The Copernican Revolution: A New Model for Highway Safety

In the 15^th century, scholars believed that the earth was the center of the universe and the sun and the other planets rotated around the earth. 

This seemed logical – they lived on the earth and from their vantage point, the sun appeared to be moving, not the earth.  Nicolaus Copernicus saw things from a different perspective.  Copernicus contended that the sun was the center of the universe, not the earth.  His heliocentric model, demonstrated that the observed motions of the planets can be explained without putting the Earth stationary in the center of the universe. Heliocentrism represents a starting point in modern astronomy and a revolution in scientific observations. 

Highway safety is now undergoing a Copernican Revolution of sorts.    For years, highway safety management has centered on crash data.  This seemed logical – the goal of highway safety efforts are to eliminate crashes so crash data should be the starting point.  Engineers and others responsible for highway safety have used crash databases to find locations with high crashes and focused improvement efforts on those locations. 

However, just because an intersection or segment of roadway doesn’t have a reported crash in a database, doesn’t mean that the location is safe.   Crash data are incomplete as many crashes go unreported, patterns are unstable, and location accuracy is often unreliable. 

Just as the earth doesn’t need to be the center of the universe to be important to the human race, crash data doesn’t have to be the center of highway safety management to be important to improving safety.  In highway safety, the universe can have another center.

The Federal Highway Administration is currently conducting a demonstration using roadway inventories as the center of highway safety management.  Roadway inventories are much larger and more robust than crash databases.  A good roadway inventory has information on every segment and intersection in a jurisdiction linked through a common location referencing system, whereas a crash database only includes locations with crashes.  Roadway inventories are also expandable.  That is, as more about a particular location is known or as conditions change, the roadway inventory can expanded or updated.

In this highway safety heliocentric model, the larger, more robust roadway inventory is the sun and the crash database is the earth.  Other relevant databases such as traffic volumes, safety improvement databases, pavement databases, and sign inventories can be considered the planets.  Together with the crash database, these databases can be linked to the roadway inventory for use the same way that Mars, Mercury, Venus, and the Earth rotate around the sun in a solar system. 

This linked solar system of heliocentric data, or Management Information System (MIS), presents numerous opportunities to expand highway safety improvement efforts beyond simple identification and diagnosis of safety by frequency of crashes.  Reported crashes can be combined with traffic volumes to consider exposure in detailed reviews by location type (e.g., all 3-leg signalized intersections).  As more planets (databases) are linked together in the solar system (MIS), more sophisticated analysis can be conducted, presenting numerous opportunities to improve highway safety.  For example, planned paving projects can be reviewed to find segments with run off the road crashes that could be improved by adding rumble strips as part of the repaving.  Unsignalized intersections with close proximity to power can be identified to find locations where adding lighting to reduce nighttime intersection crashes is cost-effective.  The location of horizontal curves can be compared to roadway departure crashes and appropriate signing.  The possibilities, like the universe, are seemingly endless.

Copernicus didn’t get to experience the advances that resulted from his model; it wasn’t until 200 years after his death that heliocentrism was widely accepted.  My hope is that the highway safety community embraces the heliocentric model for highway safety much faster. 

To learn more about the use of roadway inventory data to improve highway safety, please visit the FHWA MIRE website at www.mireinfo.org.

The Mother-in-Law Test

Last summer, we took a beach trip to Ocean Isle, North Carolina.  One afternoon I ventured out with my mother-in-law, Sharon, to get some fresh blueberries.  On the drive back to the beach from Holden Brothers Farm Market I saw a flashing yellow arrow for a left turn at a signalized intersection ahead.  It was the middle of the day and the road was mostly deserted.  I slowed the car and asked Sharon for her thoughts on the signal indication, “Well, it’s yellow so I have the right away, but it’s flashing so it means it’s going to end soon and I should hurry up and turn left.” 

Not even close.  Thankfully, I was the one driving. 

Flashing yellow arrows were recently introduced for permissive left turn movements at signalized intersections.  However, unlike green arrows, the left turning vehicle does not have the right-of-way and instead has to wait for a gap in oncoming traffic before turning left.    

It probably appears at this point that I’m picking on my mother-in-law; I’m not.  In fact, the opposite is true.  Sharon is well-educated, a retired high school teacher with an advanced degree in English.  I value her insight on this topic (and, she reads this blog).   

