Creating car light trails using "Stroke path with brush"

[victorramirez]

Hi! I want to create some car light trails for a matte painting scene.

 

I'm using a "Stroke path with brush", applying Shape Dynamics so the brush size is reduced as it approaches the vanishing point of the scene (1st image).

 

However, when I use a Round Blunt tip (to produce a more realistic effect simulating the light trails of several cars, 2nd image), I'm not able to apply Shape Dynamics for the brush size (3rd image).

 

Do you know any other brush tip that could produce a realistic effect (such as in the 4th image), while also being able to reduce its size via Shape Dynamics?

 

Thank you!