The board of county commissioners may set speed zones altering [statutory] speeds, both
         as to maximum and minimum, after investigation determines such a change is reasonable
         and in conformity to criteria promulgated by the Department of Transportation, except
         that no such speed zone shall permit a speed of more than 60 miles per hour.

The criteria promulgated by DOT pursuant to this statute are contained in a manual entitled
"Speed Zoning for Highways, Roads, and Streets in Florida."  Sheriff Turner referred to this
manual and questioned whether the Commission could lower the speed limits on all graded roads
county-wide.  The Sheriff raises a good question.

The procedure that a local government is to follow pursuant to this manual seems geared towards
determining the safe driving speed on a given roadway.  This procedure involves doing studies to
determine the speed at which drivers actually drive on the roadway. The assumption is that 85%
of the drivers will drive at a safe speed, and that this is the speed that most drivers will maintain
regardless of what speeds are posted.  Thus, the DOT's basic position is that speed limits should
be set at the speed at which 85% percent of the drivers travel on a given roadway.

According to the DOT manual, a local government amy deviate from this 85% rule if "there are
road or roadside features not readily obvious to the normally prudent driver" that would make a
lower speed limit advisable.  It is this exception to the general rule that supports the County's
lowering of the speed limits on particular segments of roadways where there are limited sight
distances, dangerous intersections, unusual congestion, and the like.

I agree with the Sheriff's position that the County Commission cannot simply declare that the
statutory speeds are unsafe throughout the County and lower them on all roads.  But, what has
been proposed is not that the speed limits be lowered just to make graded roads more safe, but
rather for the purpose of protecting the integrity of graded roads.  If this is the goal of the lowered
speed limit, then the 85% percent rule does not seem to be relevant.  It may be perfectly safe to
drive at 55 mph on a freshly-graded roadway, but what the 85% driving at this speed would not
be aware of is that a great many people traveling at such speed will cause damage to the
graded roadway that the County cannot afford to repair, and that such damage will create safety
hazards for later drivers on the same roadway.

If the County can show this to be the case, then lowering speeds under such circumstances could
fall under the provision allowing the County to lower speeds to address "road or roadside
features not readily obvious to the normally prudent driver."  Although DOT would probably
frown on the County doing this for all graded roads county-wide, the County may be able to get
DOT to agree that speeds could be lowered on specific roadways where the posted speeds are
causing the worst roadway degradation.