Compelling Evidence That Wider Lanes Make City Streets More Dangerous

The rate of side impact crashes is lowest on urban streets with lanes about 10.5 feet wide — much narrower than the standard 12 feet. Graph: Dewan Karim

The “forgiving highway” approach to traffic engineering holds that wider is safer when it comes to street design. After decades of adherence to these standards, American cities are now criss-crossed by streets with 12-foot wide lanes. As Walkable City author Jeff Speck argued in CityLab last year, this is actually terrible for public safety and the pedestrian environment.

A new study reinforces the argument that cities need to reconsider lane widths and redesign streets accordingly. In a paper to be presented at the Canadian Institute of Traffic Engineers annual conference, author Dewan Masud Karim presents hard evidence that wider lanes increase risk on city streets.

Karim conducted a wide-ranging review of existing research as well as an examination of crash databases in two cities, taking into consideration 190 randomly selected intersections in Tokyo and 70 in Toronto.

Looking at the crash databases, Karim found that collision rates escalate as lane widths exceed about 10.5 feet.

Roads with the widest lanes — 12 feet or wider — were associated with greater crash rates and higher impact speeds. Karim also found that crash rates rise as lanes become narrower than about 10 feet, though this does not take impact speeds and crash severity into account. He concluded that there is a sweet spot for lane widths on city streets, between about 10 and 10.5 feet.

In Toronto, where traffic lanes are typically wider than in Tokyo, the average crash impact speed is also 34 percent higher, Karim found, suggesting that wider lanes not only result in more crashes but in more severe crashes.

The “inevitable statistical outcome” of the “wider-is-safer approach is loss of precious life, particularly by vulnerable citizens,” Karim concluded.

67 thoughts on Compelling Evidence That Wider Lanes Make City Streets More Dangerous

  1. The irony here is that the people who most often advocate for wider lanes on roadways are Fireman and Emergency Response Technicians. The very people who show up when there are horrific high speed crashes caused by wide suburban roads.

    This should provide every transportation planner with good enough evidence to provide push back to the outdated standards coming from the Firefighter governing groups that are used to justify these kinds of dangerous roads.

  2. Great study. Important results. I hope this becomes a big part of redesigning city streets.

  3. We often hear the excuse that “the firetrucks have to get through”. Why not just have smaller fire trucks? You don’t need a hook and ladder truck to fight fires in a suburban cul-de-sac.

  4. There are many ways to “traffic calm” streets that involve visual and psychological tools which are inexpensive and should be used at every opportunity:
    Narrower lanes (as noted in the article)
    Street trees – more and bigger is better-have proven to be calming.
    Roundabouts allow traffic to flow more slowly but steadily, doing away with the whole stop/start pattern that leads to increased emissions. By eliminating “T-bone” collisions, they’re safer too.
    People. Sidewalk activity, tables, pedestrians, interesting storefronts make drivers go slower.
    Shorter sight lines work well and can be created by putting islands (or roundabouts) or woonerfs with landscaping when curvy roads aren’t available.
    Changes in pavement treatments can make drivers feel that they’re not in a space designed exclusively for cars, so they’re more cautious, plus, you can reduce stormwater runoff by using permeable materials. .
    The list goes on, but you get the idea.

  5. 13-14″ lane width is more like highway-level spec territory (controlled access, expected speeds of 60-80 mph etc)

  6. Probably not that much. Most people tend to drive as fast as they feel safe doing so. The perceived risk is lower on a wider street so people drive faster (likely above the posted speed limit). Stated differently, if the speed limit on a street is 30 miles per hour but people feel safe driving at 40-45 miles per hour they will probably drive at the higher speed.

    This is not to say there aren’t good samaritans out there who drive the posted speed limit but I would think most of the crashes involved people who were going over that posted speed limit.

  7. That’s right. Extremely narrow lanes are less safe too. Figure 11 clearly shows what range of lane width is safer based on the safety analysis findings. This removes the “intuition or myth” based opinion that “wider lanes are safer”.

  8. Because the fire dept might NEED the larger trucks. Most towns can’t afford to keep two complete sets of vehicles just because some streets are narrow. Then also when the fire dept is paged out, they would have to know which set of trucks to use as a response vehicle.

