You might want to look at this report
http://www.cpsc.gov//PageFiles/117813/BikeReport.pdf.
This little snip from the conclusion provides a good summary
The results of the study showed that there was no statistically significant difference in performance among the various reflector treatments and the current CPSC regulation reflectors.
Therefore, improvement to the existing reflector requirement does not appear warranted. The parallel path crash simulation showed that the flashing red LED taillight used in the evaluation could significantly improve a driver's detection distance over the CPSC regulation reflectors.