(Disclosure: Summit Land Management is a Rose Law Group-related company, and contracted with the firm.)
One of the professional organizations (Women in Transportation Seminar) vital to my continuing professional development recently sent an informational notice regarding predicting potential high-collision locations. Preventing and reducing traffic collisions is a critical requirement for all traffic engineers. Our profession is always seeking techniques to improve safety.
Two books I have recently read were written by self-critical traffic engineers, each with a long tenure as a decision-making professional traffic engineer. One was published in 2024, with the title, “Killed By a Traffic Engineer.” The other was published in 2021 with the title “Confessions of a Recovering Engineer.” Both books emphasize the need for traffic engineers to continually observe driver behavior, analyze collision data, and objectively evaluate street design.
Traffic collisions seem to be inherent to life in the modern United States. We all hear daily radio and television reports of traffic accidents somewhere in our metropolitan Valley of the Sun. Our first interest in these stories is whether or not these incidents affect our travel that day. When traffic engineers, police officers, fire fighters, and ambulance drivers hear these reports, our first thought is that some of our fellow Earth-dwelling humans, and their loved ones, have had their lives disrupted, perhaps seriously and permanently.
In the ASU undergraduate and graduate traffic engineering courses I frequently have the honor of teaching (since 1996), I always discuss traffic collision analysis. Some semesters, I discuss a presentation I gave to the City of Scottsdale Transportation Commission, as Scottsdale Transportation Director, back in mid-2019. In an 18-month period in 2018 and 2019, there were 23 traffic collisions involving fatal injuries. A council member requested that the Transportation Department investigate those collisions and discover preventative measures.
Of those 23 fatal collisions: 7 involved pedestrians, 4 involved motorcycles, 2 involved school buses, 1 involved a bicyclist, 1 involved a horse trailer, and 1 involved a house trailer. Five of the 23 collisions were single vehicles whose driver drove off the road. Four of those drivers hit a roadside object such as a large sign or light pole. The fifth driver actually had a heart attack while driving and was able to pull off the road onto a shoulder before he died. Three of the 23 collisions involved a driver crossing into the opposing traffic lanes and causing a head-on collision.
The 2 collisions involving school buses occurred because the other vehicle was exceeding the speed limit. One of the 2 collisions occurred because a speeding motorcyclist did not see the school bus turning left off of an intersecting street and drove into the side of the school bus. The other collision involved a speeding small truck that rear-ended a school bus that was stopped to allow students to exit the bus. Witnesses to this collision informed the investigating police officer that the small truck had been following the school bus for several miles.
One fatal injury occurred in the Westworld parking area. A person was backing their truck, towing a house trailer, into a parallel parking space. The driver’s spouse was directing the driver into the parking space when the driver backed their house trailer into their spouse.
The fatal injury involving a small truck towing a horse trailer occurred on a one-lane-per-direction portion of Dynamite Boulevard at night. The person driving the small truck with a horse trailer attempted a U-turn and was struck by another small truck.
Another fatal injury collision occurred when one driver did not stop on a red light and hit another vehicle.
A particularly sad fatal injury occurred on Indian School Road west of Old Town, when two people were driving home from a night in the Entertainment District. Evidently, the two people were quarreling and the passenger exited the vehicle while the car was traveling at 40 miles-per-hour.
Another particularly sad fatality occurred when an elderly person coming home from work on the bus, exited the bus, then attempted to walk across six lanes of 40 miles-per-hour traffic. She never made it to the other side of the street. (This location now has a Pedestrian Hybrid Beacon to allow pedestrians to cross safely).
Three collisions were left-turn-head-on collisions. These occur when one vehicle is turning left and hits or is hit by an opposing through-vehicle. All three of these collisions involved motorcycles.
Sometimes the person who caused a collision is the person who died. In other collisions, the person who lost their life did not cause the collision.
This presentation ends with a video from a photo-enforcement camera. Every year I show this video to a high school class. Before I show the video, I ask the students if they are opposed to photo-enforcement. Almost always, a very high percentage of the students raise their hands. Then I show the video. One driver is turning left and is hit by an opposing vehicle driving straight. The vehicle driving straight entered the intersection 9.62 seconds after their traffic signal turned red. The speed limit on the street was 45 miles-per-hour. The driver of the straight vehicle was traveling at 70 miles-per-hour. After the video, I ask the students again if they are opposed to photo-enforcement. Rarely does anyone raise their hand the second time.
