US NHTSA is Defining Safety for Self-Driving Cars

Article By : Egil Juliussen

U.S. NHTSA has made a good effort in researching and proposing its ADS safety framework under trying circumstances. The Autonomous Vehicles industry is now asked to answer 25 questions to add their expertise...

Editor’s Note: The National Highway Traffic Safety Administration (NHTSA), an agency of the Department of Transportation (DoT) of the USA, released last November its advance notice of proposed rulemaking (ANPRM) for autonomous vehicles. We asked Egil Juliussen, a veteran automotive industry analyst and EE Times’ resident columnist (“Egil’s Eye”), to break it down for us. In the following article, he spells out how NHTSA defines autonomous vehicles, what the agency has included in its “safety framework,” and what questions NHTSA wants the AV industry to answer to improve its ANPRM.

On November 19, 2020, U.S. NHTSA released its advance notice of proposed rulemaking (ANPRM) for autonomous vehicles. Written comments are due by February 1, 2021. This is the beginning of the process of creating rules that will dictate how autonomous vehicles should perform. These will be some of the most important guidelines for the entire vehicle industry for years to come. What is NHTSA looking for, and what might we expect to come out of this process?

The name of the ANPRM is “Framework for Automated Driving System Safety.” The official version of the 60+ page document was included in the Federal Register on December 3, 2020 (an 18-page section in small print). There is also a link where public comments can be read; comments can be filed here.

To describe autonomous vehicle hardware and software, NHTSA is using the terminology, “Automated Driving System (ADS).” I will also use “ADS” instead of autonomous vehicle (AV) in the rest of this column.

The next paragraph is the summary of ADS ANPRM by NHTSA.

NHTSA is requesting comment on the development of a framework for Automated Driving System (ADS) safety. The framework would objectively define, assess, and manage the safety of ADS performance while ensuring the needed flexibility to enable further innovation. The Agency is seeking to draw upon existing Federal and non-Federal foundational efforts and tools in structuring the framework as ADS continue to develop. NHTSA seeks specific feedback on key components that can meet the need for motor vehicle safety while enabling innovative designs, in a manner consistent with agency authorities.

Written comments are due by February 1, 2021 to the Federal eRulemaking Portal: Comments must refer to docket number: NHTSA-2020-0106

When NHTSA have made standards or updated regulations via its ANPRM procedures, it has lots of data and statistics on the topics. NHTSA’s first Federal Motor Vehicle Safety Standards (FMVSS) came after the Safety Act was passed in 1966. Even then, NHTSA had lots of crash statistics that could be used to determine what type of FMVSS regulation was needed to lower crash rates. Today there is much more crash data, but very little that can help develop ADAS features and other safety systems.

Developing a FMVSS for ADS is much harder due to multiple issues:

  • There no ADS vehicles that NHTSA can test and learn from.
  • There is no operational data from ADS usage that NHTSA can analyze for FMVSS safety framework.
  • ADS technology is advancing rapidly and may make safety regulation outdated in a decade or so.
  • NHTSA does not have enough technical expertise to develop an ADS safety framework by itself.

NHTSA’s Challenges
As the old saying goes, NHTSA is essentially “between a rock and a hard place”. There is already criticism that this NHTSA’s ANPRM publication is too weak, too friendly to the auto industry and does not have enough technical content and safety rules.

Some of this critique may be valid, but it does not consider the constraints that NHTSA has been working under — budgets, technical resources and political issues.

Essentially, NHTSA has to get cooperation from the ADS industry because that is where the technical expertise resides and will continue to grow as ADS technology advances at a rapid pace for multiple ODD and use-cases. Hence NHTSA is on the right track for developing an ADS framework and future FMVSS by working with the ADS industry.

NHTSA ADS Framework Approach
NHTSA has been working on autonomous technology and has released multiple ADS-related publications. Most ADS publications have focused on which requirements of the existing FMVSS are relevant to the safety of ADS-equipped vehicles without manual driver controls. NHTSA is  also adapting and developing the requirements for test procedures that can be applied to ADS vehicle designs without adversely affecting safety.

NHTSA ADS Definition
An ADS is the hardware and software that are, collectively, capable of performing the entire dynamic driving task on a sustained basis, regardless of whether it is limited to a specific operational design domain (ODD).