I started occasionally asking Sharon for her perceptions on traffic control devices over ten years ago.  We were walking in downtown Portland, Oregon.  As we crossed at a signalized intersection Sharon said, “I’ve been meaning to ask you, what does the flashing hand mean on the pedestrian signal?”   I had just finished two national studies on pedestrian countdown signals that included on-street surveys of pedestrians to determine their understanding of traditional pedestrian signals compared to countdown signals.  Sharon’s understanding of the traditional pedestrian signal indication mirrored what I found in my surveys.  Pedestrians understood the WALK indication and the steady DON’T WALK of the traditional pedestrian signal, but didn’t understand the flashing DON’T WALK that is displayed between the two.  The newly introduced pedestrian countdown signals provided a message that was more easily understood.    

Sharon has now become my test case for determining if a traffic control device or other transportation practice makes sense to an educated driver; I call this the mother-in-law test.  I don’t ask my husband because he has spent the last fifteen years listening to me talk about highway safety and his perception would reflect that.  (Similarly, I know enough about finance to be dangerous.)  I find that Sharon represents the understanding of an average, educated driver, living outside of a major metropolitan area like DC, New York, or LA. 

Throughout time, transportation engineers have designed some traffic control devices and configurations that make sense to other engineers, but not necessarily to the driving public.  Although most designs have undergone testing before wide-scale implementation, some slip through the cracks.  In discussing this topic with others, several notable examples have emerged including ramp metering signs, the graphical lane ends sign, milling signs, or the sign pictured at the top of this post.  Although traffic engineers and Bon Jovi fans will recognize this sign as indicating slippery when wet, some drivers perceive this as indicating there are curves ahead. 

So how do we avoid designs that are confusing to the average driver?  I think a good starting point would be to stop asking our fellow traffic engineers, drivers in the DC area, or spouses/significant others if the designs make sense.  Instead, we need to start asking our mothers-in-law. 

Please use the comment box to share other traffic control devices or configurations that are misunderstood.  I’ll pass them on to Sharon for her thoughts.

Hell Roads

What makes a road dangerous?  Seems like a simple question.  A lot of creativity and effort is devoted to this question because understanding the answer is a critical step to improving safety.  Tonight, the Discovery Channel premieres their special, Hell Roads, which also explores this question.  The program will feature eight notorious roads around the globe that are considered some of the most dangerous in the world.  Their website describes the program as:

From around the globe lies eight notorious Hell Roads, each distinct in their own danger and history of carnage. Meet the people whose risk their lives braving avalanches, rockslides, 10,000ft drops and even gunfire as they drive these terrifying highways.

While filming this special, Discovery Channel sought out my colleague, Paul Eng-Wong, to provide some engineering perspective on the topic.  As a Past International President of the Institute of Transportation Engineers, Paul understands the safety issues facing transportation agencies around the world.  The global issues are far from simple, influenced by diverse factors such as terrain, weather, security, economics, and complex social and cultural issues. 

The special airs at 9 PM tonight and will be repeated over the next week. Please visit Discovery Channel’s website for additional listings. 

Conspiracy Theory

Several times a year, the phone rings at the office and someone on the other end has questions for me about the length of the yellow interval for traffic signals.  The call usually goes something like this:

Reporter:  “Hi.  This is Kent Brockman from WXYZ in Shelbyville.  We’re doing a story on the traffic signal timings and were wondering if you could answer some questions for us.”

Me:  “Sure, I’d be happy to help.  What are your questions?”

Report:  “I took a stop watch out to some intersections and think the yellow interval is too short.  I calculated what the interval should be based on the traffic engineering department’s equation, and I get a much longer time.”

Me:  “Okay, let me walk through the calculation with you.  Tell me about the intersection.”

These calls are usually initiated because it’s a slow news day, the local police department announced the start of automated enforcement, or the reporter’s spouse got a ticket for running a red light.  Regardless of the reason, I’m usually glad to help.  Most reporters are very congenial and have made a simple mistake in the calculation.  Although appreciative, some are disappointed after I walk through the calculation with them only to find that the yellow interval at the signal is adequate.  These conversations happen so regularly that I keep a three-ring binder with the derivation of the equations and associated pictures that I fax or email out when needed. 