People often tell me that we should do everything possible to eliminate fatal traffic accidents. I tell them that we should require all cars to have a maximum speed of 25 or 30 miles-per-hour. Suddenly, they no longer want us to do everything possible to eliminate fatal traffic accidents.
Most of those 23 fatal traffic accidents in the City of Scottsdale in 2018 and 2019 occurred because of high travel speeds. Photo-enforcement of speed limits has been proven, through detailed multi-year analysis, to reduce collisions. Yet many people and lawmakers oppose the use of photo-enforcement.
In 2024, there were a total of 314,895 collisions in the state of Arizona reported to the Arizona Department of Transportation. The highest driver violation was either “Speed Too Fast For Conditions” or “Exceeded Lawful Speed” at 23%. The next highest driver violation was “Failed to Yield Right-of-Way” at 8%. This violation most often occurs by a left-turning driver. “Distracted Driving” was at 3% – though the police only know if a driver was distracted if the driver or a passenger admits it. All other driver violations were 2% or less of the total 314,895 collisions.
When I was a consulting traffic engineer from 2004 to 2010, Rio Salado Parkway was the street adjacent to our building, the exclusive access to our building, the street every person in our office drove twice every working day. One time, the speed limit on Rio Salado Parkway was changed by the City of Tempe. During a monthly manager’s meeting, in a conference room overlooking Rio Salado Parkway, I asked if anyone knew the previous speed limit and the new speed limit. Many of the two-dozen people in the room did not know the speed limit had changed. I was the only person in the room who knew both speed limits. I was also the only traffic engineer in the room. (Previously, the speed limit was 40 miles-per-hour, and it was changed to 35 miles-per-hour).
Most people who drive never notice the speed limit, even though many modern cars display the speed limit on their dashboard. Speed limits are irrelevant to us. Many of us simply do not think we need to be aware of the speed limit on a street. For many of us who are aware of the speed limit, we do not think we need to obey it. There are few consequences for not knowing the speed limit or for violating the speed limit. Both collisions and tickets are rare. Traffic engineers, police officers, fire fighters, and ambulance drivers know that speed limits and travel speeds matter.
I believe two reasons exist for drivers to ignore speed limits. First, interstate highways typically have a design speed of 80 miles-per-hour. Subconsciously, we know the street is safe at speeds greater than the speed limit of 55 or 65 miles-per-hour. So, we drive faster than the speed limit. Since virtually all of us in the United States regularly drive on freeways, we are accustomed to ignoring speed limits, and do so on all streets. The book “Killed By A Traffic Engineer” discusses this problem. The author maintains that city streets should have much lower design speeds, which will then force drivers to drive slower.
The second reason is the common knowledge that police will not cite a driver for speeding unless they are traveling more than 11 miles-per-hour over the speed limit. Except in 15 miles-per-hour school zones where drivers traveling at 16 miles-per-hour are cited. Evidently, school age pedestrians are more important than the rest of us.
In a perfect world, the freeway speed limits would all be 75 miles-per-hour. With changeable speed limits, the speed limit would be lowered during high congestion times at specific locations. (Seattle uses this technique in their downtown areas.) Posted speed limits on all streets would be enforced by photo-enforcement, and would cite drivers when their travel speeds are more than 5 miles-per-hour over the posted speed limit. As every person who has been a parent of one or more young children knows, us humans sometimes need reminders to properly behave. Again, should we do everything possible to eliminate fatal traffic accidents?
For most of those 23 fatal traffic collisions in the City of Scottsdale in 2018 and 2019, there was nothing a traffic engineer could have done to prevent those collisions. They were caused by someone driving poorly. Typically, two drivers making mistakes are necessary for a collision to occur, though sometimes, only one driver needs to make a mistake to cause a collision. More than 90% of traffic accidents are caused by human error. Hence the need for artificial intelligent, self-driving cars. The author of “Killed By A Traffic Engineer” claims that because traffic engineers use such high design speeds for roads, they lull drivers into a false sense of safety which then creates their mistakes.
Left-turn-head-on collisions are the most troubling type. It is difficult to see past opposing left-turning vehicles to know if there is an oncoming vehicle. Most traffic engineers, including me, avoid turning left. I’ve noticed that when I am walking, even in buildings, I avoid left-turns. Evidently, both United Parcel Service delivery trucks and Amazon delivery trucks are routed to avoid left-turns.
