[dentist90]

His accepting the ticket is not an admission of guilt. As one posted, the roadside is not the place to dispute an alleged offense. If the cops were of the mind that they were going to cite you I doubt you would have talked them out of it. I suspect that if you two were evasive about who was driving they may have upped the ante and taken the two of you to the station and made your lives miserable for a couple of hours, taking statements and launching lots of paperwork even without the likelihood of a charge being laid.
If your friend saw flashing lights at an accident scene and blew right past it I think he should do the right thing. Maybe try to get the charges reduced. On the other hand, if there was no visible accident scene warnings ( flags, pylons, reduce speed signs, police with their light bars on, etc) your friend should contest it. Even a speeding charge will be hard to pursue if there is no way to determine what speed you were travelling.
In my experience (my dad was a police officer) you may dodge a ticket at the roadside if the infraction isn't too severe and you're civil when speaking to the officer. But if they've decided the infraction was serious, your arguing with them will only make it worse. Then you may get the complimentary 'vehicle inspection'. I don't know of anyone who argued their way out of a ticket, but a few have apologized their way out!