I've never contested anything, but maybe take a picture of that intersection and take that with you to court
Only one I've ever had that I thought of contesting was some cop that was bored, and tailing me .... and I thought I was doing everything right. Following the signs, etc. Sped up towards the posted speed as I was leaving residential, with him still tailing me. Bah ... I wasn't past the sign yet so he got me for like 2 or 3 over residential. But it would have been a 3 hour drive to contest it.