  9. More than half of the drivers operate speed limit higher than official speed limit in North American cities. One of the root cause is wide lane along with unused or unwarranted lanes particularly in off-peak hours. Positive design elements such as narrower lanes will bring down slightly towards safer speed limit.

  10. Which costs us taxpayers more: building/maintaing/safety loss of wider roads or having the fire department buy different trucks? I’m sure there’s a balance somewhere.

  11. I know this is a change of subject but can someone explain to me how roundabouts are supposed to work for bicycles? The two roundabouts that I’ve attempted bicycling through here in Manhattan are completely bicycle unfriendly. There’s one on 110 and Central Park West and another on 59th and Central Park West and both are crazy, dangerous and frightening for bicyclists. Up on 110th bicycle riders usually just go on the sidewalk because the area is less busy with pedestrians and it just seems like the obvious safe thing to do. But on 59th St. it’s even more insane and I still haven’t figured out how bicycles are supposed to feel welcome there.

  12. It all comes back to how you design the lanes. A quick search for bike roundabouts in the Netherlands will show you how other countries have solved this problem already. The photo shows how providing dedicated, protected lanes & maintaining clear sight lines is key to a successful roundabout for both bicycle & auto traffic. Unfortunately in the US, bicycle infrastructure is an afterthought solved with paint rather than pavement.

  13. Research on the effect of posted speed limits, when there is no difference in design speed, has found that it changes median and 85th percentile travel speeds by less than 2 mph.

  14. Those aren’t even real roundabouts in the sense that traffic entering the circle is supposed to yield to traffic already in the circle. Leave it to NYC to stick traffic lights on roundabouts. That ends up being the worst of both worlds. A proper roundabout does not have traffic signals, nor does it need them. I’m not really sure exactly what NYC DOT had in mind here, but let’s just say they fucked up big time.

  15. That (“traffic entering the circle is supposed to yield to traffic already in the circle”) isn’t always the rule. As an example, that is the rule in the District of Columbia, whereas the reverse rule applies in Maryland (traffic already in the circle must yield to entering traffic). Now consider Chevy Chase Circle, which lies half in DC and half in Maryland.

    There, traffic signals are a necessity.

    I’m also wondering how pedestrians manage to cross traffic circles that aren’t signalized.

  16. In general, in most places in the world, the rule is traffic entering the circle yields to traffic in the circle. Of course, here in the US where roundabouts seem to be an alien concept we like to make up our own rules just to confuse drivers even more.

    As for pedestrians crossing traffic circles, why are signals needed? Pedestrians manage to cross many unsignalized conventional intersections with no trouble. If you don’t have enough gaps in traffic for people to cross a street, maybe you should look at reducing your traffic volume since that’s the real problem. The levels of traffic in Manhattan are insane by any standards. Failing that, consider grade separating motor vehicles and pedestrians at busy crossings. It’s safer for both. 75 years of experience has shown that signalized crossings don’t make things any safer for pedestrians. Pedestrians largely ignore them, and drivers can’t be depended upon to always stop on red either. Grade separation on the other hand takes human error out of the equation.

  17. Pedestrians manage to cross many unsignalized conventional intersections with no trouble. The notion that pedestrians always need a traffic signal to cross a street is ridiculous. If you don’t have enough natural gaps in traffic for people to cross a street, maybe you should look at reducing your traffic volume since that’s the real problem.

    I fully agree with that as a long-term perfect-world solution. That’s how it should be. But that’s often not how it is. What are pedestrians supposed to do then?

    Failing that, consider grade separating motor vehicles and pedestrians at busy crossings. It’s safer for both. 75 years of experience has shown that signalized crossings don’t make things any safer for pedestrians. Pedestrians largely ignore them, and drivers can’t be depended upon to always stop on red either. Grade separation on the other hand takes human error out of the equation.

    Grade separation also usually requires large amounts of space, which isn’t always available in cities.

    Remember here one benefit of a roundabout is to reduce the number of lanes a person must cross to one or two instead of an entire street.

    How? If I need to go from one side of a traffic circle to the other, obviously I’m going to have to cross two lanes of traffic, even if only one lane surrounds the circle (I have to cross it once on each side).

    Signalizing a roundabout totally defeats the main purpose of it, which is to keep traffic mostly in motion.

