[staybailey]

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]

> 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]

> 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]

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]

I chose my words carefully. The quote in the article is in turn a quote from 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]

> 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."

And this is the problem. "Not statistically significant" means that the effect is very small. This is what you would expect if narrower lanes make driving more dangerous but then drivers compensate by being more careful; they approximately cancel each other out. The author is making much hay out of the possibility that drivers might be not only compensating but overcompensating for the reduction in safety, theoretically causing a (small) net increase in safety.

The fallacy of this is that intentional danger is not the only possible way to increase driver vigilance. As one example, we could promote self-driving cars. That allows us to capture a much larger safety increase because the increase doesn't have to be weighed down by the counterbalancing cost of having narrower lanes and less room to maneuver.

[dalke]

As a quibble, "not statistically significant" means "cannot tell if there was an effect, either positive or negative, because it's smaller than the noise." The only difference is that one can't use it to argue that it 'theoretically [caused] a (small) net increase in safety'.

You use the phrase "intentional danger". The flip side is that "illusory safety." A 12' lane may feel safer even though it actually isn't. But it feels like you stress the "intentional danger" part when the label is irrelevant - the questions are the number and severity of crashes, of human injury, of overall traffic capacity, etc. How one labels the emotional aspect of the driver's internal state isn't relevant to the outcomes.

Also, as secabeen pointed out, driver vigilance isn't the only concern. To add another one 12' of road surface is simply more expensive to repair, clean, and replace than 10' of surface.

Regarding self-driving cars - sure, but how does that change anything in the next 10-20 years of road design? The underlying factors won't change unless a large percentage of vehicles are self-driving. You might as well argue that enforcing a 10mph speed limit would be safer as well, as another example of a solution which, even though correct should it occur, won't affect anyone's planning now.

[secabeen]

Right, but you're missing the author's point. Smaller lanes make the space feel more human-scale and friendly to pedestrians and bikers. Traffic engineers argue that larger lanes are safer. These studies show there is no evidence of that. Given that smaller lanes are more appealing, and have no measurable impact on safety, the trend towards larger lanes should be reversed, and smaller lanes implemented on new roads.