As you travel the roads and highways of your community, you may not be aware of all the different speed limits that are in force. You are probably most familiar with posted speed limits because you frequently see them on signs at strategic points along your route. 

You may have also encountered special conditions speed limits without thinking about it or realizing what they are. According to the U.S. Department of Transportation Federal Highway Administration, special conditions speed limits decrease speed around a particular hazard. They can be either temporary or permanent, depending on the nature of the hazard. 

Temporary special conditions speed limits 

When it is necessary to revise the speed limit due to a temporary condition, changeable message signs go up in the area of the hazard to announce variable speed limits. Conditions that may necessitate variable speed limits include traffic congestion, car accidents or inclement weather. Variable speed limits are usually at least 10 miles per hour slower than the posted speed limit. 

A particular type of temporary special condition is road construction. Each work zone will probably have its own speed limit set for the duration of the project to facilitate traffic movement that is efficient and safe for everyone, drivers and workers alike. 

Permanent special conditions speed limits 

These pertain to hazards that are permanent fixtures. For example, the road may have a sharp curve that is dangerous to navigate at high speeds. An advisory speed limit tells you to reduce your speed to a safe velocity to bypass the hazard. It only applies to that isolated area, however. Once you pass it, you can resume normal speed. 

School zone speed limits are in place to protect children from getting hit by a car when they cross the street or if they enter into it unthinkingly while outside during recess. They remain in place as long as there is a school there, but authorities typically only enforce them at times of the day when children are likely to be present.