Talking with Offer Grembek, Transportation Researcher, about Safe Systems & Speed

by Jenn Fox | July 4, 2020 | in News, People Behind the Progress, Safety Over Speed

Offer Grembeck speaking at the annual Transportation Research Board conference in D.C.

For this month’s People Behind the Progress, we’re talking with Dr. Offer Grembek, about modernizing speed setting practices and monitoring the frequency and types of crashes during the COVID-19 pandemic. Offer is the co-director of the University of California Berkeley Safe Transportation Research and Education Center and co-chairs the Transportation Research Board Global Road Safety Subcommittee.

Vision Zero Network: Thanks for your leadership on Safe Systems, which is fundamental to Vision Zero. What should we, as transportation professionals, community advocates, and others working for public health and safety, know about how Safe Systems relates to Vision Zero? Can you share a few specific examples?

Offer Grembek: Severe and fatal injuries are catastrophic outcomes of a system failure. A Safe System approach describes all the elements that are needed to build a transportation system that can prevent these catastrophic outcomes. In other words, it helps us build a transportation system where no road users can be severely or fatally injured.

To accomplish this, it is necessary to establish safety buffers that are large enough to contain hazardous situations. We are still committed to encouraging people to behave safely, but we recognize that things might go wrong, and we want the ‘system’ to be prepared for that.

It is a bit like designing a computer program that will not crash even if the user does something unexpected. Traditionally, our roads are considered safe as long as things go as planned, but with a Safe System approach, we plan for a much wider set of scenarios and users. So, if we revisit the computer analogy, we want to move away from blaming the user when a computer crashes and put more pressure on the system designer to make sure there is enough room to contain unexpected situations.

These safety buffers should be redundantly weaved through the components of the system which include roadway design and operations, vehicle design, policies to encourage safe road user behavior, and post-crash rescue procedures. This way, if a road user does not recognize a hazard, a technological system in a vehicle or infrastructure might spot it, and if not, there will be enough space to make an evasive maneuver. If the evasive maneuver fails, the design of the vehicle and the road can help reduce the impact and the people on the road an survive.

VZN: You participated recently in California’s Zero Traffic Fatalities Task Force, which developed this Report with strong recommendations for state-led policy changes to manage speed for safety. One of the recommendations is to modernize speed setting practices, by improving on  the 85th percentile approach, which is increasingly criticized for being outdated and adverse to safety goals. As someone who has researched this topic, how would you summarize the current approach to setting speed limits in California (and other places) and the potential for improvement?

OG: Speed is a core consideration when we are talking about safety since it determines the amount of kinetic energy that is carried by a moving vehicle, and to some extent the magnitude of the problem at hand. The opportunity to control or contain the energy is greatly diminished at higher speeds. This can affect a driver’s opportunity to respond to an emergency, and if a crash occurs, it can exceed the human body’s own protective capacity.

When we set speed limits using the 85th percentile approach, we set the limit to the speed at which 85 percent of the drivers are driving at or under. This is a bit like using the number of daily calories consumed by some Americans to set the recommended maximum calorie intake. It assumes that people can determine food intake by balancing their level of activity and nutritional needs. The reality is that people are more likely to eat more than what is needed, and if you use that to periodically set the bar it will increase over time even if the physiological needs did not change.

We have the same problem in speed setting since drivers tend to underestimate their speed, and do not believe that traveling at excessive speed threatens safety. It is also hard for drivers to assess the threat it poses to vulnerable road users. So instead of following the drivers’ actions to set speed limits, we want to make sure the speed limit is aligned with the safety standard of the road and vehicles, considering the mix of road users. For example, if a road has many people walking and biking, the speed limit should be set to the maximum speed that the vehicle and road design can protect users from death and serious injuries.

VZN: We saw that the Center you lead – the Safe Transportation Research and Education Center (SafeTREC) – launched this site which provides weekly updates of police-reported injury crashes on state roads (highways and arterials) in California. What can we learn about traffic safety opportunities and challenges based on the changes we are seeing with shelter in place?

OG: We developed this in response to the COVID-19 pandemic. The initial descriptive analysis of the data reveals that there is a noticeable reduction in injury crashes along state roads in California, which is good. However, it also shows that the reduction in fatal and severe crashes is smaller than the reduction in lower-level injuries. This means that injury crashes that do occur along state highways in California are more severe. We still don’t know whether this is due to worse driver behavior and willingness to take more risks (e.g., a lot more excessive speeding), or due to fewer congestion-related injury crashes which usually involve minor injuries. We are doing more research to better understand what is happening.

VZN: Your Center works regularly with the State of California – from geocoding traffic crashes to administering community safety workshops. And your coordination with the national Collaborative Sciences Center for Road Safety (CSRCS) means you are seeing examples from around the country. What traffic safety efforts in California are good models for others around the country? And what about other state efforts – is anything catching your attention as particularly noteworthy related to Vision Zero efforts?

OG: California is re-evaluating and refreshing safety programs across the state and conducting a multi-year effort to establish state-wide pedestrian and bicycle safety monitoring programs. Successful safety monitoring utilizes spot, corridor, and systemic methods to identify safety concerns and can be coupled with statewide pedestrian and bicycle exposure models to support safety analysis and resource allocation. Through our CSCRS involvement, we have been able to seed some insights and tools that are transferable to many other states. Some examples are a clearinghouse for bicyclist and pedestrian safety-related data and an enhanced systemic approach.

In general, I think that DOTs should try to use their partnerships with local universities to develop and implement safety programs that are derived from national practices but are customized to the needs and capabilities of the state. The overarching principles are transferable, but the actual applications must be specific to the state. My advice is to do a good survey of existing practices, but to piece it together in a way that makes sense for your state.


Thank you for sharing a small window into your work, including this impressive list of publications about Safe Systems, transportation modeling approaches, underreporting of pedestrian crashes, and more.

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