What is the Roadside clear zone?
The Florida Department of
Transportation states "The roadside clear zone is that area outside the traveled
way, available for use by errant vehicles". The roadside clear zone is an area
in the median or on the side of the road, off the pavement. That is kept clear
of fixed objects. If vehicles drive off the road, for whatever reason, the
drivers have leeway to regain control of the vehicle and steer back onto the
road. The clear zone also permits disabled vehicles to pull off the roadway.
Clear zones are established to provide an extra margin of safety for
travelers.
Minimum clear zone standards have been specified by the Florida Department of Transportation for the design of roadways. New highways always include clear zones when the are built. The width of the clear zone depends upon the type of roadway, the speed of vehicles traveling on the roadway, and several other criteria. Rural Interstate highways, with heavy traffic and high speeds, should have a clear zone at least 30 feet wide. A city street with curbs and a 35 mph speed limit requires a minimum 2 ½ feet of clear zone behind each curb. Other clear zone widths are specified for each different type of road. Clear zones should be wider along the outside edge of curves, since out-of-control vehicles are more likely to run off that side of the road.
Other elements considered when specifying clear zone width include the slope of the shoulder, the depth of roadside ditches, railroad crossing equipment, and existing structures or buildings that may be very difficult to relocate when a road is widened. Objects that cannot be removed from the clear zone need protective devices like crash cushions or guardrail installed to protect drivers and passengers.
Clear zones can be enhanced with some innovative techniques. Using selected plant species, landscaping can provide a natural crash cushion of thick shrubbery or bushes. Placing electric and telephone lines underground will eliminate concrete poles long the side of the road. Billboards and other large signs can be built using supports that angle away from the roadway. Smaller signs can use special breakaway supports. Street lights can bolt to low-profile concrete foundations. Stormwater drains and culverts can be designed for vehicles to drive over them rather than crash into them.
Trees, business signs, or local landmarks are sometimes identified for relocation during a road widening project in order to provide an adequate clear zone. It is often difficult for residents to accept the need for relocating such objects to accommodate a larger road, but highway designers are responsible to the public for developing the safest practical roadway design.
When you see damaged light poles, heavily scarred tree trunks, or guardrail installed around a chipped concrete foundation and think about the events that caused the damage, you will understand why engineers insist on adequate roadside clear zones.
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