On Bike Lanes, Road Widths, and Traffic Safety

There was an assertion made in one of the letters (signed by Louise Hainline, Norman Steisel, and Iris Weinshall in response to a recent New York Times editorial on cycling that caught my eye:

When new bike lanes force the same volume of cars and trucks into fewer and narrower traffic lanes, the potential for accidents between cars, trucks and pedestrians goes up rather than down. At Prospect Park West in Brooklyn, for instance, where a two-way bike lane was put in last summer, our eyewitness reports show collisions of one sort or another to be on pace to be triple the former annual rates.

The first point is that while the PPW conversion did take away one travel lane, the width of the existing lanes was not altered. So there may be fewer lanes, but they are not, as the letter argues, “narrower.” It may be that entire street feels narrower, which, as an emerging school of what I’ll call ‘behavioral traffic calming’ argues, is actually a good thing. Drivers, as I’ve quoted Ezra Hauer as saying, “adapt to the road they see.” They either do not see traffic signs or fail to read their meaning correctly. If they see a wide open, long boulevard, they will drive like this.

Even if the lanes were narrowed, as John LaPlante recently argued in the journal of the Institute for Transportation Engineers, “there is no significant crash difference between 10-, 11-, and 12-foot lanes on urban arterials where the speed limit is 45 mph (or less).” (a finding, he notes, that was unfortunately left out of AASHTO’s recent Highway Safety Manual).

And there’s something deeply suspicious about that “eyewitness reports” note; were they actually out there, day after day, meticulously logging conflicts and crashes (tellingly, they make no note of severity)? And why, if everything was so great with the street before, were they even doing these “before” counts? As the case of roundabouts shows, what people perceive as individual danger often does not translate at all to an increase in overall risk; in fact, it’s quite the opposite.

But let’s take that notion — that fewer and narrower lanes lead to more crashes. This is a staple of traffic engineering, and in fact it does have some validity — when applied to highway environments (which PPW at times unintentionally resembles). Even here, though, the effects are often not ‘statistically significant’ and ‘more complex than expected.’

But in non-highway environments, there’s all kind of evidence that reducing the number of lanes (a.k.a. the ‘road diet’) can have positive safety benefits. As the Federal Highway Administration has noted:

Road­ diets­ can­ offer­ benefits ­to­ both ­drivers ­and­ pedestrians… road diets may reduce vehicles speeds and vehicle interactions, which could potentially reduce the number and severity of vehicle-to-vehicle crashes. Road diets can also help pedestrians by creating fewer lanes of traffic to cross and by reducing vehicle speeds. A 2001 study found a reduction in pedestrian crashing risk when crossing two-and three-lane roads compared to roads with four or more lanes.

But what if one of those lanes your crossing is a bike lane? Surely that must make things less safe, no? More interactions in less space. In a forthcoming paper to be published in the Journal of Environmental Practice Norman Garrick and Wesley Marshall examined 24 California cities (12 with relatively low traffic fatality rates, 12 with relatively high rates). They found that the cities that had a higher bicycle usage had a better safety rate, not just for cyclists but all road users. They write:

Our results consistently show that, in terms of street network design, high intersection density appears to be related to much lower crash severities. Our street design data also contains strong indications of these trends; for example, the high biking cities tend to have more bike lanes, fewer traffic lanes, and more on-street parking. At the same time, large numbers of bicycle users might also help shift the overall dynamics of the street environment – perhaps by lowering vehicle speeds but also by increasing driver awareness – toward a safer and more sustainable transportation system for all road users.

And as Eric Dumbaugh, of the University of Texas A&M, notes, “most recent research reports that wider lanes on urban streets have little or no safety benefit, at least to the extent that safety is measured in terms of empirical observations of crash incidence” (e.g., Potts, I.B., Harwood, D.F., & Richard, K.R. (2007). Relationship of Lane Width to Safety for Urban and Suburban Arterials. Transportation Research Board 2007 Annual Meeting; Milton, J., & Mannering, F. (1998). The relationship among highway geometries, traffic-related elements and motor-vehicle accident frequencies. Transportation 25, 395–413; and so on).

But the authors of this letter are not trafficking in empirical evidence, even as they allege that the NYC DOT’s data “more puzzlement than enlightenment.” It’s unfortunate that this letter is signed by a former DOT commissioner, and an academic — who should both know that it is evidence and analysis, not vague “eyewitness” reports and random testimony, upon which good science, planning, and safety interventions are made.

And as always, curious to hear of more work either supporting or countering what I’ve said here.

This entry was posted on Thursday, December 23rd, 2010 at 12:47 pm and is filed under Bicycles, Cities, Cyclists, Drivers, Traffic Engineering, Traffic safety, Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

10 Responses to “On Bike Lanes, Road Widths, and Traffic Safety”

  1. Eric Fischer Says:

    The New York Police Department must collect statistics on collisions, mustn’t they? What do their numbers say?

