I suggest you request the cops description of the incident and then run some numbers.
Calculate the distance he said you travelled in the amount of time he stated. See if it adds up of if there are any big holes in his story. How did he get the speed? If it wasnt by radar/laser then you have a chance. Not a good one but a chance.
If you have a good driving record then you have a very good chance of them dumping it to a parking ticket.
A lawyer will cost $400 minimum