Category Archives: TED Talks

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This post is a little different from my usual content.


My dissertation research focus is on alternative intersection designs, and I am committed to spreading the word about these designs as far as I can.  To this end, I am nominating myself to speak at the upcoming Virginia Tech TEDx event on November 10, 2012.  Speakers will be chosen from among the students, faculty, and staff at the University.  I’ve written a first draft for the presentation I wish to give, should I be chosen to participate in the event.  It’s designed to be around 15 minutes in length, so it’s not a quick read.  If you have the time, I strongly suggest you read the post because I feel that the information is important.  If you are a student, alumnus, faculty, or staff member at Virginia Tech, and you agree that this information should be presented at the upcoming TEDx event, I would be very grateful if you could add your nomination to my own before the May 18th nomination deadline arrives.


Thank you,  John

Good afternoon, my name is John Sangster, and I’d like to start off my talk today with a confession: I like traffic. When I tell people that I’m a traffic engineer, the way I’m sometimes looked at makes me understand how divorce lawyers must feel; everyone knows that our jobs are necessary, but everyone wishes that they weren’t. Okay, so what’s that I said about liking traffic?

It’s not that I enjoy traffic because it gives me more time to listen to NPR, I’ve got my driveway for that. I like traffic because each car on the road means people are busy living their lives. Traffic is created whenever we have places to live, jobs to go to, money to buy groceries with, and play-dates to take our kids to. Sometimes I feel like each car on the road is like a small proclamation of productivity.

The reason I have a job, and the reason why I am here today to talk with you, is that individual trips are wonderful things, but having more than one car on the road naturally leads to conflict. Lots of cars on the road at the same time leads to lots of conflict. This idea of conflict is used within my industry to better understand and control the flow of traffic on the roads. The next time you drive through an intersection, I’d like you to ponder this concept of conflict.

Source: Federal Highway Administration

The simplest of intersections, with only one lane approaching from each direction, contains 32 different points of conflict. Each time you go straight through an intersection, there are six different points where you are passing through the path of another vehicle. The first two points are called diverging points, where cars traveling on the same path separate into different paths. These diverging points are a source of rear-end collisions, when a following vehicle makes an assumption that the leader will continue through, and for some reason the leading vehicle is forced to stop. The next four points of conflict you pass through are called crossing points; these locations are the most dangerous, and are the cause of head-on and T-bone collisions. The last two points you pass through are a bit less stressful; they’re called merging conflict points, and involve vehicles from separate paths coming together to move in the same direction; these conflicts usually result in side-swipe collisions, and are usually limited to property damage with many fewer injuries or deaths. The reason I want you to think about these conflicts when you’re out on the road driving, is because I’d like you to be a little more patient when waiting at a red light. There are good reasons for signalizing an intersection, and one of the best is to make sure that the other cars driving through it aren’t going to be in conflict with you!

Source: Federal Highway Administration

Tolkien was wrong; it takes two rings to rule them all. Common practice in the United States is to organize traffic movements according to the “ring and barrier design” as shown in the graphic. The power of the conceptualization is that it separates all of those conflicts we discussed so that nothing overlaps. Each individual movement cannot occur simultaneously with any movement in its row, or any movement located on the other side of a barrier from it. For example, movement one, a northbound left-turn, can only occur simultaneously with movements five or six, a southbound left-turn or a northbound through/right movement.

Now the world is in balance: we’ve got conflict, and we’ve got a control scheme to fix it; right? So how successful have traffic engineers been at keeping you safe on the roads? Not very.

The leading cause of death in the United States for people between the ages of 15 and 44 is motor vehicle fatalities. Let me say it again more slowly, because this is heart-wrenching for me; the leading cause of death for young people is from driving. According to the Federal Highway Administration, there were 2.5 million intersection-related crashes in 2007, 37,000 of which resulted in a fatality. For crashes resulting in injury or death, the highest rate is among 16-year old drivers, who experience 61.4 crashes per 1,000 drivers. I have trouble conceptualizing how much 61 out of 1,000 is, but I find it very easy to understand when put another way.

