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The theory is that people will drive more carefully if they perceive the roadway to be more dangerous. That is not the same as it actually being more dangerous.

The theory is that people will drive more carefully if they perceive the roadway to be more dangerous. That is not the same as it actually being more dangerous. Moreover, road safety is not fixed but rather dependent on the speed at which drivers drive on the road. Thus, if a roadway design causes drivers to drive slower on road B as opposed to road A, road B may be safer even if it would be less safe than road A if people drove the same speeds on both roadways. There is nothing particularly counter intuitive about this type of theory at all. Also perceived danger to oneself doesn't take into account the risk one poses to others. This issue of externalities is what makes these 12 foot lanes so dangerous. As noted in the article, if drivers are driving slower, they are far less likely to kill or seriously injure pedestrians. And since F = (.5)mv^2 this is exactly what we'd hypothesize. Pedestrians are a non-issue on the rural highways that the 12 foot lane and other state road design measures are based on. But in the middle of a dense city, higher speeds, even if they aren't any less safe for the drivers, are far less safe for pedestrians and cyclists, not to mention far more unpleasant to be around. It is this concept, more than anything else, that traffic engineers are so often obtuse to. And driver-less cars will have to be able to navigate the existing 10-foot lane roads anyways to be commercially viable, so I don't see how that is an issue.

AnthonyMouse 12y ago
> The theory is that people will drive more carefully if they perceive the roadway to be more dangerous. That is not the same as it actually being more dangerous. Without the expectation that people will compensate for it, making the lanes narrower does make it actually more dangerous. There will be less space between each vehicle and less space between the vehicle and pedestrians on the side of the road, which reduces the amount of space available to avoid an obstruction, the amount of reaction time available to avoid a collision, etc. > Also perceived danger to oneself doesn't take into account the risk one poses to others. That is a counterargument to your position. If drivers aren't bearing the full risk then an increase in risk should cause them to undercompensate, not overcompensate. > And driver-less cars will have to be able to navigate the existing 10-foot lane roads anyways to be commercially viable, so I don't see how that is an issue. It is possible to be less safe without being negligent and that difference is still measured in human lives.
- dalke 12y ago
  > making the lanes narrower does make it actually more dangerous. I think you're being downvoted in part because the linked article refutes your viewpoint. There's even a pullquote saying "States and counties believe that wider lanes are safer. And in this belief, they are dead wrong." Followed up in the text by "Or, to be more accurate, they are wrong, and thousands of Americans are dead." And "The lane widths in the analyses conducted were generally either not statistically significant or indicated that narrower lanes were associated with lower rather than higher crash frequencies."
  - wtallis 12y ago
    That's not a refutation, it's a contradiction. The evidence offered is not sufficient to actually prove the assertions. In particular, those crash frequencies need to be normalized against the reduced capacity in order to be a meaningful comparison. If narrowing the road decreases crashes because fewer people are using the road, you don't have a safer road, just less road, and you may have merely shifted the crashes to alternative routes. On the other hand, if narrowing the lanes makes people drive more carefully without significantly constricting flow, that's a real result that deserves to be stated clearly.
    - dalke 12y ago
      I chose my words carefully. The quote in the article is in turn a quote from http://trb.metapress.com/content/x7854w1160551331/ http://trb.metapress.com/content/x7854w1160551331/ . The article links to that publication. The abstract of that publication says: > This research investigated the relationship between lane width and safety for roadway segments and intersection approaches on urban and suburban arterials. The research found no general indication that the use of lanes narrower than 3.6 m (12 ft) on urban and suburban arterials increases crash frequencies. This finding suggests that geometric design policies should provide substantial flexibility for use of lane widths narrower than 3.6 m (12 ft). The inconsistent results suggested increased crash frequencies with narrower lanes in three specific design situations. Narrower lanes should be used cautiously in these three situations unless local experience indicates otherwise. It it turn builds on, for example, results by Hauer, et al, Strathman et al. which appear. You then raised another objection, which is, I believe, that a 10' lane causes people to use alternate routes because of decreased capacity on those lanes, so there are simply fewer people on the 10' lane roads to cause accidents. This may well be. It's a subtle network effect that is hard to analyze, and not covered in this article. (The article does comment that capacity is unchanged, but I think its literature citations are weak. It quotes Petritsch who in turn quotes a summary of an unpublished literature search.) However, your objection is not what was refutated. AnthonyMouse proposes that narrowing lanes lead to a higher accident rate since it "reduces the amount of space available to avoid an obstruction, the amount of reaction time available to avoid a collision, etc." While true for country roads, those above papers show that the same correlation can not be identified on city roads. Now, what I know is only from this article, and it may be that the author cherry-picked the few papers which show that the 'reaction time' hypothesis is unsupported by the evidence. But "refute" means "to deny the accuracy or truth of", and certainly the article refuted that hypothesis.

