Chapter 2. Traffic Regulations, Automated Vehicles, and Highway Automation

This chapter introduces national highway automation and automated driving systems (ADS) technologies and behavior.

Automated Driving Systems and Operational Behaviors

As cyber-physical systems, ADS-equipped vehicles can be abstracted into sensing, computing, and actuation modules, as shown in figure 1. Sensing devices, such as laser scanners (light detection and ranging [LiDAR]) and cameras, are typically used for driving automation in urban areas. Actuation modules handle steering and throttle, and the trajectory planning and tracking module typically generate the control commands. Computation is a major component of self-driving technology. Scene recognition, for instance, requires the localization, detection, and prediction modules, whereas path planning is handled by mission- and motion-based modules. Each module employs its own set of algorithms. Combined, the modules are exemplified by the well-known open-source automated driving software, Autoware™. Figure 1 shows the basic control and data flow for an autonomous vehicle. Sensors record environmental information that serves as input data for the artificial intelligence core, which includes data fusion for vehicle localization based on filtering techniques, machine learning methods for predicting other vehicle’s behavior, and intelligent decision-making in mission/motion planning using optimal control or reinforcement learning approaches. Three-dimensional maps are becoming commonplace for self-driving systems, particularly in urban areas, as a complement to the planning data available from sensors. External data sources can improve the accuracy of localization and detection without increasing the complexity of the vehicle’s algorithms. Artificial intelligence cores typically output values for angular and linear velocities, which serve as commands for steering and braking, respectively.

Another important concept related to ADS operational behavior is the operation design domain (ODD). In SAE’s definitions of automation levels, a driving mode is a type of driving scenario with specific dynamic driving task requirements (e.g., expressway merging, high-speed cruising, low-speed traffic jam, and closed-campus operations). In SAE’s levels of driving automation, shown in figure 2, a particular shift occurs from SAE Level 2 to SAE Level 3: the human driver no longer has to actively drive when the corresponding automated driving features are activated. This is the final aspect of the dynamic driving task that is now passed over from the human to the automated system. At SAE Level 3, the human driver still has the responsibility to intervene when asked to do so by the automated system. At SAE Level 4, the human driver is relieved of that responsibility, and at SAE Level 5, the automated system will never need to ask for an intervention.

Source: Autoware

Figure 1. Diagram. Automated driving vehicle platform (Autoware).³

Source: © 2020 SAE International. The summary table may be freely copied and distributed provided SAE International and J3016 are acknowledged as the source and must be reproduced AS-IS.⁴

Figure 2. Illustration. SAE International® definition of levels of automation.

Based on the understanding of ADS software structure, any ADS component under different rules and regulations can affect ADS operational behavior. For example, yellow signal legends and timing may vary along and among urban corridors, such that when an AV detects a yellow light, how it interprets the rule may be dramatically different, which will then change the time when the vehicle can pass the stop bar at the intersection and, in turn, have an effect on the trajectory planning process of the AVs. Another example involves use of the left-most lane on freeways (e.g., overtaking only or regular driving). If the lane can only be used as an overtaking lane, the ADS planning module will always ask the vehicle to change back to the original lane after it passes the front slow-moving vehicle. Compared with the other condition (i.e. used as regular driving lane), this traffic rule will potentially result in frequent lane-change behavior on freeways, causing inefficient traffic operations, demonstrating that different traffic laws and regulations may result in dramatically different ADS behaviors, even with the same ADS software. It is critical to provide ADS vehicles with accurate traffic regulation information and to design ADS software to explicitly incorporate the regulations to ensure safe and efficient behavior.

Additionally, ADS only involves single-vehicle automation through onboard sensing and computing. However, SAE is working on a new standard, SAE J3216_202005™,⁵ to define cooperative driving automation (CDA), which enables and supports ADS automation through machine-to-machine communications. In fact, CDA becomes even more relevant when traffic regulation databases are shared with AVs enabled with CDA to communicate this information. The Federal Highway Administration’s (FHWA) CARMA^SM research platform is designed using open-source software to test CDA concepts to improve transportation system management and operations (TSMO) using CARMA Cloud^SM, a cloud-based framework. Information from databases of traffic regulations can be shared with ADS vehicles enabled with CDA through the cloud or other vehicle-to-infrastructure (V2I) communication.

