Chapter 4. Uniform Vehicle Code

This chapter details Uniform Vehicle Code (UVC) chapter 11 and variations and inconsistencies among different States and jurisdictions.

Introduction of Uniform Vehicle Code Chapter 11

The rules of the road are under the authority of State legislatures to enact, which makes them difficult to enforce uniformly across all States. The UVC was a publication developed by the National Committee on Uniform Traffic Laws and Ordinances (NCUTLO). It was designed to provide a comprehensive guide of traffic and vehicle codes for States to use as they develop motor vehicle and traffic laws.⁸³ The UVC was last updated in 2000.⁸⁴

UVC chapter 11 addresses traffic laws and is relevant to automated driving system (ADS) operational behavior and traffic regulation. Table 3 lists the areas of guidance from chapter 11.

Table 3. Uniform Vehicle Code chapter 11 sections.

Article I	Obedience to and Effect of Traffic Laws
Article II	Traffic Control Devices
Article III	Driving on Right Side of Roadway – Overtaking and Passing – Use of Roadway
Article IV	Right of Way
Article V	Pedestrians' Rights and Duties
Article VI	Turning and Starting and Signals on Stopping and Turning
Article VII	Special Stops Required
Article VIII	Speed Restrictions
Article IX	DUI and Other Serious Traffic Offenses
Article X	Stopping, Standing, and Parking
Article XI	Miscellaneous Rules
Article XII	Operation of Bicycles, Other Human-Powered Vehicles, and Mopeds
Article XIII	Special Rules for Motorcycles
Article XIV	Streetcars
Article XV	Victims of Traffic-Related Offenses
Article XVI	“Safe Streets Act” – Vehicle Immobilization Resulting from Continuing to Drive When the Driver's License Is Suspended or Revoked for DWI or DUI

DUI = driving under the influence. DWI = driving while intoxicated.
Source: Uniform Vehicle Code, 2000.

Not all of chapter 11 articles and recommended rules will apply to ADS, such as Article XV, Victims of Traffic-Related Offenses.

The UVC has not been updated since 2000. In 2015, draft updates were proposed, but no additional efforts have been made to keep the UVC up to date. Most States have already adopted their traffic laws and the Internet has made individual laws more easily accessible to the public and to other State legislatures.

Variations in Traffic Rules Among States and Territories

The UVC was developed by members who represented many State governments and related organizations. As a result, the guidance codes the UVC contains are similar to the final rules that most States have adopted. However, there are some variations in traffic rules among States.

For decades, the American Automobile Association (AAA) has reviewed and summarized the different motor vehicle laws across the United States and Canada. The AAA Digest of Motor Laws⁸⁵ is a searchable online database of these laws and rules on driving and owning a motor vehicle (including traffic laws, vehicle titling and registration requirements, fees and taxes, driver’s licenses, and traffic safety).

For some traffic safety laws—for example, impaired driving—there is not much variation among States. According to the Digest of Motor Laws, “All 50 states and the District of Columbia have impaired driving laws that prohibit the operation of a motor vehicle while under the influence of intoxicating beverages, with the illegal per se limit set at 0.08 percent blood alcohol content (.08 BAC). All 50 states and the District of Columbia set the legal drinking age at 21.”⁸⁶ Even with a traffic safety law that is similar among all States, such as impaired driving, there are still differences between States on the use of ignition interlocks for impaired drivers.

The differences for other traffic safety laws vary from State to State, which would require an ADS to learn the rules of each State. For example, Figure 7 illustrates the differences, by State, for hazard light use, which range from being permitted while driving to not permitted while driving or with exceptions. In this case, ADS must be aware of which State it is operating in and adjust its operational behavior accordingly.

Following distance is another traffic safety law that varies by State. The UVC guidance is, “Do not follow another vehicle more closely than is reasonable and prudent” (Article III: Driving on the Right Side of Roadway – Overtaking and Passing – Use of Roadway).⁸⁸ New York State recommends using a “two-second rule” to allow space to stop.⁸⁹ California recommends using a “three-second rule” to avoid tailgating.⁹⁰ Florida⁹¹ and Pennsylvania⁹² instruct drivers to keep a minimum 4-second following distance. Florida has a separate following-distance requirement of 300 feet for trucks or any vehicle towing another vehicle.⁹³

Headlight use requirements also vary by State. Most States require headlight use between sunset and sunrise, with some States requiring use only one-half hour after sunset to one-half hour before sunrise. For example, some States also specify that headlights should be used when visibility is less than 500 feet, while some specify less than 1,000 feet. Some States also specify that headlights must be used whenever windshield wipers are turned on.

Variations in Dynamic or Local Traffic Laws

Time-of-day speed limits are regulatory, such as in construction work zones or when children are present near a school. They are predictable, which makes them less dynamic than truly traffic-dependent speed limits.

Dynamic, traffic-dependent regulations may vary by State. At least 15 States use variable speed limits (VSL).⁹⁴ These VSLs may be regulatory (enforceable) or advisory (but still subject to the fundamental speed rule) depending on the State. For example, Wyoming’s VSL law is regulatory (strictly enforced).⁹⁵ Washington State allows local authorities to establish or alter maximum speed limits, stating that “Any altered limit established as hereinbefore authorized shall be effective when appropriate signs giving notice thereof are erected. Such maximum speed limit may be declared to be effective at all times or at such times as are indicated upon such signs; and differing limits may be established for different times of day, different types of vehicles, varying weather conditions, and other factors bearing on safe speeds, which shall be effective when posted upon appropriate fixed or variable signs.”⁹⁶

Dynamic congestion-based tolls are regulatory to the extent that the vehicle owner gets a ticket in the mail if the vehicle does not have a toll tag or the required number of people in the vehicle to avoid the toll or pay a reduced toll. In California, low emission vehicles and zero emission vehicles displaying a special-issued decal may use the high-occupancy vehicle (HOV) lanes, even if they do not have the required number of people in the car.⁹⁷ ADS may need to decide if the vehicle is eligible to use the express lane (i.e., has a toll tag, has the minimum number of occupants, or is otherwise eligible).

Examples of other dynamic regulations that may vary by day of week, time of day, or road or weather conditions include:

• Using wipers when it rains.
• No parking on the street on certain days during overnight street-sweeping hours.
• Curb parking lane opened up to traffic during peak hours (typical in older downtowns).
• Obeying police officers directing traffic.
• Pulling over and stopping when ambulances, fire trucks, or police sound their sirens.
• Not crossing a flooded wash (Arizona law for dealing with flash floods).⁹⁸
• Stopping when a school bus stops and flashes its red lights.
• Daytime versus nighttime freeway speed limits.
• Chains required to go over a summit during winter snowstorms.
• Lower speed limit when chain controls are in place.

Local authorities may also assign traffic laws that differ from the State laws. In New York State, a right turn on red is permitted at signalized intersections unless there is a no-turn-on-red sign posted. However, New York City does not permit a right turn on red unless there is a sign that permits it.⁹⁹