  2. Marty Barfowitz Says:

    Keep in mind that Iris Weinshall is a former transportation commissioner who had no experience and little interest in actual transportation policy. Her oft-stated goal in the job was never anything more than “to keep the traffic moving.” Her unstated goal in the job was to make sure she never did anything that caused influential people to complain too much. When tough issues came up at public meetings, Weinshall always said: “I’m not a traffic engineer. I’ll take that back to the traffic engineers.” During Weinshall’s time in office, traffic engineers were the de facto policy-makers at NYC DOT.

    The progress and dynamism that we are currently seeing right now in New York City transportation policy is happening specifically because Weinshall is no longer there. She had to be removed from that job before this progress could take place. It is not surprising that she would assert these non-facts. Weinshall was never particularly interested in facts, analysis or policy even when she was DOT commissioner.

  3. Mimi Sheller Says:

    We make the same argument in “Challenging the King of the Road: Designing for Bicycles in American Cities” by Danish Visiting Scholar Jacob Bjerre Mikkelsen, which offers a new contraflow bike lane design for 34th St in West Philadelphia.

    The report is available as a free pdf download here:

    Please feel free to distribute the link!

  4. TownMouse Says:

    It’s entirely anecdotal but I’ve heard from two separate people in two separate cities (Dublin & London) that bike hire schemes contribute to road safety because people on hire bikes could be relied on to do absolutely anything at any time so the car drivers have to be alert at all times.

  5. Crusty Says:

    Ms Weinshall’s group was able to muster about 15 people at a demonstration they called last October. Several hundred bike lane supports showed up for the counter-demonstration. I suspect that the traction this small group has gotten with the press has more to do with the fact that she is the wife of Senator Schumer that the one time commissioner of transportation.

  6. Barb Chamberlain Says:

    Do any of these studies (or others) break out the data to examine differences in collision rates on streets that are designated truck routes vs. ones that aren’t? I’d like to see analysis of how narrower lanes accommodate large trucks with wide side-view mirrors alongside other users.


  7. djangosChef Says:

    That’s the nice thing about propaganda: facts are immaterial. Just float the idea (or impression, really) and a certain number of people will latch onto it. Culture wars are always like this. I hope they publish(ed) someone NYer’s rational response to that letter.

  8. Louise Hainline Says:

    This is a longer than usual post, but it is a serious response to the Vanderbilt piece which only recently came to our attention.
    Tom Vanderbilt raises some interesting points in his December 23rd blog entry, “On Bike Lanes, Road Widths, and Traffic Safety,” the main thrust of which is to question our assertion, in a very brief letter to the New York Times, that “When new bike lanes force the same volume of cars and trucks into fewer and narrower traffic lanes, the potential for accidents between cars, trucks and pedestrians goes up rather than down.”

    We do not dispute Vanderbilt’s argument that lane narrowing and removal (‘road diets’) and increases in bike traffic —in general— may not increase the incident of accidents in some circumstances. But we do maintain that in the specific case of the Prospect Park West (PPW) bike lane, as currently configured, accidents have gone up rather than down.

    There are reasons why the specific case of PPW is not typical of locations where accidents have not increased due to lane narrowings, closures, and increased biking:

    (1) PPW is not simply an arterial roadway between intersecting streets (as is the adjacent roadway inside Prospect Park, which, we have argued, would be a more appropriate location for a two-way bike lane). Rather, PPW borders high-density residential blocks—with a school and elder-care facility (on one side of the street) and entrances to Prospect Park (on the other). This means that on a less-than-one-mile stretch of roadway, thousands of residents and park-goers are continuously entering or exiting school buses, wheel-chair vans, taxis, or driveways, while dozens of Fresh Direct, UPS, Fedex, USPS trucks, moving vans, and other delivery vehicles are also blocking one of the two remaining traffic lanes. This requires that drivers in the blocked lane continuously shift into a single more-heavily-used traffic lane to avoid the blockage. And since this single lane is now narrower on a significant stretch of PPW, if not the entire street (as our measurements, pace Vanderbilt’s assertion to the contrary, clearly show), there is less margin to avoid car doors opening, drivers or passengers squeezing into their vehicles, parents lifting babies from their car-seats, cars edging into or out of parking spots, or side view mirrors extending from vehicles. These circumstances, rather than producing a “calming feeling,” are more likely to produce irritated impatience, at best.

    (2) Pedestrians may in general be safer if they cross fewer lanes of traffic, even if one of those lanes carries bicyclists. But in the case of PPW, when the now-narrower parking lane has been moved in-between the traffic lanes and the bicycle lane, cars block the pedestrians’ view of the silently oncoming bikers (particularly if said pedestrians are short or stooped, as the young, elderly, or wheel-chair-bound often are). This condition is exacerbated when the bikers fail to stop when pedestrians are crossing the lane with a “walk” light, as is too-often the case, or are speeding (ditto). Most importantly, perhaps, is the fact that rather than a one-way flow of bikes (to match the one-way flow of cars and trucks to which pedestrians are habituated), the bikes are coming from both directions, called “contra-flow”; because, among other reasons, contra-flow makes bikes move counter to the traffic rules, according to the 1997 NYC Bicycle Master Plan (ref 1), this design should be used only under very special circumstances. In addition to the option of moving the lane onto the adjacent roadway inside the park, making the PPW bike-lane one-way is the other proposal we have made as members of “Neighbors for Better Bike Lanes.”