AnthonyMouse 12y ago

> The theory is that people will drive more carefully if they perceive the roadway to be more dangerous. That is not the same as it actually being more dangerous. Without the expectation that people will compensate for it, making the lanes narrower does make it actually more dangerous. There will be less space between each vehicle and less space between the vehicle and pedestrians on the side of the road, which reduces the amount of space available to avoid an obstruction, the amount of reaction time available to avoid a collision, etc. > Also perceived danger to oneself doesn't take into account the risk one poses to others. That is a counterargument to your position. If drivers aren't bearing the full risk then an increase in risk should cause them to undercompensate, not overcompensate. > And driver-less cars will have to be able to navigate the existing 10-foot lane roads anyways to be commercially viable, so I don't see how that is an issue. It is possible to be less safe without being negligent and that difference is still measured in human lives.

dalke 12y ago
> making the lanes narrower does make it actually more dangerous. I think you're being downvoted in part because the linked article refutes your viewpoint. There's even a pullquote saying "States and counties believe that wider lanes are safer. And in this belief, they are dead wrong." Followed up in the text by "Or, to be more accurate, they are wrong, and thousands of Americans are dead." And "The lane widths in the analyses conducted were generally either not statistically significant or indicated that narrower lanes were associated with lower rather than higher crash frequencies."
- wtallis 12y ago
  That's not a refutation, it's a contradiction. The evidence offered is not sufficient to actually prove the assertions. In particular, those crash frequencies need to be normalized against the reduced capacity in order to be a meaningful comparison. If narrowing the road decreases crashes because fewer people are using the road, you don't have a safer road, just less road, and you may have merely shifted the crashes to alternative routes. On the other hand, if narrowing the lanes makes people drive more carefully without significantly constricting flow, that's a real result that deserves to be stated clearly.
  - dalke 12y ago
    I chose my words carefully. The quote in the article is in turn a quote from http://trb.metapress.com/content/x7854w1160551331/ http://trb.metapress.com/content/x7854w1160551331/ . The article links to that publication. The abstract of that publication says: > This research investigated the relationship between lane width and safety for roadway segments and intersection approaches on urban and suburban arterials. The research found no general indication that the use of lanes narrower than 3.6 m (12 ft) on urban and suburban arterials increases crash frequencies. This finding suggests that geometric design policies should provide substantial flexibility for use of lane widths narrower than 3.6 m (12 ft). The inconsistent results suggested increased crash frequencies with narrower lanes in three specific design situations. Narrower lanes should be used cautiously in these three situations unless local experience indicates otherwise. It it turn builds on, for example, results by Hauer, et al, Strathman et al. which appear. You then raised another objection, which is, I believe, that a 10' lane causes people to use alternate routes because of decreased capacity on those lanes, so there are simply fewer people on the 10' lane roads to cause accidents. This may well be. It's a subtle network effect that is hard to analyze, and not covered in this article. (The article does comment that capacity is unchanged, but I think its literature citations are weak. It quotes Petritsch who in turn quotes a summary of an unpublished literature search.) However, your objection is not what was refutated. AnthonyMouse proposes that narrowing lanes lead to a higher accident rate since it "reduces the amount of space available to avoid an obstruction, the amount of reaction time available to avoid a collision, etc." While true for country roads, those above papers show that the same correlation can not be identified on city roads. Now, what I know is only from this article, and it may be that the author cherry-picked the few papers which show that the 'reaction time' hypothesis is unsupported by the evidence. But "refute" means "to deny the accuracy or truth of", and certainly the article refuted that hypothesis.