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There are many counter-intuitive effects in traffic engineering. Widening lanes has often been done in the name of safety, but the effect is that drivers feel s

There are many counter-intuitive effects in traffic engineering. Widening lanes has often been done in the name of safety, but the effect is that drivers feel safer driving faster, and the rates of deadly crashes rise. This suggests to me that to make roads safer, we might want to design them so that drivers feel they need to drive slower and more safely. Narrow the lanes where they are too wide, add roundabouts instead of multi-level exchanges, allow tighter curves. Especially useful for cities, since these changes would give back land for non-highway uses.

lostphilosopher 7y ago
Similar to a phenomenon in sports - more and better protective gear leading to more aggressive play leading to more injuries instead of the expected less.
- lostphilosopher 7y ago
  AKA "The Peltzman Effect" - https://en.wikipedia.org/wiki/Risk_compensation#Peltzman_effect https://en.wikipedia.org/wiki/Risk_compensation#Peltzman_eff... Was too busy to cite sources at the time, but for posterity: https://www.nytimes.com/2017/01/06/opinion/the-dangers-of-safety-equipment.html https://www.nytimes.com/2017/01/06/opinion/the-dangers-of-sa... https://www.usatoday.com/story/sports/ncaaf/2013/07/30/concussions-college-football-nfl-guardian-caps/2601063/ https://www.usatoday.com/story/sports/ncaaf/2013/07/30/concu... https://sports.cbslocal.com/2015/07/03/lemco-why-football-needs-less-pads/ https://sports.cbslocal.com/2015/07/03/lemco-why-football-ne...
birdman3131 7y ago
I don't know how many time roundabouts and gps have caused near dangerous split attention that just does not happen with normal stoplights. They may be better for local traffic but for anybody from out of town they are worse.
- notatoad 7y ago
  >Roundabouts reduced injury crashes by 75 percent at intersections where stop signs or signals were previously used for traffic control, according to a study by the Insurance Institute for Highway Safety (IIHS) https://www.wsdot.wa.gov/Safety/roundabouts/benefits.htm https://www.wsdot.wa.gov/Safety/roundabouts/benefits.htm
- jessaustin 7y ago
  Accidents happen at intersections because many drivers are not good at making themselves aware of traffic approaching from multiple directions. At a roundabout drivers only need to look in one direction. They are strictly better than traffic lights for all drivers except those who are not experienced with roundabouts. Those drivers should familiarize themselves with roundabouts.
  - davidgay 7y ago
    Of course it's always possible to screw up a good thing: the intersection next to our house has been replaced by a roundabout with a 2-way stop sign. To make it worse, you can really only see the traffic coming from one of the other 2 directions when you are stopped. Result (people not being familiar with roundabouts doesn't help): people stop in the middle of going around the roundabout, and/or get honked at by the people coming from the 2 directions without stop signs. I'm sure an accident is coming soon :(
    - graywh 7y ago
      this sounds like some traffic calming measures that were recently installed near me just last year they are islands in the middle of the intersection, but not roundabouts, forcing cars to "swerve" to pass through they haven't worked as intended and are being re-evaluated
  - deleted 7y ago
    [deleted]
  - mikepurvis 7y ago
    Roundabouts are better for car-car crashes: there are fewer of them and they tend to be less serious— rear-enders where there's lots of crumple protection instead of T-bones like a conventional intersection. However, they're much, much worse for people walking and cycling.
wycy 7y ago
On the subject of counter-intuitive effects in traffic engineering, it also seems that adding more lanes to a highway actually makes traffic flow worse. Whenever a car changes lanes on a highway, a small traffic "shockwave" propagates backwards some distance, and more lanes -> more cars crossing more lanes -> more traffic. Anecdata: I live in DC with its notoriously bad traffic. The highways 395 and 495 have 4-6 lanes each and tons of traffic. On the other hand, the George Washington Parkway has just 2 lanes and carries a large volume of vehicles between 395 and 495, but has very little in the way of its own traffic (except in the event of an accident, of course). Traffic only really occurs on the GW at the junctions with 395 and 495 since the X95s don't have the capacity to receive all of the GW cars at-speed. Whereas the X95s will get random backups for seemingly no reason, and at all hours of the day, backups on the GW generally only occur at the ends.
- Retra 7y ago
  If a lane is shut down due to an accident, it is better to have five spares though.
- rpiguy 7y ago
  For highly congested areas the increase in the number of lanes is done to accommodate the number of cars on a given route (optimize for capacity). If you can physically fit four times as many cars on a route, but it results in only being able to move at 1/3 normal speed you are still moving more cars over time than a two lane road.
- linuxftw 7y ago
