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What is the importance of high-quality SOTIF functionality?

By Adam Saenz on Sep 13, 2022 10:21:16 AM

Topics: SOTIF

What is the importance of high-quality SOTIF functionality?


In the 3rd blog in this series, The SOTIF Scenarios, we reviewed the four SOTIF scenarios: Known Safe, Known Unsafe, Unknown Safe, and Unknown Unsafe. In this article, we return to the four scenarios, but with a quality-oriented mindset, focusing on the why and how of defining and achieving SOTIF scenarios of high quality in a manner that is measurable and repeatable.

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Determining what “Safe” is


Moving beyond just the absence of risk

Safety Of The Intended Functionality (SOTIF) is defined in ISO 21448:2022, “Road vehicles — Safety of the intended functionality”, as the absence of unreasonable risk due to hazards resulting from functional insufficiencies of the intended functionality or by reasonably foreseeable misuse by persons. The SOTIF process is used to assess the functionality of a system under almost any circumstance (a scenario), and define its safe state regardless of whether:

  • it is being utilized as intended,
  • it is being utilized in a manner that was not part of the original design intent, or
  • it is reacting to unforeseen circumstances either within the vehicle or out in the surrounding operational environment.

Okay, that defines the “what”. But what about the “how” and “why”?

For this level of safety to be achieved, the system needs to be capable of making the correct decisions, every time, swiftly and reliably. For the system to make those decisions, it needs:

  • accurate and complete data,
  • consistent data meanings,
  • the proper logic and computational capability to think, learn, and react accordingly,
  • actuators to accomplish useful physical work, and
  • some form of feedback and validation.

Let’s look at some of these considerations in further detail:

Accurate and complete data

At its most fundamental level, driving is an exercise in data transfer, and it has been since the very first moments of the automobile. Even in its earliest crude infancy, the act of driving was a chaotic tossed salad of data transfer and feedback loops between the environment, the cars, and the humans driving them. It may have been analog, but it was still data.

Without data, the act of driving, in any form, simply could not have happened. Human brains provided both computational power and actuator control. The human senses served as the early system sensors, eventually augmented with gauges and other instrumentation. Drivers took the data the environment provided… visual cues, temperature, wind, rain, road conditions, light levels, smells, audio cues in the form of engine noises, and even the vibration transferred to the human through the seats, floorboards, pedals, and steering wheel… and applied logic derived from knowledge earned through firsthand experience and shared from outside sources.

The driver used all these elements to make supposedly sound decisions about how to drive the car. However, the real-world results were often mixed. Sometimes they failed spectacularly, but on average it was typically a better overall experience than the conveyances that came before, and it generally beat walking. It was an imperfect improvement.

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Consistent data meanings

What drove subsequent improvements, was the need for a better and safer driving experience. But what enabled those improvements was improved data: accurate, complete, and consistent, which in turn enabled the design of safer vehicle systems. The more consistent the data got, the clearer the picture became as to what needed to be improved and why, which led to figuring out how to improve those systems, which in turn enabled the improvement and refinement of the driving experience.

For example, the earliest crude vehicles had no instrumentation. On some, the earliest onboard instrumentation was the addition of a temperature gauge built into an optional aftermarket radiator cap installed way out there on the front of the car. With the development and gradual improvement of instrumentation and it’s relocation to inside the car on a clustered dashboard control panel, precise data became available to the driver in real-time. Hunches and guesses about temperatures, speeds, and engine parameters became known data points displayed on gauges with trustworthy numbers that humans could act upon with greater confidence.

Instrumentation became standardized, at least so far as to what kind of information a driver could expect to find on the dashboard and the meaning of those numbers; speed in M.P.H. means the same thing no matter the vehicle or its instrumentation layout. And the items measured by engineers and mechanics became more consistent as well. Techniques were developed to consistently measure the precise stopping distance of a vehicle at a given speed and weight, which in turn led to the development of vehicles that were more stable and could brake faster and more controllably. Brighter and more effective headlights were developed in part by creating the means to measure both their brightness and the shape of their beam in a consistent and repeatable setting. Increased visibility became a mathematical function of area and viewing angles that were measurable in the same consistent way regardless of the vehicle’s shape; in turn, this data gained greater influence over the vehicle’s cabin design and ergonomics, rather than the artistic design aesthetics alone having precedence.

This foundational point about the importance of data consistency is easily overlooked. But it is an important point that draws a bold thread linking the earliest days of automotive technology to the most modern mechatronic vehicle systems. Consistency in data is a key measure of the quality of the data. True then, true now.

