According to TFA, the Federal guidelines recommend times based on the posted speed limit or the 85th percentile of actual speed, whichever is greater. Florida is ignoring/removing the "whichever is greater" clause.
In most cases, one can assume that the 85th percentile is greater than the posted limit, in which case the times are based on the posted limit. The ones at risk of a ticket are speeding drivers. But reading the article literally, there is another possibility. If the 85th percentile of actual speed is *less* than the limit (as in a congested area), FDOT is free to time yellow lights according to the 85th percentile, and *below* what the posted speed limit would require. Such an action would put drivers who are otherwise law-abiding at risk for tickets.