I also get a few calls a year that are similar, but go a little more like this:

Caller:  “Hi.  This is Lionel Hutz from Springfield.  I’m a traffic safety expert.  Someone gave me your name.  I have some questions about the yellow interval.”

Me:  “Sure, I’d be happy to help.  What are your questions?”

Caller:  “I think there is an error in the yellow interval equation.” 

Me:  “I’d like to hear a little more about why you think there is an error.  But first, how did you get my name?”

Caller:  “The interval is too short.  The calculation has a math error.”

Me:  “Okay…. I don’t think there is a math error but we’ll walk through it together.   Let’s start with the equations of motion and assume we have two cars approaching a signal side by side when the light turns yellow.  One car decides to stop; the other car decides to keep going.  We’re going to set up two equations.  One equation is based on the distance…”

Caller [Interrupting]:  “I’ve looked at that.  There is not enough time for the stopping car to stop.  There is a mistake in the equation.”

At this point, I realize the caller misspoke at the start of the conversation.  When they said they were a traffic safety expert what they really meant to say was ambulance chaser.  However, I usually still try to help, hoping to change a misperception. 

My expertise in the yellow interval started in 2001 after the staff of the U.S. House Majority leader at the time released a report entitled, The Red Light Running Crisis:  Is it Intentional?  The title might lead you to think the report was questioning whether drivers were intentionally violating the signal but instead, the report questioned whether traffic engineers had spent twenty years changing the equation to calculate the yellow interval in order to make money on red light cameras. 

Although I love a good conspiracy theory, two months of research at the Library of Congress unearthed that the equation used by most agencies (referred to as the kinematic equation) was based solidly on the equations of motion and the best available research about driver’s reactions and vehicle capabilities.  The inputs to the equation have changed through the years in response to updates in research from what was available in the 1920s.   For example, one of the largest changes happened about 20 years ago when the rate at which vehicles stopping were assumed to decelerate was lowered.  (This changes causes a lot of raised eyebrows but actually resulted in longer intervals because vehicles that decelerate slower need a longer distance.)

Based on our work, Hugh McGee and I wrote the congressional testimony to address the allegations in the report.  This testimony was eventually published as “A History of the Yellow and All-Red Interval.”  With the help of Google, this publication is usually how reporters get my name. 

The history of the yellow interval is about to add another chapter.  In a few months, the results of a National Cooperative Highway Research Program project (NCHRP 3-95) on the subject will be published.  Hugh McGee is the Principal Investigator of the study which developed a comprehensive and uniform set of recommended guidelines for determining safe and efficient yellow change and red clearance (i.e., all-red) intervals at signalized intersections.  The guidelines are insightfully based on lots and lots and lots of observations of drivers approaching signals at the onset of the yellow interval around the U.S. 

At the TRB Annual Meeting this year, you can get an advance look at the findings in two presentations.  My friend and Hugh’s teammate on this project, Dr. Tim Gates from Wayne State University, will present the findings of the field studies on perception-reaction, deceleration rate, and approach speed in the presentation A Comprehensive Evaluation of Driver Behavior to Establish Parameters for Timing of Yellow Change and Red Clearance Intervals.  In a second presentation, my colleague and friend at VHB, Kevin Moriarty, will present the guidelines in Guidelines for Timing Yellow and Red Intervals at Signalized Intersections.

This promises to be one of the best sessions at TRB, although if you’re hoping for a conspiracy, you’ll have to look elsewhere.   

Pep Rally

January can be a long month in some professions.  The holidays have passed and for most parts of the country, the cold weather and gray skies have set in.  In transportation research, the return to the office means it’s time to start planning for a pep rally– the Transportation Research Board (TRB) Annual Meeting.  This year marks the 91^st Annual TRB Meeting.  Held annually in Washington, D.C., TRB draws around 11,000 transportation professionals from around the world to learn about the latest research in all aspects and modes of transportation.

My company, VHB, is proud to be an affiliate member of TRB.  Many of my coworkers attend the annual meeting, several presenting or participating in the important work of the technical committees.  This includes my colleague, Walter Kraft, from our Newark office.  Walter, an expert in transportation operations, has attended at least the last 40 consecutive meetings.  (He’s actually lost count but he knows it’s over 40). 

