Was it not big enough or yellow enough to see?

Things like this seem to happen on a regular basis. I don't know how. This from the Knoxville New-Sentinel:

A Murfreesboro woman was cited for following too closely by Knoxville police after her 1998 Nissan Maxima rear-ended a Sevier County school bus on the University of Tennessee campus Tuesday afternoon.

(snip)

Three students on the bus were sent to Children's Hospital of East Tennessee "just to be checked," DeBusk said. There were 32 students from Seymour Intermediate School on the bus on a field trip to McClung Museum.