  It's not random, it's poorly engineered entrance and exit ramps. In order to maintain traffic flow, cars need to be able to increase to traffic speeds on on-ramps and decrease on off-ramps. Much have the beltway system put entrance and exit ramps where they definitely don't belong. Thoroughfares for in-city traffic also don't exist, the interstate has taken that role. To compound the problem, often times entrance and exit ramps are the same piece of pavement.
- JamesBarney 7y ago
  I think a lot of the counter-intuitive effects in traffic engineering are due to traffic arbitrage. If you make a path much better more people will take it until it's as bad as all the alternate routes.
BethGagaShaggy 7y ago
More like unintuitive rather than counterintuitive, because the prediction doesn't fail because wider lanes are more dangerous per se, but because of the behavioral response of the drivers. Which can actually be considered "intuitive" to someone who is used to trying to model such things.
Sharlin 7y ago
> This suggests to me that to make roads safer, we might want to design them so that drivers feel they need to drive slower and more safely. Yes: https://en.wikipedia.org/wiki/Traffic_calming https://en.wikipedia.org/wiki/Traffic_calming
- hinkley 7y ago
  I read an article long ago about incorporating optical illusions into traffic calming. Things like the shape of ditches and the placement of trees on highways and parkways to make the shoulders look narrower than they really are. Making the road appear more dangerous than it really is makes people slow down and pay attention, without the uptick in danger of an actual hazard.
  - LoSboccacc 7y ago
    "Let's train people to ignore danger" what we need is red camera* at every light and speed trap at every road, only the fear of enforcement keep people honest *minus the whole shorten yellows for profit, of course
    - arebours 7y ago
      Surely we could more or less eliminate all kind of law violations by total control. But I don't think this is what we want as a society.
      - LoSboccacc 7y ago
        I'm not arguing about every single law, only those that have impact on the leading cause of death beyond health issues in the civilized world but ok, nice slippery slope, I guess.
        arebours 7y ago
        Let my rephrase it in a better way I hope. I'm not trying to say that once we introduce methods to fully detect some types of law infractions it will inevitably lead to a totalitarian regime. But I believe some leeway is necessary for people to feel comfortable and somewhat free. I don't want to be punished every time I make a mistake. I think you can find some sweet spot between zero and total detection. And yeah, probably leaning towards the latter, in correlation with seriousness of a violation (optimal discoverability reaching zero rather means the law should be revoked, like jaywalking being penalized in my country imho). Also, how would you even know some law is optimal when no one violates it? I mean, we could put radars on every road and set the limit on 30 kph. The studies discussed in the article wouldn't be possible then. > I'm not arguing about every single law, only those that have impact on the leading cause of death beyond health issues in the civilized world Definitely speed is the factor. But what about other variables at play like road quality, intersections planning, lights, other traffic regulations? And if tweaking them actually lowered casualties equally well with better economical outcome? > only the fear of enforcement keep people honest As for a slippery slope. You vastly generalized your statement yourself tbh.
decebalus1 7y ago
> This suggests to me that to make roads safer, we might want to design them so that drivers feel they need to drive slower and more safely. Narrow the lanes where they are too wide anecdote about the opposite happening: There is the I90 tunnel in Seattle which I use very often. Some passages have 2 lanes, super narrow, no shoulder, nothing. Looks like this: https://goo.gl/maps/DzvhWZAoD5AkRVwA9 https://goo.gl/maps/DzvhWZAoD5AkRVwA9 You won't believe how fast people are going through that. Also, almost every time I get tailgated and I'm frankly amazed there hasn't been any major accidents in that tunnel considering how close people are driving (no following distance). Just yesterday I was tailgated by somebody on their phone (I could see the screen reflected in his face while he was texting). I don't want to imagine how an accident would look like in that tunnel. Honestly, a fender bender can become catastrophic before you realize what happened. Now if you mean 'narrowing' roads then probably yeah. Take a wide-ass lane and suddenly make it narrow (so that people using it every day are 'surprised' and they're more careful) and I could agree with you.
pedantsamaritan 7y ago
I enjoyed the survey that the book _Traffic_ by Tom Vanderbilt provided in the traffic engineering space. Many of the topics discussed in the comments I see here are discussed in the book.
bytematic 7y ago
Could put a big spike on the steering wheel
sisu2019 7y ago
Where I live in the south of Germany nearly every residential area has these artificially narrowed roads and it works a lot better than putting up a incongruent signs ie 30 on a 50 looking road. It also can look pretty nice when they use flower beds and trees for the narrowing: http://www.ibfunk.de/ibfunk-wAssets/img/leistungen/verkehrsanlagen/strassen/verkehrsberuhigte-strasse-unlinen-2.jpg http://www.ibfunk.de/ibfunk-wAssets/img/leistungen/verkehrsa...

