The Brief History and Science of Speed Limits

Speed limits are essential in reducing road traffic injuries and fatalities. They play a critical role in traffic management and safety, with the implementation dating back to before the advent of automobiles. In 1652, Newport, Rhode Island, prohibited horses from galloping on major streets to safeguard against pedestrian accidents. Similarly, in Boston, regulations were placed on horse-drawn carriages mandating a slower "foot pace" on Sundays.

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The inception of the gasoline-powered automobile in 1885 introduced a new realm of speed regulation. The vehicle could achieve speeds of up to 13 mph, but today's cars can travel at speeds up to 10 times faster. It's estimated that speeding contributes to one-third of all fatal crashes, which underscores the need for enforced speed limits. Drivers generally accept speed limits as a fundamental component of road safety.

But who decides how fast is too fast? And how are speed limits determined?

Speed Matters

The physics of motion dictates that higher speeds result in more severe accidents. Traffic safety experts have debated for years whether increased speed also leads to a higher crash frequency. This debate is complicated by factors such as road design and driver behavior. However, recent studies strongly indicate that, all other factors being equal, higher speeds do lead to a higher rate of accidents.

Who Sets Speed Limits?

In the United States, both state and local governments are traditionally responsible for setting speed limits. Exceptions have occurred, such as during World War II and the National Maximum Speed Limit of 55 mph established in 1974, which was repealed in 1995. However, there is no universal method for setting these limits, and traffic engineers rely on various techniques and their professional judgment.

Methods for Setting Speed Limits

Different regions use diverse methods to determine speed limits. The primary approaches include:

Engineering Approach, Operating Speed

In this method, engineers set speed limits based on the 85th percentile speed, which reflects the speed at or below which 85% of drivers travel under good conditions. This is done to ensure safety, as traveling at or near this speed minimizes crash risk. It also helps law enforcement target the most egregious speed offenders.

Used in: United States

Engineering Approach, Road Risk

This approach sets speed limits based on the functional classification of the road (urban, rural, etc.), adjusting for specific road conditions and crash history.

Used in: Canada, New Zealand

Expert System Approach

A computer program mimics the judgment of human experts to set speed limits.

Used in: United States, Australia

Optimization

This method strives to minimize societal costs such as accidents, travel time, and pollution. It acknowledges that individual drivers may not consider the broader societal impacts of their speed choices.

No widespread use in any jurisdiction

Injury Minimization/Safe System Approach

The goal here is to set speed limits to manage crash energy in such a way that no individual sustains fatal or serious injuries. This approach prioritizes human safety over reducing fuel consumption or travel time.

Used in: Sweden, Netherlands

Drivers Are in Control

Speed limits guide drivers on acceptable speeds under favorable conditions. It's expected that drivers will lower their speeds during adverse conditions such as poor visibility or the presence of pedestrians and cyclists. Like other driving responsibilities—wearing seatbelts, avoiding phone distractions, or not driving under the influence—adherence to speed limits is crucial.

While speed limits aim to enhance safety, compliance is essential to reducing accidents. If you, or someone you love, have been the victim of a car accident, don't hesitate to get in touch with us. We're available 24/7.

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