In general, the race transportation is good to great. However, EVERY year Mears has a snafu or two. Frankly, I am shocked that there are not more. Roads are closed, GPS units then give incorrect instructions and runners are notorious for waiting til the very last moment. Usually one resort will be picked on as the resort of the year. 2012 seems to have been POR, 2011 was SSR, 2010 was most resorts due to the cold. I was nearly left at the Yacht Club in 04 when I was meeting a running buddy who was running a little late. That really did not matter as the buses did not stop between 3:40and 4:20. Mears has a roving dispatcher who arrived and within a few moments 10-12 buses followed. In 2003 (I think) the race was delayed 30 minutes due to a huge traffic issue.
When driving, the traffic will usually seem normal until one approaches the intersection of World and Epcot. That is generally where one spends the extra time on race morning. Normally, the traffic is not all that bad, but on occasion there will be a snag. With the new marathon course, the road closure on the inbound road from World to Epcot Parking should not need closed, so some of the pressure may be off.
I would suggest with all seriousness that one should attempt to be on the bus or in the car (when on property) no later than 0330, a little earlier is better. The 0300-0400 traffic window was set up when the race started at 0600. The window has not changed, but the race numbers are greater and the start time 30 minutes earlier. You never know when your resort will be the resort that has its time in the barrel. The only resorts that I would go later are the monorail resorts. I think in 2010 I left at 0420 from the Contemporary. I had little to no time in the staging area. Generally, hopped of the rail, walked to the tents, shed my keeper warm ups and then walked to the corral as the National Anthem was beginning. Not a lot of time to spare.
Last year had the added issue of a new return route for buses during the half. Since both sides of Epcot are closed during most of the half, there is no ‘normal’ path into the parking lot. They attempted to run buses in on the Cast Member side of the parking lot via Overpass Road and Woodpecker Lane. Surprise, it failed to work well. I am betting that will be much improved in 2013.
Inevitably, the traffic leaving Epcot parking seems to back up on the even years. We have waited for 45 minutes just to get out of the parking grid. Since this is an odd year coming up, it should not occur…
Good luck. I am sure that there are numerous stories of those who wait to the last minute with no issue.