Emerging Automated Vehicle Data Frameworks

The U.S. Department of Transportation (USDOT) has facilitated agreements among industry and non-Federal governments on common data formats that lower the cost of data exchange. This section focuses on the introduction of two most recent frameworks related to ADS.

Data for Automated Vehicle Integration

USDOT launched Data for Automated Vehicle Integration⁶ (DAVI), shown in Figure 3, as an initiative to identify, prioritize, monitor, and address data exchange needs for AV integration across the modes of transportation. Access to data is a critical enabler of safe, efficient, and accessible integration of AVs into the transportation system. Lack of access to data could impede AV integration and delay safe introduction.

Source: USDOT

Figure 3. Illustration. Framework of Data for Automated Vehicle Integration.⁷

The USDOT DAVI framework provides a common language for identifying and prioritizing data exchange needs across traditional silos. It is designed to help stakeholders working on diverse aspects of AV integration understand each other’s data needs and learn from successful exchanges as they emerge. The framework defines key categories, goals, participants, and priorities of data exchanges identified by the department’s stakeholders, such as work zone data needed for AVs to navigate safely. USDOT continues to refine and update the framework based on stakeholder inputs.

In December 2017, USDOT hosted the Roundtable on Data for Automated Vehicle Safety to discuss potential priorities for voluntary data exchanges to accelerate safe AV integration. The department kicked off the Work Zone Data Exchange⁸ (WZDx) project in March 2018 to take on one of the priorities identified at the roundtable. The summary notes also call for enhanced inventories for roadways, which include high-definition maps already being developed. Developing inventories of fixed objects on the road, such as traffic signs, is not a difficult task and it has been done for many locations by private sectors. The rules behind the infrastructure (i.e., traffic laws and regulations) also need to be part of the map. Unfortunately, no complete digital database exists that addresses this key issue.

Work Zone Data Exchange and Initiative

Up-to-date information about dynamic road conditions, such as construction events, can help ADS and humans navigate safely and efficiently. Many infrastructure owner-operators (IOO) maintain data on work zone activity. However, a lack of common data standards and convening mechanisms makes it difficult and costly for third parties—including original equipment manufacturers (OEM) and navigation applications—to access and use these data across various jurisdictions.

The purpose of FHWA’s Work Zone Data Initiative (WZDI) is to develop a model practice for managing work zone activity data (WZAD) and to create a consistent language, through the development of a data dictionary and supporting implementation documents, for communicating work zone activity information across jurisdictional and organizational boundaries. The effort promotes a stakeholder- and systems-driven perspective for WZAD that serves the emerging need for improved real-time road condition information as well as traditional operations management, which benefits from improved data portability throughout project life cycles. This initiative seeks a shared approach to managing WZAD to benefit the broad spectrum of potential uses and users, acknowledging ADS as one of the key use categories.

Implementation of this language is occurring through the USDOT Intelligent Transportation System Joint Program Office’s (ITS–JPO) WZDx. The WZDx is a publicly available basic work zone data specification⁹ intended to jump-start voluntary adoption of a common data language by data producers and users across the country. By using WZDI guidance to determine agency-specific needs and uses for work zone data, and subsequently developing a customized specification using the WZDx as a foundation, there will be standardization for data sharing across organizational and geographical boundaries.

The WZDx specification enables IOOs to make harmonized work zone data available for thirdparty use. The intent is to make travel on public roads safer and more efficient through ubiquitous access to WZAD. Specifically, the project aims to get data on work zones into vehicles to help ADS and human drivers navigate more safely.

The WZDx working group is working to describe a set of common core data concepts, meanings, and enumerations to standardize a data feed specification to be used to publish work zone information. Common core is defined in this context as data elements needed for most (if not all) work zone data use cases that could possibly be defined. The data specification includes data elements that data producers (i.e., State transportation agencies and other IOOs) are already producing (required) as well as those not currently produced (optional). This common core is also considered extensible, meaning both required and optional data elements can be added to support specific use cases now and in the future.