The meeting organizers, recognizing the value of Walter’s experience, asked him to provide a consultant’s perspective at one of the opening events of this year’s conference.  Entitled So You Want to be a Transportation Professional, the event is a workshop designed to give young professionals entering or considering the profession an opportunity to interact with professionals like Walter and learn about possible career paths. 

My first TRB meeting was while I was an undergraduate at Michigan State University.  I had spent the previous summer as a transportation intern for a local municipality.  I enjoyed the job and the people I worked with but I didn’t see any opportunity to impact highway safety.  My experiences were so limited at that point, I concluded just from that summer job that a career in transportation wasn’t for me.  My academic schedule for the following year included highway design.  Although my thoughts had turned to structures and math at that point, I left the class on my schedule anyway. 

Highway design was taught by former State DOT designer, Dr. Tom Maleck. Enthusiastic about transportation, Dr. Maleck organized an annual trip to TRB for his students.   I attended the conference with the rest of my classmates because it was an excuse to visit D.C.  The metropolitan city was the perfect back drop to the conference.  The ultra clean and efficient metro, filled with young professionals on their way to work in the Nation’s capital, whisked us from our hotel in Arlington to the conference hotel in Woodley Park.  Inside the hotel, policy makers, administrators, practitioners, researchers, and representatives of government, industry, and academic institutions met to discuss ideas.  My classmates and I attended numerous presentations in rooms filled to capacity with people who wanted to hear other professionals present their research and engage in a discussion (and some, in a debate) about the findings.  Absolutely unexpectedly, the conference inspired me. 

I’ve attended the meeting every year since, including when I was 9 months pregnant with my first child.  This year will be my 16^th consecutive TRB.  (I realize that compared to Walter, I’m still a novice.) 

I’m greatly looking forward to this year’s meeting, now only 14 days away.  Several of my colleagues and friends in the industry are presenting their findings.  I’m excited to hear what they have to say; I know I’ll leave inspired once again. 

If you are interested in learning more about TRB, please visit their website at www.trb.org.  If it’s your first TRB, prepare to be inspired and be sure to attend Walter’s workshop (Workshop 148, 1:00 PM on Sunday at the Marriott Woodley Park). 

Happy New Year

Most media outlets spend the week leading to today recapping the top stories of the past year.  There were the typical news roundups that cited the top news stories, movies, and celebrities but there were also very specific reflections on 2011 such as the word of the year (tergiversate just edged out occupy) and the top 10 Google searches of the year. I had a difficult time finding any transportation safety roundabouts so I decided to make my own using a word cloud. 

This word cloud is my attempt to capture the top stories in transportation in 2011.  I generated it from the U.S. DOT Secretary’s blog, The Fast Lane.  A word cloud uses the words in the posts from the last year to identify the topics and themes that were discussed. Safety is prominent in the word cloud.  Technology, innovation, and research are also collectively very prominent.  Drivers and vehicles are more prominent than infrastructure, which is a little surprising given that our nation’s aging infrastructure was catapulted front page headlines just over four years ago with the collapse of the 1-35W bridge in Minneapolis.  The word cloud also reflects the blog’s coverage of efforts in several States to ban cell phones and driving while texting.  From my perspective, this was a large theme in 2011 with some labeling distracted driving the new intoxicateed driving. 

Other notable national transportation safety themes in 2011 included:

·         Funding.  The future of transportation spending and the impact on safety was and will continue to be an important theme as many agencies are trying to determine how the next transportation funding bill will address safety.

·         Blips?  Several States experienced an increase in fatal crashes in 2011 after several years of steady decreases nationally.  Various news stories questioned if these were statistical blips or the start of a new upward trend in these States.

·         Smarter Vehicles.  Several automakers introduced vehicles with technologies to prevent crashes including cars that can detect collisions are imminent and initiate braking themselves. 

Although not national news, other themes in 2011 included the increased use of the flashing yellow arrow for permitted movements, the development of new crash modification factors and guidance on their use, and the start of integration of the Highway Safety Manual (HSM) by State and local agencies.

What will be the guiding theme for highway safety in 2012?  I predict we’ll see an increased focus on the importance of data, including expanded applications of spatial data.    I also predict that crash modification factors and the use of the HSM will continue to evolve, in-vehicle technologies such as GPS will be better recognized as contributing to distracted driving, older driver issues will become acute, and the blips will be recognized as trends. 

Please use the comment box to add your own predictions for 2012.  Feel free to add in flying cars or the like.