You can either create a white solid and use some form of radial blur (CC Light...something or other...rays? burst?)
Or you could invest in a plugin called Trapcode Lux. (The rest of the Trapcode suite is pretty useful too, especially Particular!)
I downloaded a trial to Trapcode suite, but I was wondering if there is a way to make a shape with the lux light? The headlights I am working with are not circular at all. They are a rectangle, so I don't want circular lights on them!
Lux will just show a beam of light without any real shape from most angles. You can probably get away with it.
You could use Trapcode Shine to make a beam too and that would be based on the shape of the layer. (Or CC Light Burst or whatever it's called.)
Thanks and God Bless