I'm hoping someone else here will have the details on the source and update periods.

I will say that we were traveling through Raleigh/Durham/Chapel Hill during rush hour on a Friday evening and we turned to the RTTI to find out about delays or accidents. The RTTI told us EXACTLY where the accident/back-up was located (used exits as reference points), told us which lanes were closed in the accident and gave an estimated time for the delay. The information was SO up to date that at one point it told us that we should re-route due to an accident on the highway about 15 miles ahead of us. When we re-calculated the route a few minutes later, there was no warning symbol on the map and it took us back to the original route. When we passed through the area where the wreck had been located, they were cleaning up debris. It was so accurate that it knew that there had been a wreck AND that it had been cleared up and traffic was flowing smoothly.