70 in a 60 zone is classic definition of speeding by 10 mph over the limit. You have no defense. That the other cars increased speed does not create a legal exception for you to exceed the zone limit.
It's not a great idea to represent yourself in traffic court. You do, however, have the constitutional right to do so. I would recommend spending an entire day in the traffic court to observe how judges handle self-represented defendants to get an idea of how irritated they get at amateur lawyering. If you really want to represent yourself, you should purchase an hour of a traffic attorney's time to have her or him coach you on how to handle things.
A better choice is simply to hire an attorney.