Among high school juniors, one student out of every sixteen will be behind the wheel of a car that is involved in a crash in which someone is injured or killed. I like the way that this image makes the statistic more relatable, but it still feels impersonal to me. I have three incredibly important, and very personal, reasons for the work that I do.

My son Jonas loves reading non-fiction books – his current favorite topic is space and the planets. His favorite color is orange. When he arrives at pre-school in the morning, he likes to sit on a bench for the first five minutes by himself quietly watching the other kids play before he ventures out to join them. He will be eligible to get his driver’s license in July of 2024.

My daughter Emily is extremely friendly and very polite, so long as you’re doing exactly what she wants. She likes to wear “piggy tails,” though she rarely sits still while I fix her hair in the morning. Her favorite color is purple. She likes to browse books at bedtime, and nearly every time I go in to turn out her light she’s got a book lying on her face. She will be eligible to get her driver’s license in April of 2026.

My son Isaac likes to sit on my lap and chat with me. I’m not sure what he’s saying most of the time; he keeps talking about some lady named “Nnnnnga” that I have yet to meet. He’ll be eligible to get his driver’s license in February of 2028.

I tell you these details because my children are not statistics, they are people; they are my life, and I would do anything to keep them safe.

I’ve now taken eight minutes of your time. I’ve explained why traffic can be a positive thing and should be valued, how it creates conflict, and how traffic engineers have been trying to control that conflict. I’ve explained the extent to which we’re failing to keep you safe, and why it’s personally important to me to change it. With the seven minutes that remain of my allotted time, I’d like to talk to you about recent developments in intersection design, which I believe to be part of the solution.

In the last five years a group of intersection designs have been given their own classification as “alternative intersections.” These designs have names like the Jughandle, the Median U-turn, the Restricted Crossing U-turn, the Displaced Left-turn, the Quadrant Roadway, and one that should be very familiar to the audience here today, the Modern Roundabout. Some of these designs have been regionally accepted for many years, such as the Jughandle in New Jersey or the Median U-turn in Michigan, but I’d like to focus the talk today on the two designs which have been gaining wider acceptance only recently. I’ll finish up by talking about the use of the Restricted Crossing U-turn design, but at the moment I want to discuss some of the finer points of the Modern Roundabout.

Source: Google Maps

I’m careful to specify this design as the modern roundabout, because it’s very different from the rotaries popular in the northeastern US fifty years ago. The diameter of the circle in this design is set as small as possible; only large enough to force cars to slow down as they travel through the intersection. Vehicles traveling through a roundabout are hard-pressed to travel above 20 miles an hour, which greatly increases safety, but this is not the most dramatic safety effect that we see.

If you remember only one thing from today’s presentation, I want it to be the image on the screen right now. Traffic begets conflict, there’s no escaping it, so traffic engineers attempt to control it. We fail at this, and people die. The reason why so many places are embracing the roundabout is that we go from 32 points of conflict to 8, and we completely remove all of the incredibly dangerous crossing conflicts. Accidents still happen at roundabouts, but the angle-type accidents that occur result in far fewer injuries and deaths.

As Americans we’re often known for embracing innovation. I’ll point to the state of Virginia as a positive example of this: in 2004 the first modern roundabout intersection was constructed in the state, and by 2008 the State’s road design manual was updated to say that whenever a roundabout will work for a given location, the state prefers it over the conventional design. I was pretty impressed when I found this out, because it feels like a huge accomplishment to make that large of a policy shift in a four year period. As fast as we’re adopting the design though, we’re still way behind the curve. The latest number I’ve seen says that the United States has installed 3,000 of these intersections; in contrast, there are 25,000 of them in the United Kingdom, and 30,000 of them in France. So why aren’t we replacing every signalized intersection with a roundabout? It’s because the roundabout is not a silver bullet; it performs wonderfully up to a certain level of traffic flow, working particularly well at places with lots of turning vehicles, but it doesn’t make sense in every situation.