In less technical terms, an ADS maintains the control and driving functions within the situations that the system is designed to operate in.

What is included in the ADS Framework?
NHTSA’s ADS ANPRM is a complex document with 64 pages of information on regulation constraints, technical details, perspectives of what has worked and not worked in the past plus lots of discussion on how this will impact ADS framework and future FMVSS regulation. NHTSA is very concerned about the impact of technology advance and future innovation and does not want to impede future advances.

The next figure is a big picture of what is included in the NHTSA ADS Safety Framework. NHTSA is relying on research and expertise from the ADS industry (automotive and high-tech). The left side of the figure lists NHTSA’s activities (in black) with the right side, showing ADS industry contributions (in blue). The red block in the middle is the future ADS Safety Framework.

Click the above to enlarge. (Source: Egil Juliussen)

The blocks in the above figure corresponds to NHTSA’s major content segments in the ANPRM document. There are basically two main segments—technology for the ADS framework and administrative mechanisms for ADS implementation and oversight. The two categories have several categories that are shown in the above figure:

  • NHTSA engineering measurement: prior research and reports
  • ADS Industry engineering measurement: Core autonomous technologies
  • ADS Industry engineering measurement: Proposed ADS frameworks
  • ADS Industry process measurement (standards)
  • Administrative mechanisms: Regulation mechanisms
  • Administrative mechanisms: Voluntary mechanisms for ADS industry

NHTSA wants input from the ADS industry and included 25 questions for comments. The deadline for comments is February 1, 2021. I have included perspectives of the blocks in the figure below.

NHTSA Engineering Measures
NHTSA has done lots of research to prepare for developing an ADS safety framework. It has released four primary AV guidance reports:

  • AV 1.0: Accelerating the Next Revolution in Roadway Safety (September 2016)
  • AV 2.0: A Vision for Safety (September 2017).
  • AV 3.0: Preparing for the Future of Transportation (October 2018).
  • AV 4.0: Ensuring American Leadership in Automated Vehicle Technologies (January 2020).

NHTSA launched its Automated Vehicles Transparency and Engagement for Safe Testing (AV Test) Initiative to provide information on ADS development. This website (AV TEST Initiative | Automated Vehicle Tracking Tool | NHTSA) is an interactive tracking tool to see who is doing ADS testing and where.

NHTSA launched AV Test in June 2020 with states, local governments and private ADS stakeholders. The website provides the public with ADS information from states regarding activity, legislation, regulations, local involvement in ADS activities, and information from companies developing and testing ADS.

NHTSA’s research focuses on ADS safety performance, and seeks to identify the methods, metrics, and tools to assess how well ADS vehicles perform. Such assessments include system performance and behavior relative to the system’s stated ODD and object and event detection and response (OEDR) capabilities, as well as fail-safe capabilities if/when it is confronted with conditions outside its ODD.

NHTSA has developed multiple ADS safety performance models and metrics. The Instantaneous Safety Metric (ISM) calculates physically possible trajectories that a subject vehicle and other roadway users in the surrounding traffic could take given a set of possible actions. The Model Predictive Instantaneous Safety Metric (MPrISM) is an updated approach that builds upon the ISM concept and modifies its assessment method.

ADS Industry engineering measurement: Core technologies
ADS vehicles must perform the driving functions that drivers perform—sense all road actors, perceive or understand what road actors are doing, plan the driving path and control the driving direction, speed and stopping. Much ADS research is focusing on finding the right solutions to these core ADS functions.

ADS Industry engineering measurement: Proposed ADS frameworks
NHTSA discussed three proposed ADS frameworks from the ADS industry. Mobileye proposed a framework called Responsibility Sensitive Safety. RSS is a mathematical model for multi-agent safety that incorporates common-sense rules of driving while interacting with other road users to minimizes the chance of causing a crash, all while operating within normal behavioral expectations.

Nvidia proposed another framework called the Safety Force Field that use a computational method to assess through simulation whether an ADS is monitoring its surrounding environment successfully and not taking unacceptable actions.

Rand released a report in 2018 that proposed a safety framework that considered how to define and how to measure ADS safety.

