This seemed to work out well tonight. To make a burst of tracer coming down the street, I inserted a cylinder, reduced it, stretched it out {unstretched didn't look right...didn't 'streak'] added color and glow. and stacked up seven of them at the end of the street...somewhere around -50 in. on the Y axis. Then, at Frame X, I sent one down the street to +30 on the Y. Travel time: 4 frames. Every 4 frames after, I sent another, each one arriving 1 inch higher, and 1 inch to the right of its predessor. Otherwise they follow each other 'nose-to-toes' and look too regular. Once a burst looks good, duplicate the keyframes and hammer the neighborhood.