You're invisible to them. They will slam you into a wall, unintentionally spin you out, and slam into the back of you. It's some of the worst AI I've seen since in a long while.
I'm trying my best to avoid stepping into each other car's line. It doesn't matter. Be as careful as you want. Give them as much respect as you want. They'll slam into you and you'll find yourself scrambling to reset the race.
Since, like all GT6 races, you've only got a hilariously small number of laps, there's no coming back from it. You have to restart the race.
So, I just rage quit the game.
I hate their structured career mode. Because of the short laps you're either powering up your car so that it's much, much faster than the AI vehicles, or you're bullying the other cars out of the way as you rush to climb to first from last in such a short period of time. There isn't enough time for strategy, and thus the racing is never as engaging as it could be.