Source: see ATTAP for video

In some cases where a major street and a minor street meet, there’s too much through traffic on the major street to accommodate a roundabout and we need a different solution. North Carolina has been using the Restricted Crossing U-turn on high-volume roads for a couple of years now, and they’re happy with the results. This design allows major street traffic to move in any direction it wishes, but makes the minor street approaches turn right, forcing them to make a U-turn down the road if they intend to cross through to the other side or take a left-turn. The ring-and-barrier design I discussed earlier comes into play here: by getting rid of the left-turn phase on the minor street approach more of the green-time can be given to the major street traffic. A small number of vehicles approaching on the minor streets take a much longer time to travel through the intersection, but a large number of vehicles approaching on the major street take a bit shorter time traveling through, generally breaking even overall. We’ve checked off the “do no harm” requirement for traffic mobility, so how does it perform for safety?

Source: Federal Highway Administration

This design isn’t as clean as a roundabout for safety, but it’s better than a conventional intersection, and it works in situations a roundabout does not. In all, we reduce the conflict points from 32 to 20, with the all-important crossing conflicts reduced from 16 down to 2. This is just an example of the types of designs that are available to replace our antiquated conventional signalized intersections.

You’ve given me fifteen minutes of your time and I greatly appreciate it, but I have a favor to ask of you. I need you to tell your friends about this; I need you to tell your colleagues about this; I need you to tell your elected officials about this. We can’t wait any longer to embrace these alternative designs. People are dying, our youth are dying, and we need to fix it. I can stand up here and talk until my voice goes hoarse about why we should build these and what is at stake, but I can’t change the world without your help. I want my children, all of our children, to become joyous sources of traffic: driving to school or their summer job, taking their dates to prom, or going on a road trip. I’m anguished over the thought of them becoming an injury or fatality statistic, and I need your help to keep them safe. Thank you. Continue reading →

This post is a little different from my usual content.


My dissertation research focus is on alternative intersection designs, and I am committed to spreading the word about these designs as far as I can.  To this end, I am nominating myself to speak at the upcoming Virginia Tech TEDx event on November 10, 2012.  Speakers will be chosen from among the students, faculty, and staff at the University.  I’ve written a first draft for the presentation I wish to give, should I be chosen to participate in the event.  It’s designed to be around 15 minutes in length, so it’s not a quick read.  If you have the time, I strongly suggest you read the post because I feel that the information is important.  If you are a student, alumnus, faculty, or staff member at Virginia Tech, and you agree that this information should be presented at the upcoming TEDx event, I would be very grateful if you could add your nomination to my own before the May 18th nomination deadline arrives.


Thank you,  John

Good afternoon, my name is John Sangster, and I’d like to start off my talk today with a confession: I like traffic. When I tell people that I’m a traffic engineer, the way I’m sometimes looked at makes me understand how divorce lawyers must feel; everyone knows that our jobs are necessary, but everyone wishes that they weren’t. Okay, so what’s that I said about liking traffic?

It’s not that I enjoy traffic because it gives me more time to listen to NPR, I’ve got my driveway for that. I like traffic because each car on the road means people are busy living their lives. Traffic is created whenever we have places to live, jobs to go to, money to buy groceries with, and play-dates to take our kids to. Sometimes I feel like each car on the road is like a small proclamation of productivity.

The reason I have a job, and the reason why I am here today to talk with you, is that individual trips are wonderful things, but having more than one car on the road naturally leads to conflict. Lots of cars on the road at the same time leads to lots of conflict. This idea of conflict is used within my industry to better understand and control the flow of traffic on the roads. The next time you drive through an intersection, I’d like you to ponder this concept of conflict.

