 ) and the ticket was for 78 !. then when i asked him were was he at when he detected me and he said he was coming up the ramp to get into the freeway.

The weird thing is that their radar can detect speed while both vehicles where in movement, yet i was going straight and he was coming form an angle towards me. (coming up the ramp) which means that he wasnt straight behind me or in front.

CAN THAT RADAR DETECTION BE ACCURATE?

BECAUSE I KNOW I WAS GOING AT 65 on cruise control !

but while i asked the questions he started giving me attitude because i told him i was just asking cause i was going to court to fight for it. ( he got mad like if he knew i knew he didnt really catch me on the radar)

Answer 1

Yes the detector can read your speed from the side, from the front, from the back and from the top.

Answer 2

You are correct on one thing... in order for radar to be accurate, you must be traveling directly towards, or away from, the radar unit. However, if you are clocked at an angle, the error is always in your favor. The technical name for this is a cosine error.

He could have been using VASCAR (Visual Average Speed Computer And Recorder). This is a system that times you between two known points. This is why you can occasionally see white lines painted on the road. The lines are a known distance apart, so he just times you between the points. Speed is equal to distance divided by time, so it is a simple math calculation.

He could also have clocked you on radar from an overpass, long before you saw him on the ramp.

Answer 3

The simple answer is yes.  There are Radar's that are able to read traffic going in the same direction either in front of or behind the unit.  Unfortunately for your court case, the angle of approach actually gives you the benefit of the doubt.  The more straight on the more accurate the reading.  The steeper the angle the LOWER your speed will read to the unit.  This is called the cosine angle effect.  

This is assuming the Radar unit was set up properly and was properly used by the officer.  It also assumes the reading the officer observed was from your vehicle and not another one nearby.  

Another thing about speeding tickets and Radar.  I do not need a Radar to write a speeding ticket.  My observation is what gets the job done.  The Radar only a tool I use to confirm my observation.