Traffic Laws: Federal Government's Power And Limits

Traffic laws in the United States are primarily outlined by state law, with each state creating its own vehicle code. However, federal regulations do play a role in shaping traffic laws. The Federal Highway Administration, pursuant to the Highway Safety Act of 1966, requires states to adopt substantially similar standards for signs, signals, and road markings based on the Manual on Uniform Traffic Control Devices (MUTCD). Federal agencies with their own facilities, such as national parks and military posts, also have the authority to implement their own traffic laws on those properties. Additionally, federal regulations set by the National Highway Traffic Safety Administration (NHTSA) govern vehicle safety standards and highway safety regulations. While states have the autonomy to set their own speed limits and traffic rules, they must remain in substantial conformance with federal standards, allowing for some local variations.

Speed limits

However, it is important to note that the federal government has intervened in speed limit legislation in the past. In response to the 1973 oil crisis, the National Maximum Speed Limit (NMSL) was enacted as part of the 1974 Emergency Highway Energy Conservation Act. This federal law prohibited speed limits higher than 55 mph (89 km/h) and required states to agree to this limit to receive federal funding for highway repair. This uniform speed limit was in place until 1995, with some states challenging it and proposing deals for exemption. In 1987, Congress permitted states to raise speed limits to 65 mph (105 km/h) on rural interstate highways.

In addition to statutory speed limits, there are also posted speed limits, which are sign-posted along roads and are enforceable by law. These posted speed limits can be established by cities, counties, or state transportation agencies as adjustments to the statutory speed limits. Some cities and counties will set a blanket speed limit for roads within their jurisdictions, which are generally posted at city or county lines.

Traffic signs

The Manual on Uniform Traffic Control Devices (MUTCD), first released in 1935, has significantly influenced the road signs used in the US and other countries in the Americas. The MUTCD covers a range of sign types, including warning signs, regulatory signs, and traffic signal-related signs. For instance, the MUTCD's W series covers warning signs relating to curves, turns, intersections, advance traffic controls, divided highways, hills, and grades. The W series signs are usually orange and meant for temporary use in construction zones. The R series, on the other hand, covers bicycle and pedestrian signs, traffic signal-related signs, weight limit signs, and more.

However, the MUTCD does not cover all situations, and several states have their own standards in addition to the MUTCD. For example, some states have their own warning signs relating to speed humps, the lack of traffic signs, and the end of a controlled-access highway.

In the US, road signs are used to regulate traffic, provide directions, and warn road users of potential hazards. Stop signs, yield signs, and speed limit signs help control the flow of traffic, while directional signs, route markers, and destination signs assist road users in finding their way. Warning signs, construction signs, and animal crossing signs alert users to potential dangers and help them take necessary precautions. Additionally, road signs enforce laws and regulations, such as no parking, no U-turn, and no entry restrictions.

Traffic lights

Traffic laws are created by the state and are enforced by police officers observing traffic and issuing citations to motorists who violate the signal. In the United States, the National Highway Traffic Safety Administration (NHTSA), which is part of the U.S. Department of Transportation, administers statutory authority and issues Federal Motor Vehicle Safety Standards to implement laws from Congress. These standards can be found in Title 49, Part 571 of the Code of Federal Regulations. The NHTSA also sets vehicle safety regulations, found in Title 49, and highway safety regulations, found in Title 23 of the Code of Federal Regulations.

In some jurisdictions, there are ordinances or by-laws against "gridlocking". For example, in New York City, a motorist entering an intersection, even on a green light, who gets stranded in the intersection and remains there after the light turns red, blocking traffic from other directions, may be cited. In some American states, a vehicle already in the intersection when the light turns red legally has the right of way, and vehicles with a green light must yield. In all 50 states, drivers are allowed to turn right on red after coming to a full stop and yielding to all other traffic and pedestrians.

Red light cameras are used in some countries to photograph vehicles and drivers crossing against the light, resulting in a fine for either the driver or the vehicle's owner. While these cameras can reduce the number of crashes, they have also been abused by local governments, with vehicle operators fined as a result of improperly modified traffic systems.

Vehicle registration

For vehicles leased or owned by the Foreign Mission Community and operated within the US, registration must be done with the Office of Foreign Missions. This process also includes obtaining the appropriate license plates and decals. In the case of leased vehicles, adherence to the loan or leasing agreement is crucial, as non-payment may result in the creditor's right to repossess the vehicle. Prior to repossession, it is recommended to contact the Diplomatic Motor Vehicle program for guidance to avoid any violations of international law.

Additionally, specific regulations are in place for identifying and registering government motor vehicles. These vehicles are required to display US government license plates until they are removed from government service, transferred outside the agency, or the plates need replacement due to damage. The use of US government license plates is exclusive to the assigned government motor vehicle and should not be transferred to another. In the case of loss or theft of license plates, it is mandatory to report the incident to the local security office, local police, and the Federal Government Motor Vehicle Registration System.

It is worth noting that certain exemptions exist regarding the display of government license plates and motor vehicle identification. The head of an agency or their designee may authorize a limited exemption upon written certification stating that identifying the vehicle would compromise security or the agency mission. This exemption can be granted for a period ranging from one day up to three years, after which re-certification is required if the exemption is still necessary. Motor vehicles assigned for the use of the President and the heads of executive departments specified in 5 U.S.C. 101 are also exempt from displaying motor vehicle identification. Instead, they display regular license plates of the state, commonwealth, territory, or possession of the US where the vehicle is primarily operated.

Seat belt laws

In the United States, most seat belt laws are left to individual states. The first seat belt law was a federal law, Title 49 of the United States Code, Chapter 301, Motor Safety Standard, which came into effect on January 1, 1968. This law mandated that all vehicles (excluding buses) be fitted with seat belts in all designated seating positions. Since then, the law has been amended to require three-point seat belts in outboard-seating positions and, ultimately, three-point seat belts in all seating positions.

While the use of seat belts was initially voluntary, New York became the first state to mandate their use on December 1, 1984. As of 2025, New Hampshire is the only state without a law requiring adults to wear seat belts in a vehicle.

Seat belt use laws can be subject to primary or secondary enforcement. Primary enforcement enables law enforcement officers to stop and ticket a driver if they observe a violation. On the other hand, secondary enforcement means that an officer can only stop or cite a driver for a seat belt violation if the driver has committed another primary violation, such as speeding or running a stop sign.

As of 2024, 41 states, the District of Columbia, and two territories have laws enforcing rear seat belt use. Of these, 18 states, the District of Columbia, and two territories have primary enforcement for all occupants. In contrast, 11 states include rear seats under secondary enforcement, and six states have secondary laws for adult front-seat occupants.

Seat belt warning systems, also known as reminder systems, employ visual and audible alerts to encourage seat belt use. These systems are designed to increase seat belt usage, especially for rear-seat passengers.

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