Source: Federal Highway Administration

The simplest of intersections, with only one lane approaching from each direction, contains 32 different points of conflict. Each time you go straight through an intersection, there are six different points where you are passing through the path of another vehicle. The first two points are called diverging points, where cars traveling on the same path separate into different paths. These diverging points are a source of rear-end collisions, when a following vehicle makes an assumption that the leader will continue through, and for some reason the leading vehicle is forced to stop. The next four points of conflict you pass through are called crossing points; these locations are the most dangerous, and are the cause of head-on and T-bone collisions. The last two points you pass through are a bit less stressful; they’re called merging conflict points, and involve vehicles from separate paths coming together to move in the same direction; these conflicts usually result in side-swipe collisions, and are usually limited to property damage with many fewer injuries or deaths. The reason I want you to think about these conflicts when you’re out on the road driving, is because I’d like you to be a little more patient when waiting at a red light. There are good reasons for signalizing an intersection, and one of the best is to make sure that the other cars driving through it aren’t going to be in conflict with you!

Source: Federal Highway Administration

Tolkien was wrong; it takes two rings to rule them all. Common practice in the United States is to organize traffic movements according to the “ring and barrier design” as shown in the graphic. The power of the conceptualization is that it separates all of those conflicts we discussed so that nothing overlaps. Each individual movement cannot occur simultaneously with any movement in its row, or any movement located on the other side of a barrier from it. For example, movement one, a northbound left-turn, can only occur simultaneously with movements five or six, a southbound left-turn or a northbound through/right movement.

Now the world is in balance: we’ve got conflict, and we’ve got a control scheme to fix it; right? So how successful have traffic engineers been at keeping you safe on the roads? Not very.

The leading cause of death in the United States for people between the ages of 15 and 44 is motor vehicle fatalities. Let me say it again more slowly, because this is heart-wrenching for me; the leading cause of death for young people is from driving. According to the Federal Highway Administration, there were 2.5 million intersection-related crashes in 2007, 37,000 of which resulted in a fatality. For crashes resulting in injury or death, the highest rate is among 16-year old drivers, who experience 61.4 crashes per 1,000 drivers. I have trouble conceptualizing how much 61 out of 1,000 is, but I find it very easy to understand when put another way.

Among high school juniors, one student out of every sixteen will be behind the wheel of a car that is involved in a crash in which someone is injured or killed. I like the way that this image makes the statistic more relatable, but it still feels impersonal to me. I have three incredibly important, and very personal, reasons for the work that I do.

My son Jonas loves reading non-fiction books – his current favorite topic is space and the planets. His favorite color is orange. When he arrives at pre-school in the morning, he likes to sit on a bench for the first five minutes by himself quietly watching the other kids play before he ventures out to join them. He will be eligible to get his driver’s license in July of 2024.

My daughter Emily is extremely friendly and very polite, so long as you’re doing exactly what she wants. She likes to wear “piggy tails,” though she rarely sits still while I fix her hair in the morning. Her favorite color is purple. She likes to browse books at bedtime, and nearly every time I go in to turn out her light she’s got a book lying on her face. She will be eligible to get her driver’s license in April of 2026.

My son Isaac likes to sit on my lap and chat with me. I’m not sure what he’s saying most of the time; he keeps talking about some lady named “Nnnnnga” that I have yet to meet. He’ll be eligible to get his driver’s license in February of 2028.

I tell you these details because my children are not statistics, they are people; they are my life, and I would do anything to keep them safe.

I’ve now taken eight minutes of your time. I’ve explained why traffic can be a positive thing and should be valued, how it creates conflict, and how traffic engineers have been trying to control that conflict. I’ve explained the extent to which we’re failing to keep you safe, and why it’s personally important to me to change it. With the seven minutes that remain of my allotted time, I’d like to talk to you about recent developments in intersection design, which I believe to be part of the solution.