lostphilosopher 7y ago

Similar to a phenomenon in sports - more and better protective gear leading to more aggressive play leading to more injuries instead of the expected less.

lostphilosopher 7y ago
AKA "The Peltzman Effect" - https://en.wikipedia.org/wiki/Risk_compensation#Peltzman_effect https://en.wikipedia.org/wiki/Risk_compensation#Peltzman_eff... Was too busy to cite sources at the time, but for posterity: https://www.nytimes.com/2017/01/06/opinion/the-dangers-of-safety-equipment.html https://www.nytimes.com/2017/01/06/opinion/the-dangers-of-sa... https://www.usatoday.com/story/sports/ncaaf/2013/07/30/concussions-college-football-nfl-guardian-caps/2601063/ https://www.usatoday.com/story/sports/ncaaf/2013/07/30/concu... https://sports.cbslocal.com/2015/07/03/lemco-why-football-needs-less-pads/ https://sports.cbslocal.com/2015/07/03/lemco-why-football-ne...

birdman3131 7y ago

I don't know how many time roundabouts and gps have caused near dangerous split attention that just does not happen with normal stoplights. They may be better for local traffic but for anybody from out of town they are worse.

notatoad 7y ago
>Roundabouts reduced injury crashes by 75 percent at intersections where stop signs or signals were previously used for traffic control, according to a study by the Insurance Institute for Highway Safety (IIHS) https://www.wsdot.wa.gov/Safety/roundabouts/benefits.htm https://www.wsdot.wa.gov/Safety/roundabouts/benefits.htm
jessaustin 7y ago
Accidents happen at intersections because many drivers are not good at making themselves aware of traffic approaching from multiple directions. At a roundabout drivers only need to look in one direction. They are strictly better than traffic lights for all drivers except those who are not experienced with roundabouts. Those drivers should familiarize themselves with roundabouts.
- davidgay 7y ago
  Of course it's always possible to screw up a good thing: the intersection next to our house has been replaced by a roundabout with a 2-way stop sign. To make it worse, you can really only see the traffic coming from one of the other 2 directions when you are stopped. Result (people not being familiar with roundabouts doesn't help): people stop in the middle of going around the roundabout, and/or get honked at by the people coming from the 2 directions without stop signs. I'm sure an accident is coming soon :(
  - graywh 7y ago
    this sounds like some traffic calming measures that were recently installed near me just last year they are islands in the middle of the intersection, but not roundabouts, forcing cars to "swerve" to pass through they haven't worked as intended and are being re-evaluated
- deleted 7y ago
  [deleted]
- mikepurvis 7y ago
  Roundabouts are better for car-car crashes: there are fewer of them and they tend to be less serious— rear-enders where there's lots of crumple protection instead of T-bones like a conventional intersection. However, they're much, much worse for people walking and cycling.

wycy 7y ago

On the subject of counter-intuitive effects in traffic engineering, it also seems that adding more lanes to a highway actually makes traffic flow worse. Whenever a car changes lanes on a highway, a small traffic "shockwave" propagates backwards some distance, and more lanes -> more cars crossing more lanes -> more traffic. Anecdata: I live in DC with its notoriously bad traffic. The highways 395 and 495 have 4-6 lanes each and tons of traffic. On the other hand, the George Washington Parkway has just 2 lanes and carries a large volume of vehicles between 395 and 495, but has very little in the way of its own traffic (except in the event of an accident, of course). Traffic only really occurs on the GW at the junctions with 395 and 495 since the X95s don't have the capacity to receive all of the GW cars at-speed. Whereas the X95s will get random backups for seemingly no reason, and at all hours of the day, backups on the GW generally only occur at the ends.

Retra 7y ago
If a lane is shut down due to an accident, it is better to have five spares though.
rpiguy 7y ago
For highly congested areas the increase in the number of lanes is done to accommodate the number of cars on a given route (optimize for capacity). If you can physically fit four times as many cars on a route, but it results in only being able to move at 1/3 normal speed you are still moving more cars over time than a two lane road.
linuxftw 7y ago
It's not random, it's poorly engineered entrance and exit ramps. In order to maintain traffic flow, cars need to be able to increase to traffic speeds on on-ramps and decrease on off-ramps. Much have the beltway system put entrance and exit ramps where they definitely don't belong. Thoroughfares for in-city traffic also don't exist, the interstate has taken that role. To compound the problem, often times entrance and exit ramps are the same piece of pavement.
JamesBarney 7y ago
I think a lot of the counter-intuitive effects in traffic engineering are due to traffic arbitrage. If you make a path much better more people will take it until it's as bad as all the alternate routes.

