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                        Methods and Practices for Setting Speed Limits: An Informational Report


            
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                Background
In 1885, Karl Friedrich Benz revealed the first gasoline-powered automobile on the public street system.1 The fastest his car could go was about 13 mph (21 km/h). Since that time, advances in science and technology have brought faster vehicles and better roads, both of which have served to increase travel speeds for automotive travel. Today, attainable speeds are far higher than the maximum speeds that society generally accepts as reasonable for motorized travel on public streets, yet the speedometers on most motor vehicles display maximum speeds that far exceed the maximum legal speed limits on most roads.

Speeding, commonly defined as exceeding the posted speed limit or driving too fast for conditions, is a primary crash causation factor across the globe. Based on a survey of road safety performance, speeding is the number one road safety problem in many countries, often contributing to as many as one-third of fatal crashes and serving as an aggravating factor in most crashes.2 According to the National Highway Traffic Safety Administration (NHTSA), speeding-related crashes account for over 13,000 fatalities per year in the United States, making speeding one of the most often-cited contributing factors for fatal crashes.3

One of the most frequently used methods of managing travel speeds is the posted speed limit. The setting of speed limits predates the automobile by some 200 years, when Newport, Rhode Island, prohibited the horses galloping on major thoroughfares to prevent pedestrian deaths. Similarly, Boston, Massachusetts, limited horse-drawn carriages to "foot pace" on Sundays to protect church-goers.

The English Parliament is credited with setting the world's first speed limit for mechanically-propelled vehicles in 1861.* At that time, the Locomotive Act (automobiles were considered "light locomotives") limited the speed of all "locomotives" on public highways to 10 mph (16 km/h)-5 mph (8 km/h) through any City, town, or village.4 The Act was later amended to set speed limits of 4 mph (6 km/h) outside of towns and 2 mph (3 km/h) within them. These new operating speeds also required three operators for each vehicle—two traveling in the vehicle and one walking ahead and carrying a red flag to warn pedestrians and equestrians.5

Selecting an appropriate speed limit for a facility can be a polarizing issue for a community. Residents and vulnerable road users generally seek lower speeds to promote quality of life for the community and increased security for pedestrians and cyclists; motorists seek higher speeds that minimize travel time. Despite the controversy surrounding maximum speed limits, it is clear that the overall goal of setting the speed limit is almost always to increase safety within the context of retaining reasonable mobility.

The principal exception to the safety objective of speed limits was the oil crisis in the early 1970s, when speed limits were lowered as a means of conserving fuel. This rationale for lower speed limits was revived in Spain in early 2011, where the government lowered the maximum speed limit of 75 mph (120 km/h) to 70 mph (110 km/h) in an attempt to curb fuel consumption in the face of rising oil prices.6 However, the measure lasted only four months before the top speed limit was returned to the former 75 mph (120 km/h).

Maximum speed limits are laws; therefore, speed limits are set for the protection of the public and the regulation of unreasonable behavior on the part of individuals.

* This still predates the gasoline-powered automobile and was enacted for steam-powered vehicles.
      
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                Book:Methods and Practices for Setting Speed Limits: An Informational Report
              Background
                Purpose & Scope
                Report Organization
                The Safety of Speed
                Speed Limit Basics
                Speed Limit Sign and Placement
                Speed Study Data Collection
                Speed Limit Enforcement
                Case Studies
                Summary of Results
                References
                Appendix A: Glossary
                Appendix B: Example Traffic Control Order
                Appendix C: Illinois Policy on Setting Speed Limits
                Appendix D: Northwestern Speed Zoning Technique
                Appendix E: Speed Limits New Zealand (Road Risk Methodology) U.S. DEPARTMENT OF TRANSPORTATION

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