Simulate night time traffic in a city

Hi community!

I am new to Motion 5 and been searching youtube for answer to my question but havent come so close.

I would like to simulate a night traffic where multiple car`s headight are shown with a following trail of light that slowly fade off.

Done a demo to show what I mean. http://youtu.be/kQsQ40QYDvo Its done with a bezier line and "write on" behavior.

Hopeing for an answer, thanks!

//örjan