Speed limits are the road’s most basic rule — protecting motorists from themselves by way of one simple number. Whether people abide by them, however, is up to the authorities’ ability to find the number most effective for saving lives and most reasonable for drivers to do so.
And the process is anything but arbitrary.
Traffic attorneys from Springfield, IL note that more than being effective, speed limits need to be fair, and such is the goal behind every number you see along major roads today. These numbers serve as bases for enforcement and hence require the exact maximum reasonable and safe operating speed under favorable conditions. Every single one.
While some variables are harder to pin down compared to items such as a highway’s features and overall design, the introduction of dynamic message signs allow authorities to update speed limits immediately during inclement weather, construction work, or congestion in connecting roadways.
For highways with static speed limit signs, however, the U.S. Department of Transportation Federal Highway Administration (FHWA) lists the following factors that local authorities incorporate to their rulings:
- A vehicle’s mechanical condition and characteristics
- Driving ability/capabilities
- Traffic volume: vehicles, pedestrians, and bicycles
- Weather and visibility
- Roadway design elements, including:
- Road function/purpose
- Lane and shoulder width
- Horizontal and vertical curves
- Available sight distances
- Driveways with restricted visibility and other roadside developments
- High driveway density
- Rural residential or developed areas
- Paved or improved shoulders
- Pavement conditions
- Crash frequency and severity
The FHWA mentions how the geometric design features of the road and roadside activity heavily influence the abovementioned factors since drivers tend to select operating speeds based on the visual scene present. For instance, drivers would behave differently on narrow, winding roads than on a straightaway, much like how they slow down on a bustling pedestrian-filled area than in locations where there is little to no risk of collision.
For many of the country’s roads, speed limits are easy — if not outright tempting — to ignore. But, in anywhere other than an empty highway on a bright sunny day, following that one precisely determined number makes all the difference.