    It may be that there are higher purposes on this earth than keeping motor vehicles in motion.

    Also note most pedestrian deaths occur when hit by vehicles going at high speeds. By definition, you can’t speed through a roundabout at 50 mph but you can drive that fast through a regular intersection.

    It doesn’t take anywhere near 50 mph to kill a pedestrian.

  18. Implying, of course, that posted speed limits are pointless, and that people will travel at the design speed anyway.

    Excessively low speed limits + draconian enforcement = great hidden (and regressive) tax, however.

  19. It’s pretty obvious to me regular, signalized intersections just don’t work for pedestrians. At all. Most of the pedestrian deaths in NYC are people crossing in crosswalks with the light. It seems to me maybe we should at least try other ideas before passing judgement. Roundabouts are commonly used overseas, without traffic signals, and I never hear about any issues with people crossing. Occasionally pedestrian tunnels may be used on busier roundabouts , but in that case it’s probably only because any other solutions would be even worse for pedestrians. The point though is you don’t signalize roundabouts regardless of the reason. If you’re going to do that, then don’t bother with a roundabout at all. Just use a regular intersection.

    It may be that there are higher purposes on this earth than keeping motor vehicles in motion.

    Traffic signals adversely affect bikes and pedestrians far more than motor vehicles. That’s why I don’t like them. I personally couldn’t care less if it took an hour for a car to go 2 blocks in Manhattan but I do care if cyclists or pedestrians have to wait up to a minute at red lights every block or two. That seriously affects the utility of these modes. With a roundabout, crossing pedestrians have the right of way all the time, meaning motor vehicles must yield to them before entering the circle. That’s how it should be. While the same is also true of bikes, in general bikes can negotiate crowded crosswalks just slowing down a bit instead of stopping, then finding a gap between pedestrians. That’s much better than waiting at red light after red light (or more likely risking a ticket by ignoring red lights).

    It doesn’t take anywhere near 50 mph to kill a pedestrian.

    The point though is you can’t physically enter most roundabouts at more than about 20 mph. That’s generally acknowledged to be a relatively safe speed around pedestrians. I like the idea of safety enforced by infrastructure rather than by rules. The infrastructure is there all the time, like a traffic cop always on duty.

  20. When I lived in Boston many, many years ago, the newspaper polled a large number of drivers, and exactly 50% believed that the car entering the rotary had the right of way, while 50% believed the car already in the rotary had the right of way. Which is another way of saying TOTAL CHAOS.

  21. The theory is that higher speeds demand wider lanes, but in practice it works the other way — wider lanes demand higher speeds. So wide, wide streets will DEMAND that drivers speed on them. It’s a psychological thing — even well-intentioned, careful drivers speed, because the road is calling for it. Put up all the signs in the world and it doesn’t matter.

    Jeff Speck is a national hero and every employee in every city road department should be forced to memorize his book and pass a test on it. Even then, nothing good will happen until the codes (which most cities just copy blindly out of the the template) are changed.

  22. This just shows the abysmal level of driving training we have here in the US. This isn’t rocket science. It’s a roundabout. If someone driving can’t figure it out, maybe they don’t belong behind the wheel at all. Then again, three cars in the same area of a parking lot generally result in a traffic jam because nobody can figure out what to do, so I’m not surprised here. Sometimes I think getting behind the wheel lowers a person’s IQ by 50 points.

    Incidentally, when polled a few years ago a rather large number of drivers thought the default speed limit on NYC streets was 55 mph. I guess ignorance doesn’t extend only to roundabouts.

  23. One very, very important thing that is missing from this data is the crash severity. I’m not sure how this is measured generally, perhaps by collision speed or probability of injury or death as a result. I’m just guessing but I’d bet that the crash severity linearly increases with lane width, so that even though there are more crashes with very narrow streets they are less severe. Could be wrong though, I’d really like to see the data.

