Why does the nav on this car always head me into the traffic jams?

I generally hit in fastest routes, but it seems like it will head me towards the traffic jams and not try to avoid them? I've got good at second guessing it and doing the opposite of what it tells me to do and save a lot of time this way. Today I was heading down rt 41 and it even said there was a traffic jam ahead and was telling me I'd be home at 2:05 PM. I cut headed up a little east to I 75 and it was a clear shot home with no traffic jam and I made it home by 1:50 PM. The GPS all the way back home kept trying to cut me off I75 back onto 41 which run along side it but still showed yellow under traffic and said there was a traffic jam, strange. You'd think since I programmed it as the fastest route it would try to avoid the traffic jam? I could see if I programmed it for the shortest route or something? Any ideas?