There is real value today in remembering the importance of quality data. Without ensuring that your data is accurate and complete, without the adoption of common data types and the universal acceptance of the meaning of those numbers, without broad consistency across the automotive spectrum, and without a trustworthy level of proven reliability in the data, safe driving would have remained a distant dream. Instead, the quality of the driving experience was defined and measured with real numbers, performance could be measured, and improvements implemented. The fundamental building blocks for today’s quality digital data systems and all modern safety efforts were forged in the analog data crucible of the very beginning of the automotive realm.

The limitations of human-based data processing

As time went by, data accuracy improved with the increased sensitivity and ruggedness of improved instrumentation, but the data were still being processed in real-time, by humans. This data was the product of imperfect processing and subjective storage in the form of scribbled notes and fallible human memory. It was limited as much by the bandwidth constraints of the human brain as by the technology.

The shortcomings in these systems revealed the need to improve them beyond flawed human idiosyncrasies. Better sensors and instrumentation were developed to transcend the humans in order to better serve them. Today, the typical modern vehicle is equipped with sensors, actuators, and computational power thousands of times more advanced than those that helped the space program put men on the moon. The quantity and complexity of the electronics and data now being utilized, and the ability to utilize them with greater effectiveness, has necessitated the creation of safety standards like SOTIF.

Twenty years ago, a safety standard like SOTIF was not needed because there was no data used outside of human intervention. Today, SOTIF processes break a problem down accurately and completely into its base elements to the point that it can’t be broken down further, to define and help achieve truly safe states. The quality of the data remains an important factor, which is why sensors of different technologies are utilized together to help mitigate the shortcomings of using each type individually.


Components, proper logic, and computational capability

It doesn’t do much good to create high-quality SOTIF scenarios if your system can’t leverage them to perform useful work. The system needs to know what questions to ask, when to ask them, and what the correct answers are supposed to be. In a modern vehicle, this knowledge is programmed into the system and locked in for production.

To perform this computational work, the system needs a huge volume of relevant data to feed upon, in addition to clear definitions of safety. The data must be accurate, timely, and complete. The data serve as the fundamental building blocks for defining “what is”. But it also defines what something is supposed to be. The difference between what something actually is, and what it is supposed to be, is analyzed by the system to prioritize issues and determine whether that condition is, at that moment, safe.

Key takeaways for defining and managing quality SOTIF scenarios

Now that we have explored some of the historical context that has driven forward the automotive safety efforts of today, and we better understand why quality data is important in creating SOTIF scenarios, we can explore what actually constitutes quality in the SOTIF scenarios themselves. Simplified, these considerations include:

  • A SOTIF scenario must be described in a manner that is accurate, complete, and unambiguous.
  • The very definition of “safe” in any given situation must be clarified. This is a binary determination. Either the state is safe, or it is not.

An examination of some of the key elements of the SOTIF standard help to reinforce these points.

The SOTIF-related hazardous event model

In ISO 21448:2022, Section 4.2.1, the SOTIF standard states:

“The main objective of this document is to describe the activities and rationale used to ensure that the risk level associated with all identified SOTIF-related hazardous events is sufficiently low.

“The function, system specification and design include relevant use cases which, in turn, comprises several scenarios. These scenarios could contain triggering conditions that lead to harm… In order to avoid the harm, proper situational awareness is necessary.”


Figure 4 — Visualisation of a SOTIF-related hazardous event model


Further study of this flowchart underscores the cause-and-effect nature of hazardous events. The causes and ramifications of hazardous events can vary wildly, but their structure is consistent. And it is in that consistency, that we find the first stable handle that we can grab onto in order to wring logic out of the event chaos.

A key takeaway from this model is also the importance that situational awareness plays in avoiding harm. This ties right back to the quality of the incoming data that we explored in the first half of this article. It is not enough to be aware; you must also be accurately aware.

The four scenario areas

In ISO 21448:2022, Section 4.2.2, the four types of scenarios are classified, as illustrated in Fig. 5:



The various approaches to, and nuances of, the evaluation of the four scenario categories, are covered in detail in the standard. But there are some key quality-related points worth revisiting:

  • Scenarios that are in area 4 (Unknown but Not Hazardous) do not impose the risk of harm.
  • Once a scenario in area 4 (Unknown but Not Hazardous) becomes known, it is moved to area 1 (Known but Not Hazardous). As the quality of awareness improves, the nature of the hazard remains unchanged.
  • The probability of scenarios in area 2 (Known and Hazardous) causing hazardous behavior, can be reduced to an acceptable level by raising the functionality to an appropriate level of quality.
  • An adequate verification and validation strategy can reduce the probability that the area 3 (Unknown and Hazardous) scenarios might cause potentially hazardous behavior.
  • A given use case can include both known and unknown scenarios.
  • Exploring the scenarios of each use case can lead to the identification of previously unknown scenarios.

