If you ask the question “How do we achieve transportation safety?” of a dozen individuals who work in or use the transportation system, you will probably get at least a dozen different answers. A policymaker will tell you it is through Vision Zero. An engineer will probably tell you it is through road safety audits. A planner may tell you it is through a “safe systems approach” focusing on vulnerable users over vehicles. A driver will likely be most concerned with getting from point A to point B as quickly as possible and mention that they are not the problem; other drivers need to pay attention. Are any of these individuals, correct? Are any of these individuals incorrect?
The idea of transportation safety is found in the reciprocal concept of risk. When we are 1% at risk, we are no longer 100% safe, and by entering the transportation system, we are inherently at risk. The latest National Highway Transportation Safety Administration (NHTSA) statistics indicate that in 2021 nearly 43,000 people died in crashes. The risk of death is ever-present. The number of people for whom a collision is not fatal, but remains life-altering, is far higher. NHTSA also estimated the cost of all crashes in the US in 2019 to exceed $340 billion. So, back to our dozen individuals. None of them are wrong, but they only see a small part of the picture for achieving safety. Every action to make any single part of the system safer is a success, so they are all also correct.
Our policymaker indicated that Vision Zero was the solution to transportation safety issues. The concept of Vision Zero is not a solution but multiple goals to advance transportation safety. The Vision Zero Network defines it as “a strategy to eliminate all traffic fatalities and severe injuries while increasing safe, healthy, equitable mobility for all.” So, Vision Zero is a goal; under that comes the hard part of finding ways to achieve the goal and getting all the involved parties to agree and do their roles. Our planner indicated a “safe systems approach,” like Vision Zero Network’s definition. The FHWA has directly connected the safe systems approach to its Vision Zero strategy to drive understanding of the goal better. An FHWA brochure provides six guiding principles:
The reframing of the approach to safety is also essential. Instead of trying to make a roadway system where no crashes occur, the goal instead is now to create a system (including designers of vehicles and first responders to the crashes) where no collision results in a fatality or severe injury. The system in focus is now much larger, and the spread of responsibility is much greater. So how does this happen? The Safe System Approach does better identify those who can make a change, but it still does not get to the level of acting to identify problems.
(Source: FHWA brochure, “The Safe System”)
Our engineer indicated that road safety audits were the solution. The road safety audit was the gold standard for making a roadway segment safer for many years. This process is still incredibly effective and remains valuable in the quest for safer roads. The US Federal Highway Administration (FHWA) defines a road safety audit (RSA) as “the formal safety performance examination of an existing or future road or intersection by an independent, multidisciplinary team. It qualitatively estimates and reports on potential road safety issues and identifies opportunities for improvements in safety for all road users.” This process is detailed, time-consuming, and costly from start to finish as it involves a team of professionals that must coordinate. For many safety concerns, this may be far more than necessary.
Fortunately, there are alternatives to the formal road safety audit. If there is a need for that level of detail, finding and coordinating an entire RSA team to travel to the site to perform the audit is no longer necessary. The Traffic Operations and Safety Laboratory at the University of Wisconsin developed and deployed a process known as a Virtual Road Safety Audit. This method allows for the use of a driving simulator to instead examine the roadway in a simulated (converted) environment to eliminate the need for (at least) some elements of the on-site examination.
There are other alternatives to the RSA or Virtual RSA, however, and these can be deployed proactively or reactively, just like the audit process. For example, most communities have a pretty good idea of which intersections or roadway segments are the most hazardous. This information can be gleaned from crash records, first responder calls, or even a question posted to a city “gossip” Facebook page (this third option may get the information the fastest, truthfully). From that information, an engineering firm can be hired to do a small, focused study that gathers crash reports, roadway/intersection design features, traffic volumes, etc. These types of proxy data may be great for showing risk potential and resultant outcomes, but they still need to show the entire picture. It is just as possible that a location commonly known in a community as hazardous will have low volumes and almost no crashes. In a case such as this, the (reactive) proxy data fails to show any actual problem. This is where a trained road safety professional with a background in engineering design is needed. An engineer with experience in traffic engineering, focusing on safety and human factors (behaviors), can delve deeper and identify specific issues that the proxy data may not show that explain the entire picture.
It is also possible, however, that a community has not had the time or energy to identify their problem intersections continually, or there is some concern that only a few busy intersections often get all the attention to the detriment of other, possibly more dangerous, locations. So how can a city reframe the goal to a more “safe systems” approach?
The shift in focus does require taking a more holistic view. Rather than starting with a single intersection or roadway segment, it is necessary to take the so-called “thirty-thousand-foot view” and compile systemwide records of crashes, traffic volumes, and geometrics. From this expansive view, a formal advanced statistical modeling process can be implemented. Commonly a modeler would employ a methodology like Empirical Bayes that is designed to compare actual and expected outcomes while holding a baseline against variable alternatives. A process like this, where each intersection in an entire city is compared to the expected baseline “average intersection,” can most effectively identify intersections that are actual outliers in terms of safety, not just those with the most crashes (which are often also just the busiest intersections).
A modeling process like this can also be fine-tuned to put additional emphasis (or weight) on specific items of concern, such as crashes involving pedestrians or bicyclists, rather than just motorized vehicles. This also shows the strength of a formal approach; it can identify features and issues that otherwise would be lost in a sea of data. The resultant outcome of the statistical modeling process is a score for each intersection based on how far it deviates from the expected baseline. This allows for rank ordering the list of intersections, which provides a community with knowledge of the intersections that need the most attention and allows for hiring that road safety professional engineer to do a deep dive into the worst intersections to develop solutions (specific countermeasures to implement) unique to each location.
Ultimately, transportation safety is not achieved by a single idea, policy, program, or type of activity. The framework provided by a safe systems approach, using the goals of Vision Zero, gives a starting point and a target to aim for. Employing an evaluation process like road safety audits enables the implementation of that framework by identifying safety issues to resolve through countermeasures. Moving beyond the idea that road safety audits are the only option allows for a far quicker response to problems that have been identified. The inclusion of a statistical modeling approach that holistically evaluates an entire network of intersections to identify the most hazardous locations allows for achieving the “greatest bang for the buck” with limited safety funds. Combining these different approaches is the best way to move forward, making the system safer, one intersection at a time.
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