BethGagaShaggy 7y ago

More like unintuitive rather than counterintuitive, because the prediction doesn't fail because wider lanes are more dangerous per se, but because of the behavioral response of the drivers. Which can actually be considered "intuitive" to someone who is used to trying to model such things.

Sharlin 7y ago

> This suggests to me that to make roads safer, we might want to design them so that drivers feel they need to drive slower and more safely. Yes: https://en.wikipedia.org/wiki/Traffic_calming https://en.wikipedia.org/wiki/Traffic_calming

hinkley 7y ago
I read an article long ago about incorporating optical illusions into traffic calming. Things like the shape of ditches and the placement of trees on highways and parkways to make the shoulders look narrower than they really are. Making the road appear more dangerous than it really is makes people slow down and pay attention, without the uptick in danger of an actual hazard.
- LoSboccacc 7y ago
  "Let's train people to ignore danger" what we need is red camera* at every light and speed trap at every road, only the fear of enforcement keep people honest *minus the whole shorten yellows for profit, of course
  - arebours 7y ago
    Surely we could more or less eliminate all kind of law violations by total control. But I don't think this is what we want as a society.
    - LoSboccacc 7y ago
      I'm not arguing about every single law, only those that have impact on the leading cause of death beyond health issues in the civilized world but ok, nice slippery slope, I guess.
      - arebours 7y ago
        Let my rephrase it in a better way I hope. I'm not trying to say that once we introduce methods to fully detect some types of law infractions it will inevitably lead to a totalitarian regime. But I believe some leeway is necessary for people to feel comfortable and somewhat free. I don't want to be punished every time I make a mistake. I think you can find some sweet spot between zero and total detection. And yeah, probably leaning towards the latter, in correlation with seriousness of a violation (optimal discoverability reaching zero rather means the law should be revoked, like jaywalking being penalized in my country imho). Also, how would you even know some law is optimal when no one violates it? I mean, we could put radars on every road and set the limit on 30 kph. The studies discussed in the article wouldn't be possible then. > I'm not arguing about every single law, only those that have impact on the leading cause of death beyond health issues in the civilized world Definitely speed is the factor. But what about other variables at play like road quality, intersections planning, lights, other traffic regulations? And if tweaking them actually lowered casualties equally well with better economical outcome? > only the fear of enforcement keep people honest As for a slippery slope. You vastly generalized your statement yourself tbh.

decebalus1 7y ago

> This suggests to me that to make roads safer, we might want to design them so that drivers feel they need to drive slower and more safely. Narrow the lanes where they are too wide anecdote about the opposite happening: There is the I90 tunnel in Seattle which I use very often. Some passages have 2 lanes, super narrow, no shoulder, nothing. Looks like this: https://goo.gl/maps/DzvhWZAoD5AkRVwA9 https://goo.gl/maps/DzvhWZAoD5AkRVwA9 You won't believe how fast people are going through that. Also, almost every time I get tailgated and I'm frankly amazed there hasn't been any major accidents in that tunnel considering how close people are driving (no following distance). Just yesterday I was tailgated by somebody on their phone (I could see the screen reflected in his face while he was texting). I don't want to imagine how an accident would look like in that tunnel. Honestly, a fender bender can become catastrophic before you realize what happened. Now if you mean 'narrowing' roads then probably yeah. Take a wide-ass lane and suddenly make it narrow (so that people using it every day are 'surprised' and they're more careful) and I could agree with you.

pedantsamaritan 7y ago

I enjoyed the survey that the book _Traffic_ by Tom Vanderbilt provided in the traffic engineering space. Many of the topics discussed in the comments I see here are discussed in the book.

bytematic 7y ago

Could put a big spike on the steering wheel

sisu2019 7y ago

Where I live in the south of Germany nearly every residential area has these artificially narrowed roads and it works a lot better than putting up a incongruent signs ie 30 on a 50 looking road. It also can look pretty nice when they use flower beds and trees for the narrowing: http://www.ibfunk.de/ibfunk-wAssets/img/leistungen/verkehrsanlagen/strassen/verkehrsberuhigte-strasse-unlinen-2.jpg http://www.ibfunk.de/ibfunk-wAssets/img/leistungen/verkehrsa...