In the last five years a group of intersection designs have been given their own classification as “alternative intersections.” These designs have names like the Jughandle, the Median U-turn, the Restricted Crossing U-turn, the Displaced Left-turn, the Quadrant Roadway, and one that should be very familiar to the audience here today, the Modern Roundabout. Some of these designs have been regionally accepted for many years, such as the Jughandle in New Jersey or the Median U-turn in Michigan, but I’d like to focus the talk today on the two designs which have been gaining wider acceptance only recently. I’ll finish up by talking about the use of the Restricted Crossing U-turn design, but at the moment I want to discuss some of the finer points of the Modern Roundabout.

Source: Google Maps

I’m careful to specify this design as the modern roundabout, because it’s very different from the rotaries popular in the northeastern US fifty years ago. The diameter of the circle in this design is set as small as possible; only large enough to force cars to slow down as they travel through the intersection. Vehicles traveling through a roundabout are hard-pressed to travel above 20 miles an hour, which greatly increases safety, but this is not the most dramatic safety effect that we see.

If you remember only one thing from today’s presentation, I want it to be the image on the screen right now. Traffic begets conflict, there’s no escaping it, so traffic engineers attempt to control it. We fail at this, and people die. The reason why so many places are embracing the roundabout is that we go from 32 points of conflict to 8, and we completely remove all of the incredibly dangerous crossing conflicts. Accidents still happen at roundabouts, but the angle-type accidents that occur result in far fewer injuries and deaths.

As Americans we’re often known for embracing innovation. I’ll point to the state of Virginia as a positive example of this: in 2004 the first modern roundabout intersection was constructed in the state, and by 2008 the State’s road design manual was updated to say that whenever a roundabout will work for a given location, the state prefers it over the conventional design. I was pretty impressed when I found this out, because it feels like a huge accomplishment to make that large of a policy shift in a four year period. As fast as we’re adopting the design though, we’re still way behind the curve. The latest number I’ve seen says that the United States has installed 3,000 of these intersections; in contrast, there are 25,000 of them in the United Kingdom, and 30,000 of them in France. So why aren’t we replacing every signalized intersection with a roundabout? It’s because the roundabout is not a silver bullet; it performs wonderfully up to a certain level of traffic flow, working particularly well at places with lots of turning vehicles, but it doesn’t make sense in every situation.

Source: see ATTAP for video

In some cases where a major street and a minor street meet, there’s too much through traffic on the major street to accommodate a roundabout and we need a different solution. North Carolina has been using the Restricted Crossing U-turn on high-volume roads for a couple of years now, and they’re happy with the results. This design allows major street traffic to move in any direction it wishes, but makes the minor street approaches turn right, forcing them to make a U-turn down the road if they intend to cross through to the other side or take a left-turn. The ring-and-barrier design I discussed earlier comes into play here: by getting rid of the left-turn phase on the minor street approach more of the green-time can be given to the major street traffic. A small number of vehicles approaching on the minor streets take a much longer time to travel through the intersection, but a large number of vehicles approaching on the major street take a bit shorter time traveling through, generally breaking even overall. We’ve checked off the “do no harm” requirement for traffic mobility, so how does it perform for safety?

Source: Federal Highway Administration

This design isn’t as clean as a roundabout for safety, but it’s better than a conventional intersection, and it works in situations a roundabout does not. In all, we reduce the conflict points from 32 to 20, with the all-important crossing conflicts reduced from 16 down to 2. This is just an example of the types of designs that are available to replace our antiquated conventional signalized intersections.

You’ve given me fifteen minutes of your time and I greatly appreciate it, but I have a favor to ask of you. I need you to tell your friends about this; I need you to tell your colleagues about this; I need you to tell your elected officials about this. We can’t wait any longer to embrace these alternative designs. People are dying, our youth are dying, and we need to fix it. I can stand up here and talk until my voice goes hoarse about why we should build these and what is at stake, but I can’t change the world without your help. I want my children, all of our children, to become joyous sources of traffic: driving to school or their summer job, taking their dates to prom, or going on a road trip. I’m anguished over the thought of them becoming an injury or fatality statistic, and I need your help to keep them safe. Thank you. Continue reading →