Speed limits on publicly dedicated and county maintained roads in Larimer County are set based on several important criteria and changes must be supported by an engineering study. Some of the criteria used when setting or changing speed limits include:
- Sight Distance (how far you can see) - Sight distance is how far a driver can see an object lying in the roadway. Sight distance is affected by curves, hills and dips. This distance corresponds to a maximum safe speed for that section of roadway.
- Prevailing Vehicle Speeds - Measurements of vehicle speeds are taken during representative times of the day. The 85th percentile speed (85 out of 100 vehicles are traveling at this speed or slower) is compared with the posted limit.
- Roadside Congestion (number of driveways and intersections) - The amount of roadside congestion affects how safely traffic can travel along a given piece of road. The more congestion, the more opportunity for accidents and near-misses. The primary problem being conflicts between fast moving vehicles on the road and slower traffic entering or exiting the roadway.
- Surrounding Land Use (agricultural, residential, commercial, etc.) - Acceptable traffic speeds are lower in residential areas than in agricultural or open areas.
- Condition of the Road Surface - If a roadway is smooth it can support a higher traffic speed than if it is rough.
- Traffic Accidents - As traffic accidents increases (in number or severity) along a stretch of road the types of accidents are reviewed to see if the speed limits are potentially contributing to their number or severity.
- Law Enforcement/Accident Reduction - The Colorado State Patrol and Larimer County Sheriff may request changes in speed limits.
- Speeds on Adjacent Road Sections - Wherever possible, speed limits are set for significant roadway section lengths (often at least a mile).
Rarely will one of these criteria be adequate to justify a speed limit change. To balance the needs of the general public with adjacent property owners and customers it is often necessary to look at the "big picture" as well as the spot locations.