Statistics-based testing plays a key role in keeping the SOTIF process practical. Remember, the ultimate goal of the SOTIF activities is to evaluate the potentially hazardous behavior present in areas 2 and 3 (the Hazardous areas) and to provide an argument that the residual risk caused by these scenarios is sufficiently low, i.e. at or below the acceptance criteria. For example, while the risk resulting from the known scenarios in area 2 (Known and Hazardous) must be explicitly evaluated, the risk resulting from unknown scenarios in area 3 (Unknown and Hazardous) has been determined by statistics-based testing to be sufficiently small. This helps to prevent the unnecessary expenditure of resources and effort.

The interaction of quality management, systems engineering, and functional safety

In order to develop a safe vehicle, rigorous engineering and quality management processes, applied with discipline and consistency, are essential.

Key steps in the SOTIF process that impact functionality

  1. The SOTIF process starts with defining the specification and design of the system and its architecture. After all, you can’t know if you have hit your target if the target is not yet defined.
  2. The intended functionality of the system is detailed.
  3. The potential hazards of the intended functionality are identified, and they are subjected to a hazard identification and risk evaluation process. The hazards are clearly identified, and their corresponding hazardous events are defined. (After an evaluation of the results, if it is determined that these hazardous events do not lead to an unreasonable risk of harm, then no additional design measures are applied.)

It is important to note here that the causes of hazardous behavior from the intended functionality are not considered, only their consequences for safety.

  1. The focus is to evaluate hazardous events that could result from hazardous behavior, and to define the acceptance criteria. SOTIF is not modified to conform to function. If it is deemed necessary because of these activities, the functionality is modified to improve the SOTIF.
  2. A verification and validation strategy is then developed to provide evidence that the remaining residual SOTIF-related vehicle-level risk now falls below an acceptable level, and that the components meet their functional requirements.

Afterward, corresponding verification and validation test cases can be derived to evaluate if the resulting risk is sufficiently small.

Distributed SOTIF development activities

High-quality SOTIF scenarios cannot be defined if the overall team is in disarray. As stated in ISO 21448:2022, Section 4.2.2,

“In case of a distributed product development, a development interface agreement (DIA) is defined between all involved parties. The goal of the DIA is to confirm, in the early stages of a project, all responsibilities of the SOTIF activities and that adequate technical information will be exchanged between the development parties.”

At this point, it is important for the DIA to be tailored to meet the unique requirements, capabilities, and expectations of the business entities involved. The process for doing so is detailed in the standard, but the importance of this work cannot be overstated. This is the document that will drive and shape all subsequent SOTIF work on the product, both figuratively, literally, and legally. A lot of time, effort, and resources will be allotted and predicated on what is detailed therein. Clarity and completeness, qualities whose importance has already been underscored elsewhere in this document, are especially important here.

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The automotive industry in general is still trying to wrap its arms around the challenge of finding the optimal way of integrating SOTIF organically into the design process from the start. The standards certainly help, but the task of integrating SOTIF can be eased somewhat by reinforcing the importance of quality data. The automotive realm has seen the consequences of allowing quality to slip. Quality data acted upon with discipline is the foundation upon which SOTIF success is built.


Interested in learning more about SOTIF for your organization? Contact our team today!




Further reading and references

What is SOTIF(Safety of the Intended Functionality) ISO/PAS 21448

What is the scope of SOTIF?

What are the SOTIF Scenarios 

Adam Saenz

Written by Adam Saenz

Adam joined LHP in 2018 bringing over 15 years of engineering experience in many areas of product lifecycle development. He specializes in embedded system design and has held positions as a software engineer, electrical engineer and systems engineer. As a software engineer, he has worked on control algorithm development and device driver level software. His hardware experience includes analog and digital circuit design, PCB layout, and FPGA firmware development. His system engineering experience includes developing architectures, writing requirements, and test case/procedure development and execution. Over the years, Adam has gained extensive experience in board bring up, hardware/software integration, and troubleshooting at the PCB, system and system-of-systems levels. He utilizes his experience in both hardware and software to determine the root causes of problems and apply the appropriate solution at the right level. Adam has also designed Automated Test Equipment (ATE) systems for verification and validation of safety-critical applications. His design approach utilizes as much off-the-shelf hardware as possible with a common software architecture to minimize costs and development time between projects. His ATE designs have been used in testing high input/output (I/O) products for military, aerospace, and industrial applications. Adam is a Functional Safety Certified Automotive Engineer (FSCAE) and has spent most of his career working on safety-critical projects. He has developed software for Aerospace DO178 Level A products, and hardware and FPGA designs for safety-critical products in the rail and industrial machine tooling industries. Adam attended California Polytechnic University Pomona and has a Bachelor’s of Science in Electrical and Computer Engineering. He also has an Embedded System Engineering Certificate from the University of Irvine.