Speed limits in the United States

Speed limits

This table contains the most usual posted daytime speed limits, in miles per hour, on typical roads in each category. The values shown are not necessarily the fastest or slowest. They usually indicate, but not always, statutory speed limits. Some states and territories have lower truck speed limits applicable to heavy trucks. If present, they are usually only on freeways or other high-speed roadways. Nevada and Washington allow for speeds up to 80 and 75 miles per hour (129 and 121 km/h) respectively, but the highest posted signs are 75 and 70 miles per hour (121 and 113 km/h) respectively. Mississippi allows speeds up to 80 mph (130 km/h) on toll roads, but no such roads exist. Oklahoma removed the maximum speed of 75 from its laws, though no road been posted higher than 75.

History

One of the first speed limits in what would become the United States (at the time, still a British colony) was set in Boston in 1701 by the board of selectmen (similar to a city council):

Ordered, That no person whatsoever Shall at any time hereafter ride or drive a gallop or other extream pace within any of the Streets, lanes, or alleys in this Town on penalty of forfeiting three Shillings for every such offence, and it may be lawfull for any of the Inhabitants of this Town to make Stop of such horse or Rider untill the name of the offender be known in order to prosecution

Federal speed controls

In response to the 1973 oil crisis, Congress enacted the National Maximum Speed Law that created the universal 55 miles per hour (89 km/h) speed limit. Whether this reduced gasoline consumption is debated and the impact on safety is unclear; studies and opinions of safety advocates are mixed.

The law was widely disregarded by motorists, even after the national maximum was increased to 65 miles per hour (105 km/h) on certain roads in 1987 and 1988. In 1995, the law was repealed, returning the choice of speed limit to each state.

Minimum speed limits

In addition to the legally defined maximum speed, minimum speed limits may be applicable. Occasionally, there are default minimum speed limits for certain types of roads, generally freeways.

Comparable to the common basic speed rule, most jurisdictions also have laws prohibiting speeds so low they are dangerous or impede the normal and reasonable flow of traffic.

Truck speed limits

Some jurisdictions set lower speed limits that are applicable only to large commercial vehicles like heavy trucks and buses. While they are called "truck speed limits", they generally do not apply to light trucks.

Theory

The research record is mixed. A 1987 study finds that crash involvement significantly increases when trucks drive much slower than passenger vehicles, suggesting that the difference in speed between passenger vehicles and slower trucks could cause crashes that otherwise may not happen. Furthermore, in a review of available research, the Transportation Research Board (part of the United States National Research Council) states "[no] conclusive evidence could be found to support or reject the use of differential speed limits for passenger cars and heavy trucks" (page 11) and "a strong case cannot be made on empirical grounds in support of or in opposition to differential speed limits" (page 109).

One study has claimed that two thirds (67%) of truck/passenger car crashes are the fault of the passenger vehicle.

Night speed limits

The basic speed rule requires drivers adjust speeds to the conditions. This is usually relied upon to regulate proper night speed reductions, if required. Numeric night speed limits, which generally begin 30 minutes after sunset and end 30 minutes before sunrise, are occasionally used where, in theory, safety problems require a speed lower than what is self-selected by drivers.

Examples include:

Some states create arbitrary night speed limits applicable to entire classes of roads. Until September 2011, Texas had a statutory 65 mph (105 km/h) night speed limit for all roads with a higher limit. Montana has a statutory 65 mph (105 km/h) night speed limit on all federal, state, and secondary roads except for Interstates.

Financial concerns

Traffic violations can be a lucrative income source for jurisdictions and insurance companies. For example:

Thus, an authority that sets and enforces speed limits, such as a state government, regulates and taxes insurance companies, who also gain revenue from speeding enforcement. Furthermore, such an authority often requires "all" drivers to have policies with those same companies, solidifying the association between the state and auto insurers. If a driver cannot be covered under an insurance policy because of high risk, the state will assume that high risk for a greater monetary amount; thus resulting in even more revenue generation for the state.

When a speed limit is used to generate revenue but has no safety justification, it is called a speed trap. The town of New Rome, Ohio was such a speed trap, where speeding tickets raised up to $400,000 per year to fund the police department of a 12-acre village with 60 residents.

Environmental concerns

Reduced speed limits are sometimes enacted for air quality reasons. The most prominent example includes Texas' environmental speed limits.

Metric speed limits

Though not common in the United States, a speed limit may be defined in kilometers per hour (km/h) as well as miles per hour (mph). The Federal Highway Administration's Manual on Uniform Traffic Control Devices, which provides guidelines for speed limit signage, states that "speed limits shown shall be in multiples of 10 km/h or 5 mph." If a speed limit sign indicates km/h, the number is circumscribed and "km/h" is written below. Prior to 2003, metric speed limits were designated using the standard speed limit sign, usually with yellow supplemental "METRIC" and "km/h" plaques above it and below it, respectively.

In 1995, the National Highway System Designation Act prohibited use of federal funds to finance new metric signage.

Definition of speeding

Either of the following qualifies a crash as speed-related in accordance with U.S. government rules:

1. Exceeding speed limits.
2. Driving too fast for conditions.

Speeds in excess of speed limits account for most speed-related traffic citations; generally, "driving too fast for conditions" tickets are issued only after an incident where the ticket issuer found tangible evidence of unreasonable speed, such as a crash.

A criticism of the "exceeding speed limits" definition of speeding is twofold:

1. When speed limits are arbitrary, such as when set through political rather than empirical processes, the speed limit's relationship to the maximum safe speed is weakened or intentionally eliminated. Therefore, a crash can be counted as speed-related even if it occurs at a safe speed, simply because the speed was in excess of a politically determined limit.
2. The effective limit may still be too fast for certain conditions, such as limited visibility or reduced road traction or even low-speed truck rollovers on exit ramps.

Variable speed limits offer some potential to reduce speed-related crashes. However, due to the high cost of implementation, they exist primarily on freeways. Furthermore, most speed-related crashes occur on local and collector roads, which generally have far lower speed limits and prevailing speeds than freeways.

Prima facie

Most states have absolute speed limits, meaning that a speed in excess of the limit is illegal per se. However, some states have prima facie speed limits. This allows motorists to defend against a speeding charge if it can be proven that the speed was in fact reasonable and prudent.

Speed limits in Texas, Utah, and Rhode Island are prima facie. Some other states have a hybrid system: speed limits may be prima facie up to a certain speed or only on certain roads. For example, speed limits in California up to 55 mph, or 65 mph on highways, are prima facie, and those at or above those speeds are absolute.

A successful prima facie defense is rare. Not only does the burden of proof rest upon the accused, a successful defense may involve expenses well in excess of the cost of a ticket, such as an expert witness. Furthermore, because prima facie defenses must be presented in a court, such a defense is difficult for out-of-town motorists.