The WZDx data feed will be incrementally enhanced to evolve into a data feed that supports advanced warnings to AVs in and around work zones. The current version (WZDx v1.1) is a first step in this effort and highlights common core elements that serve as a foundation for required data for effective data exchange This version addresses data currently supported by existing data feeds published by public and private-sector organizations.

WZDx data producers will use the specification to make their active work zone data feeds available to non-government users. These users may then use the harmonized data in a meaningful way, which will result in establishing the voluntary data exchange of work zone data. This approach is intended to be repeatable, leading to accelerated harmonization of local data.

Overview of Traffic Laws and Regulations

For constitutional and historical reasons, traffic regulations in the United States are enacted and administered by the States rather than the Federal government. The first statewide traffic regulations were enacted in Connecticut in 1901,¹⁰ before automobiles were common on roadways. Other States enacted their own regulations as need and custom dictated. The first version of the Uniform Vehicle Code (UVC) appeared in 1926.¹¹ The first Manual on Uniform Traffic Control Devices (MUTCD) was compiled by the American Association of State Highway Officials (AASHTO) in 1935.¹² In 1966, USDOT was established.

Although not directly responsible for traffic regulation, USDOT nonetheless oversees the safety of the nation’s roadways. As described in the 2013 Moving Ahead for Progress in the 21st Century Act (MAP–21),¹³ the Secretary of USDOT, under Chapter 4 of Title 23 of the United States Code , “Is authorized and directed to assist and cooperate with other Federal departments and agencies, State and local governments, private industry, and other interested parties, to increase highway safety.”¹⁴ This authority is then exercised through the department’s review and approval of the States’ highway safety programs. The National Highway Transportation Safety Administration (NHTSA) and FHWA Office of Safety administer highway safety programs within USDOT.

Most aspects of the national body of traffic regulations are consistent as a result of historical practices, institutional collaborations, and modern Federal oversight. The UVC¹⁵ represents a working consensus, though it has no formal standing as a body of law and has not been updated since 2000. As a starting point for this analysis, however, the UVC provides a common reference for the definition of terms used in framing traffic regulations and the user categories to which the regulations apply. The structure of the UVC has also been echoed in many of the States’ traffic codes, forming a de facto standard for indexing of the regulations. Similarly, the UVC and State traffic codes generally point to the MUTCD, or the State’s version, for the definition of particular traffic controls with which to be comply.

The advent of AVs creates multiple challenges for traffic regulations. Much of the body of traffic safety regulation concerns licensure of vehicles and drivers, and not specifically their behaviors. In the broadest sense, however, AVs blur the distinction between driver and vehicle, since driving automation systems reside in the vehicle and depend on its sensors. Recent regulation of AVs views AVs as a hybrid of vehicles and drivers, and is largely limited to their licensure for ODDs in particular jurisdictions under the presumption that existing regulations on driver behavior will remain applicable.

Existing Traffic Laws and Traffic Regulation Databases

The body of traffic laws across the United States varies from State to State and among local jurisdictions within those States. Reviewing existing traffic laws and traffic regulation databases, therefore, requires consideration of Compilation, State, and local perspectives.

Compilation Perspective

Since there are no national statutes requiring conformance to a single standard, and consequently no normative statutes, there have been various other efforts to document the actual diversity of traffic laws across the country. Particular perspectives and use cases for the resulting traffic regulation compilation or database have driven each effort.

Justia provides compilations of laws, codes, and statutes at the Federal and State levels, implicitly including traffic regulations. It appears to have been built as a portal for linking individual legal research to legal counsel. It does not address local government codes. It is primarily a set of links to documents in portable document format (PDF) and Hypertext Markup Language (HTML) format. For example: https://law.justia.com/codes/kansas/2018/chapter-8/article-15/.¹⁶

The American Automobile Association (AAA) Digest of Motor Laws¹⁷ provides summaries of traffic laws within individual States and across the country. It categorizes traffic laws, largely along the outline of the UVC, to list summaries of relevant laws across the nation. It also provides the same summaries for all categories within a particular State. It is not a complete representation of the traffic codes and does not link to the text of the actual statutes and codes. It does not address local variability within States. https://drivinglaws.aaa.com/.¹⁸

