tailgate mate

The complete stranger you meet on the expressway that you follow for long distances at the same speed. Useful as a deterrent for police officers or even as an auxiliary form of cruise control. Although the two of you have never met, a special bond is formed which heightens as the distance you travel together increases.

I'm glad I found that tailgate mate on my way to college. If it wasn't for him I would have never slowed down in time for the fuzz.