    (1) Vanderbilt’s basic argument relies on the perception of increased safety that roadway users (drivers, bikers, and pedestrians) may have when more drivers and riders are using fewer and narrower lanes, because their awareness of other roadway users is heightened. But this perception of increased safety is not what users of PPW have experienced. In a self-selected survey of over 3,000 Brooklynites conducted by Councilmembers Lander and Levin, most people—bikers were the only exception—reported feeling less safe after the bike lane was installed (Ref. 2).

    (2) Vanderbilt questions the validity of “eye-witness reports” of collisions, notes that there is no control for the severity of these accidents, and wonders why “before” observations were made if there was no concern over safety issues prior to the installation of the bike lane. While it is quite true that the available data do not allow us to control for the severity of accidents, the observations reported to us by eye-witnesses after the installation of the lane are the only data that we or anyone else has to go on. We have never called them “statistics”, but they are valid field-report cases. The pre-lane data are those reported by the NYS DMV from NYC Police Department records. Despite our Freedom of Information requests to NYC DOT for post-lane safety data, none have been made available. The pre-lane data show PPW to be the safest street in that part of Brooklyn; no fatalities were reported for a decade or more, but official data for 2010 are not yet available. In just six months since the lane was installed, however, there have been well over a dozen reported accidents of varying types (car-to-car, biker-to-pedestrian, car-to-biker) and a fair number of biker-pedestrian accidents that have never been part of official figures (though the Transportation Committee of the NY City Council is considering asking for them to be required), so determining if these have increased will be a challenge.

    (3) A further safety risk is due to decreased accessibility for emergency vehicles due to lane blockages. This situation is exacerbated during snow events such as we have experienced in recent weeks. We would be happy to supply photographs taken after the recent blizzards to show how plowed and unplowed snowdrifts worsen the problems we mention above.

    Vanderbilt closes by lamenting the fact that “unfortunate[ly]…this letter is signed by a former DOT commissioner, and an academic — who should both know that it is evidence and analysis, not vague ‘eyewitness’ reports and random testimony, upon which good science, planning, and safety interventions are made.” To which we can only say that Vanderbilt’s own use of the studies he cites to support his case (“there is no significant crash difference between 10-, 11-, and 12-foot lanes on urban arterials where the speed limit is 45 mph [or less]”; “most recent research reports that wider lanes on urban streets have little or no safety benefit, at least to the extent that safety is measured in terms of empirical observations of crash incidence”, et al.) reveals an inability to distinguish between correlation and causation and a failure to understand that scientific reasoning does not permit acceptance of the null hypothesis in support of a conclusion. In his arguments, Vanderbilt also boldly generalizes conclusions from studies of road configurations (freeways, rural and small urban roads) quite different from those on PPW. However, the traffic engineering literature (including some studies cited by Vanderbilt) makes it clear that varied dynamics for different road environments can markedly influence the results from redesigns intended to increase safety. None of the studies cited were done in conditions like those we describe above for PPW. This leads to Vanderbilt’s failure to account for the operationally significant differences between the studies he cites and the PPW-specific situation.

    Vanderbilt’s concluding assertion that we “are not trafficking in empirical evidence, even as [we] allege that the NYC DOT’s data ‘[produce] more puzzlement than enlightenment’” is similarly planted in quicksand. DOT has failed to provide any sufficient detailed data to document their assertion that traffic speeds on PPW prior to the implementation of the bike lane were unacceptably high, that speeds and accidents since implementation of the bike lane have been significantly reduced, or that bicycle usage (particularly of commuters) has increased to the levels claimed. NBBL’s data, on the other hand (which we have offered to share with the DOT) clearly support assertions we have made, for example, that video-taped counts of bike-lane ridership for the same days DOT purports to have measured are only about half of what they have claimed (Ref 3).

    Louise Hainline, Norman Steisel, and Iris Weinshall

    Ref 1: New York City Bicycle Master Plan (1997), p. 52,
    Ref 2: Levin/Lander “PPW Results Final Release,” p. 18,
    Ref 3: Norman Steisel to Deputy Mayors Harris, Steel, and Goldsmith, 12-14-10.

  9. Marty Barfowitz Says:

    Wow. I love that Iris Weinshall is trotting out the 1997 Bike Master Plan, a plan that she did about as little as possible to move forward during her time as DOT commissioner…

  10. Tyler Says:

    I find it HILARIOUS that Ms. Winshall doesn’t see any irony here… How did she react when folks demanded traffic data from her?! And when the DOT provides data, it’s immediately called falsified and exaggerated.


    By the way, Dr. Hainline, the visibility issue is PATENTLY ABSURD! If you cross at crosswalks, there is no visibility issue! The view of the bike lane is completely unobstructed well before you enter it. That’s what the buffer areas are for. Or are you talking about the 90 year old women jaywalking and crossing between parked cars?

    I ask you to truly take a moment to reflect on your HONEST motivations in this matter. Not the ones you’re representing publicly. My suspicion is that your authentic motivations are short-sighted, self-entitled and selfish. Guess what, your property value has most assuredly *improved* due to the addition of the bike lane.

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