ADS Industry process measurement (standards)
ISO 26262 describes a process for the evaluation of functional safety to assist in the development of safety-related electrical and/or electronic systems. It is a core standard for ADAS functions and future ADS systems.

ISO 21448 or Safety of the Intended Functionality (SOTIF) is intended to be applied to functions where proper situational awareness is critical to safety, and where that situational awareness is derived from complex sensors and processing algorithms; especially emergency intervention systems. SOTIF does not apply to faults covered by the ISO 26262.

UL 4600 is a process focused standard that is intended for use by the manufacturers in developing ADS. UL 4600 was developed primarily for ADS.

Administrative mechanisms: Voluntary mechanisms for ADS industry
NHTSA’s AV 2.0 publication introduced the concept of a Voluntary Safety Self-Assessment (VSSA). This document identified 12 safety elements that ADS developers should consider when developing and testing their technologies. 26 companies have filed their VSSA report as of January 14, 2021. See: Voluntary Safety Self-Assessment | NHTSA

NCAP has grown in importance and is being used for ADAS functionality. It makes sense to add an ADS competency evaluation in future NCAP updates. This could be a FMVSS obstacle-course performance test that would be useful consumer information under the NCAP program.

Currently, ADS technology development remains uncertain and will see many future advances and innovations. Hence, the appropriate regulatory performance metrics and safety thresholds remain unknown. NHTSA has therefore sought to enhance safety through voluntary guidance, instead of mandatory requirements.

Administrative mechanisms: Regulation mechanisms
NHTSA has already taken steps to require the disclosure and reporting of certain information when exemptions to current FMVSS are given. Nuro’s exemption to deploy goods ADS is an example.

NHTSA has broad jurisdiction over motor vehicle safety, with a purpose to “reduce traffic accidents and deaths and injuries resulting from traffic accidents.” NHTSA believes that, at some point, regulation of the ADS will likely be necessary and is exploring ways to regulate ADS. NHTSA could create new FMVSS regulation or modify existing FMVSS regulation for ADS vehicles.

NHTSA has typically used its FMVSS authority in two ways:

  • Either to mandate the installation of a proven technology by way of performance standards to address a safety need and subject the technology to minimum performance requirements.
  • Or to regulate voluntarily installed technology by subjecting the technology to minimum performance safety requirements.

NHTSA is also considering a new way of developing FMVSS regulation due to the rapid technology changes from the software-defined car and remote software updates. A new generation of FMVSS should give the manufacturers of vehicles, sensors, software, and other technologies needed for ADS sufficient flexibility to change and improve without the need for frequent modifications to the regulations.

NHTSA Questions to ADS Industry
NHTSA wants strong participation from the ADS industry and has a list of 25 questions to the ADS industry. The deadline for making comments to the ADS ANPRM is February 1, 2021. As of January 14, there was 16 comments. One comment from CTA (CES 2021 organizer) asked for an extension to March 3, 2021. I was surprised to see that very few entries were useful. The ADS industry needs to make a better effort to add their expertise to the NHTSA’s ADS ANPRM!

Evolution of NHTSA ADS Safety Framework
The next figure is an attempt to put this in perspectives and make some projections on where NHTSA’s ADS framework may be going. A few of the blocks from the previous figure are included on the left with future projections shown in red. There are lots of questions listed in the red blocks and in green.

Click the image above to enlarge. (Source: Egil Juliussen)

A big question is whether ADS framework will be needed for the key ADS use-cases such as autonomous truck, robotaxi, goods ADS and eventually consumer ADS. And if these ADS framework for use-cases will evolve in FMVSS regulations. I think that is likely as shown in the above figure. After Mobileys’s CES 2021 presentation (Why Consumer AV in 2025 Is ‘Believable’ | EE Times), I added the consumer ADS to the figure, but only for L4 capability. L5 would be much later.

Another question is about the Self-Drive act passed by the House, but not by the Senate — what future impact will it have if/when passed?

In summary, I believe NHTSA has made a good effort in researching and proposing its ADS safety framework under trying circumstances. The ADS industry needs to answer the 25 questions and add their expertise to improving the ANPRM.

I will discuss NHTSA’s ANPRM for autonomous vehicles further in my next column, by going into more details.

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