It seems to me to be a significant error on the ticket if the officer did not know the speed limit of the road he pulled you over on. I think you could potentially create some reasonable doubt if you challenged the ticket, but you would have to be very well prepared to do that. My argument would be if the officer was confused about what the legal limit was, perhaps he was confused about which car he pulled over and any number of other things. No guarantees, though. At the very least you should get the lower fine for the smaller infraction, but I would also argue that the margin of error in your speedometer plus some assumed margin of error on the officer's equipment might mean you were barely speeding, if at all, and in any case did not warrant even a stop. You have to decide what this is worth to you.

