Speeding up Technology Use for Setting Equitable Speed Limits

By John Lower

John Lower is a Fellow of the Institute of Transportation Engineers, a League of American Bicyclists certified instructor, and a 20-plus years City Transportation Manager practitioner now providing thought leadership with Iteris, Inc. in the areas of transportation and smart communities.

Oct 9, 2017 | Governance, Mobility | 1 comment


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A 55 year old hotel worker, Patrick Shannon, was struck by a speeding vehicle as he was bicycling home from his job at the Anaheim Marriott. He was found unconscious with severe head injuries and died six days later. This street violence happened in 2009, the same year that 18 year old Anaheim resident John Lee LaBord was bicycling home from his shoe store job and wound up being lodged into the broken windshield of a speeding car that continued to drive for another 13 miles before dumping the cyclists body.

These tragic events occurred the year that I became the City of Anaheim Transportation Manager. The cyclists are long dead, but the memories don’t die. These are regrettable examples of the 35,000 to 40,000 road deaths happening each year in the U.S. – and the numbers are rising.

Speed Kills

Despite the trend of more communities embracing the concept of smart cities, which can lead to vast improvements for in-car safety technology – from electronic stability control systems to rearview cameras and additional airbags – as well as improved road sensor technology, 2016 saw a 6% rise in road fatalities compared to the year before. This increase is higher for our most vulnerable road users: pedestrians and cyclists.

According to the National Transportation Safety Board (NTSB), speed-related crash deaths numbered 112,000 in the U.S. between 2005 and 2014 – an average of 10,000 deaths a year. Millions more crash survivors are left with life-altering injuries. Vision Zero produces an interactive map showing tragic accidents that could have been avoided with better speed limit laws.

How could these deaths have been avoided, or at least reduced?

Aside from the more broad-brush moves by jurisdictions to promote lower speed limits in the fight against rising traffic fatalities, I would argue that the logic underpinning how current speed limits are set is outdated and must change.

Setting the Pace

Speed limits are set by state and local agencies, typically following guidance from the Federal Highway Administration’s Manual on Uniform Traffic Control Devices. The most widely used speed-setting method in North America is called the engineering approach, whereby the speed at which 85 of 100 measured vehicles travel during uncongested times is the predominant factor used in establishing speed limits.

As I mentioned in my recent ITE Journal article on active transportation users setting safe speed limits, this base speed may be adjusted according to traffic and infrastructure conditions not readily apparent to the driver, such as high pedestrian or bicycle activity, but few if any jurisdictions have quantitative criteria for adjustments to the 85th percentile speed.

Old Habits Die Hard

The ludicrous thing about the 85th percentile approach, which has justifiably been described as laissez-faire, is based on 53-year-old research by David Solomon, whose 1964 study found that the risk of a vehicle collision increased at speeds above and below the mean speed of all traffic.

Despite Mr. Solomon’s study being confined to “main rural highways”, it is currently being applied across the U.S. for use in busy, urban street segments in dense and multimodal Smart Cities.

Calls for Change

Fortunately, leading up to the recent NTSB report, there has been a crescendo of calls for a change to the way speed limits are set:

  • The National Association of Transportation Officials 2017 Policy has called for state laws and rules that set speed limits at the 85th percentile to be repealed.
  • Vision Zero Network’s 2017 Moving from Vision to Action report prioritization to directly and assertively manage speeds on roadways by collecting, analyzing and using data to manage speed to safe levels.
  • California’s 2017 Toward an Active California State Bicycle and Pedestrian Plan’s strategy to research methods for setting and enforcing speed limits, other than the standard approach that now uses the 85th

The Alternative Mindset

At the core of the drive to propagate the idea of Smart Cities is a desire to harness data and gain insights to solve urban challenges. If sensors are collecting vehicle data only, the data will not speak to the volumes of pedestrians and bicyclists using the street network – the vulnerable road users (VRUs) that are essential to Smart Community initiatives to expand transportation options, reduce transportation congestion and environmental costs.

To accelerate the relationship between data and action, smart sensors can be deployed to collect data on the mode shares of trips made by VRUs. De-risking the urban street network should clearly begin by setting safer speed limits where there are higher mode shares of VRUs.

The Road Ahead

As the NTSB report highlights, speed is a deadly problem on our streets and roads, and we must do more to address it. The NTSB concludes that expert systems such as USLIMITS2 can improve the setting of speed limits by allowing traffic engineers to systematically incorporate crash statistics and other factors, including quantified pedestrian and cyclist mode shares, in addition to the 85th percentile speed.

The NTSB further recommends that the Federal Highway Administration revise the Manual on Uniform Traffic Control Devices so that factors currently listed as optional for all engineering studies are required, and that the guidance that speed limits in speed zones should be within 5 mph of the 85th percentile speed be removed.

The ubiquitous sensors that make cities smart can inform the speed limit setting process by confirming who the users of the roadway are, so that posted speed limits address the safety of all known road users.

The Bottom Line

Do away with the historic speed limit setting approach based on outdated research and save lives by embracing a data-driven alternative where pedestrians and cyclists count.

Discussion

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1 Comment

  1. Thanks John for posting this information, particularly the links to the reports. For so long our roads have been assumed to be the strict domain of cars so the point about capturing data on vulnerable road users is critically important. I hadn’t considered that sensors could be used to capture data on pedestrians so perhaps that’s an emerging area that I’m sure will become more sophisticated in the coming years.

    The need for equitable approaches in transportation planning is starkly highlighted by some of the basic stats in the Vision Zero Network’s 2017 Moving from Vision to Action report. African American and Latino people are twice as likely than the white population to be killed while walking and low-income people are twice as likely than high-income people to be killed while walking. Those are dreadful figures! It’s not surprising then to find out that 90% of high income communities have sidewalks as compared to 49% of low income communities. A data driven approach to transportation planning could help pinpoint where this situation most needs to change.

    The Toward an Active California report gets into details that would be helpful for transportation planners in making the necessary changes. Although this document is California focused, it looks as though the strategies can easily be applied in other jurisdictions. It’s especially useful that one or more examples are included (with photos) to show where each strategy has been implemented. I see that it also provides information on various pedestrian modes types. Interesting that a pedestrian is being defined broadly as “any person walking, skateboarding, using a wheelchair or other mobility device, or any other form of human-powered transportation other than a bicycle. Motorized wheelchair users are also considered pedestrians”. That’s a good reminder to be mindful of both traditional new uses of people getting themselves around. The more thinking about pedestrians we do, the better!

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