Some traffic engineers advocate that left-turns should only be allowed on green left-turn arrows, with a red left-turn arrow displayed all other times. This requires all drivers to wait to turn left when they can see clearly that there are no oncoming vehicles. Should we do everything possible to eliminate fatal traffic accidents?
Like most traffic engineers, police officers, fire fighters, and ambulance drivers, I vividly recall certain traffic accidents on the streets that were my responsibility from as long as 35 years ago. Every working day, I remember at least four names of people killed or seriously injured in traffic accidents on Scottsdale streets when I was Scottsdale Traffic Engineer from 1984 through 2000.
The first traffic accident in the world occurred in 1771 in France. The first traffic accident resulting in a fatality occurred in Ireland in 1869. The first traffic accident in the United States occurred in 1891 in Ohio City, Ohio. The first pedestrian fatality in the United States occurred in 1899 in New York City.
(Interesting trivia. The now Los Angeles Dodgers were called the Brooklyn Trolley Dodgers in 1895, because their fans, as pedestrians, were expert at dodging the electric trolleys, which replaced horse-drawn trolleys in Brooklyn in 1892. Though, the name “Dodgers” appeared on both their home and away jerseys for the first time in 1933.)
From the 1930’s through 2010, traffic engineers examined only past traffic collisions in an attempt to prevent future traffic collisions. This methodology only examined past – either recent or distant – collisions. So, the collisions had to occur before they could be prevented. In 2010, the Federal Highway Administration published the Highway Safety Manual. This document was the first formal attempt to predict future traffic collisions before they occurred, then discover and implement methods to prevent those collisions. The second edition was published in 2024. These attempts have been helpful, though the prediction methodologies are understandably less-than-perfect.
The Governors Highway Safety Association was originally created by the Federal Government in 1966. In September of this year, this association, in cooperation with Cambridge Mobile Telematics, released a report discussing available data that can identify driver behaviors that lead to collisions. Because of the proclivity of mobile phone use; driver data exists for speeding, hard braking, aggressive driving, and distraction. These data were aggregated to ensure that individual drivers were not identified. Though, some insurance companies use these data to reduce premiums for safe drivers and increase premiums for unsafe drivers. Again, should we do everything possible to eliminate fatal traffic accidents?
The Governors Highway Safety Association and Cambridge Mobile Telematics report suggest that these driver behavior data can identify locations where roadway improvements are necessary, such as pavement markings that should be painted or replaced, warning and stop signs that should be repositioned or added, or traffic signals that should be installed or modified. Further, after changes have been implemented, the data can reveal if driver behavior has improved or if further changes are necessary.
Predictive analytics of the data can also be used for public awareness or social media campaigns focused on people who drive or reside in areas where poor driving occurs. The report advocates for states to enact or strengthen laws requiring seat belt use and laws prohibiting hands-on cellphone use. Again, comparative data can be analyzed to determine if the public awareness campaigns have been effective or should be modified.
The Governors Highway Safety Association Chief Executive Officer stated, “this is an action plan to prevent crashes — not just respond to them.” “The advanced analytics we outline are validated, predictive, and provide a level of foresight that past generations of safety leaders could only imagine.”
Traffic fatalities are measured in fatal collisions per 100-million-vehicle miles. So, a fatality rate of 1 means that 99,999,999 miles are traveled without a fatality for every 1 fatal collision. So, while fatal collisions are always tragic, they are quite rare. Of course, if you or a loved one is the killed person, the statistics are irrelevant. The first year that fatal collisions per 100-million-vehicle miles were measured in the United States was 1921, when 13,253 people were killed in vehicle crashes with a rate of 24.08 fatalities per 100-million-vehicle miles. The number of people dying in United States traffic accidents increased continuously from 1921 through 2005 when 43,510 people were killed. The fatality rate decreased by approximately 10% per year during the 1920’s, then by approximately 2% per year during the 1930’s through the 1970’s. The fatality rate decreased by 5% to 10% during the 1980’s and 1990’s, then decreased by 2% to 5% annually through the 2000’s and 2010’s. In 2019; there were 36,355 traffic fatalities for a rate of 1.11 fatalities per 100-million-vehicle miles. In 2023, there were 40,901 traffic fatalities; an increase of approximately 3% per year from 2019 to 2023.
From 1899 through 2023, 3.997 million people were killed on United States roadways. By comparison, the total number of United States military personnel killed in wars from the Revolutionary War through January 2025 is 1.305 million.
Yes, we need to change our behavior.