The National Council of State Legislatures (NCSL) maintains a database of current legislation relating to traffic safety. It provides a view of the delineation of existing laws, the impacts of emerging technologies, and changes in public policy. It links to, but does not directly provide, the underlying and enacted bodies of traffic regulations.

http://www.ncsl.org/research/transportation/state-traffic-safety-legislationdatabase.aspx#keywords.¹⁹

http://www.ncsl.org/aboutus/ncslservice/state-legislative-websites-directory.aspx.²⁰

NCSL also provides a database of legislation directly related to AVs.

http://www.ncsl.org/research/transportation/autonomous-vehicles-self-driving-vehiclesenacted-legislation.aspx.²¹

The National District Attorneys Association (NDAA) maintains a National Traffic Laws Center to provide support to district attorneys in enforcement of traffic law. It does not specifically provide a database of laws.

https://ndaa.org/programs/ntlc/.²²

The FindLaw website operated by Thomson Reuters provides summaries and links for some State traffic laws. It appears to be intended for individual research on traffic law enforcement and penalties for traffic law violations. It does not specifically provide a database of laws.

https://traffic.findlaw.com/traffic-tickets/state-traffic-laws.html.²³

The American Road and Transportation Builders Association (ARTBA) maintains a National Work Zone Safety Information Clearinghouse²⁴ of links to work zone safety laws across States and territories. In many cases the website provides direct links to State laws, but notes in a disclaimer at the bottom of the web page that links are for information only and does not necessarily include all relevant statutes.

https://www.workzonesafety.org/data-resources/laws-regulations-and-standards/statework-zone-laws/.²⁵

State Perspectives

State vehicle and traffic regulations are, in all cases, within the authority of the State legislatures. Execution and enforcement of those laws reside with the State motor vehicle administration, transportation, and police/patrol agencies, which may be separate or combined in various ways. Publishing the enacted vehicle and traffic statutes is a legislative function. State transportation agencies are as much users of those statutes as drivers within those States.

Although traffic laws across the United States are largely consistent and, in many cases, based on the UVC, available publications and databases of State traffic laws vary in structure, format, and wording. Electronic access to State traffic laws ranges from PDFs of entire sections of the statutes to searchable records of individual statutes. A detailed compilation of references to State statutes is provided in Table 2 of the Detailed Analysis of ADS-Deployment Readiness of the Existing Traffic Laws and Regulations.²⁶

The MUTCD provides another layer of consistency in traffic control deployments that complements the influence of the UVC. The State traffic codes prescribe that the State must have a standard for uniform traffic control and that drivers must obey the instructions of any official traffic control device. FHWA maintains an informational web page on the status of the States’ traffic control device specifications at https://mutcd.fhwa.dot.gov/resources/state_info/index.htm.²⁷

Some States may provide detail beyond the State traffic code with databases of information on deployed traffic control. For example, Ohio provides records of permits to local agencies for traffic controls such as speed zones, traffic signals, and signs on State routes.²⁸ However, no national databases of traffic control deployments exist.

Local Perspectives

Vehicle and traffic laws may be subject to additional local regulation where allowed (or not disallowed) by State authority. These local authorities may include counties, parishes, cities, villages, townships, or other such entities as identified in the respective States. The number and diversity of such local authorities and their transportation agencies preclude cataloging their traffic regulations databases for this analysis, other than anecdotally.

In general, the local regulations reference the State laws with which the local law conforms. Where allowed, local regulations may modify or take exception to the State traffic regulations. The City of Overland Park, Kansas, for example, provides its municipal code online at http://online.encodeplus.com/regs/overlandpark-ks/index.aspx.²⁹ The code is searchable by keyword or browsable by section. Title 12 of that code contains traffic regulations. Exceptions to the State code would generally be described as such. For example, Section 12.04.011 states, “All traffic control devices shall conform to the manual and specifications as adopted by the State department of transportation with the exception of handicapped parking signs as defined in 12.04.087”³⁰ [italics added for emphasis]. Extensions to the referenced State regulations may not be noted as such. For example, in its traffic control signal legend, Overland Park includes a flashing yellow arrow indication, even though such an indication is not part of the code for the State of Kansas.