  24. Given the several myths stated here about modern roundabout design and operation, I suggest review of NCHRP Report 672, Roundabouts: An informational Guide (2010). It is free online as a PDF. Yes, yield at entry is a national requirement, but you simply need to look at the regulatory sign at entry for that information. As for lane widths, design doesn’t cause crashes, human behavior does. Over 93% is driver error. Signals are safe, but have 8 times the injury rate compared to roundabouts. Its human factors. As in most all design and safety relationships, context is critical. If you look at urban crashes on wider roads speed is a definite factor – but its behavior, choices, often poor ones. So I am more of a supporter of traffic calming techniques rather than a designed environment that creates actual restrictive conditions to cause caution and slowing. Overall, we should look at all our design tools, width only being one of them, we need to design in the context not rubber a stamp 12 foot or 10 foot. And I still don’t understand why in all this narrow lane discussion there is no acknowledgement that roads are not straight and vehicle make turns – which means off-set front to back wheels, especially medium and large trucks and buses of course.

  25. It’s pretty obvious to me regular, signalized intersections just don’t work for pedestrians. At all. Most of the pedestrian deaths in NYC are people crossing in crosswalks with the light.

    That isn’t because the intersections are signalized.

    The point though is you don’t signalize roundabouts regardless of the reason.

    I use signalized traffic circles regularly. If they were not signalized, they would be completely inaccessible to pedestrians.

    The point though is you can’t physically enter most roundabouts at more than about 20 mph.

    That’s not my experience at all.

    I like the idea of safety enforced by infrastructure rather than by rules. The infrastructure is there all the time, like a traffic cop always on duty.

    It’s also much more effective than rules. But I don’t think this plays out in the real world the way you think it does.

  26. I agree. There is a place for wide lanes – freeways, parkways and other access-controlled roads meant for high speed traffic, not city streets.

  27. It’s both behavior and design. I dare you not to speed on a wider street. I’m not blaming you or anyone else who drives fast or in an “unsafe manner” with that design. It’s a human condition to do so. This has been proven time and time again. And for the most part, the urban streets that they are discussing that have wider traffic lanes are in fact very straight with protected left and right turn lanes, but you are right additional study is needed.

    I believe the point of the article is to state that if “I am an engineer who has to design a street under a very tight timeline without much insight from political officials, only a few community meetings, and I have to have this done as soon as possible, and don’t have time or fee to run a statistical analysis. What is the best choice of lane width for this street based on safety and efficiency?” Use 10.5 instead of 12. That’s all.

    I’ve noticed that everyone always wants to do more, design more, make sure everything is perfect, but at the end of the day rarely want to pay for it (in both time and expense). Given that, this seems like compelling enough evidence for me (including my own anecdotal experience) to make policy recommending or mandating urban lanes to 10.5 ft.

  28. I think the 10.5 information is good and important to understand when making choices. Its just not the only factor. As an example, one of my middle east clients is using a wider outside lane where buses are, other lanes are narrow. I don’t know the effectiveness of this design, but the choice in interesting.

  29. Thanks for that clarification! It really helps to make it clear. I’ve also experienced the roundabouts in New Delhi… Of course that is a different brand of crazy, traffic wise. I don’t think I’ve ever experienced a around them out quite as you have described.

  30. Interesting discussion about roundabouts, thank you. It’s a bit beyond me since I almost never drive a car in New York City. It is interesting to notice however that there is actually a bicycle “lane” that leads directly into the roundabout at 59th St. If you are riding from the south on 8th ave…and if you actually are able to notice it at all, it disappears completely throwing you out into the craziness.

  31. Most of the pedestrian deaths in NYC are people crossing in crosswalks with the light.

    Perhaps because pedestrians predominantly cross at signalized intersections with the light. (Not many pedestrians are going to be killed crossing where few pedestrians cross in the first place.)

  32. http://safety.fhwa.dot.gov/intersection/roundabouts/fhwasa10023/transcript/audio_no_speaker/

    http://www.therecord.com/news-story/2586201-signalized-intersections-dangerous-places-for-pedestrians-statistics-show/

    http://www.mtjengineering.com/uploads/assets/pdf/can-modern-roundabouts-safely-accommodate-all-users.pdf

    One big problem here is virtually all intersections in NYC with heavy pedestrian traffic are signalized, and we really have few true roundabouts. We can’t draw any conclusions one way or another which is safer, at least in NYC, but the evidence elsewhere heavily favors roundabouts. It’s not just the geometry which makes them better. It’s the smoother traffic flow which makes things safer. When forward progress is in fits and starts, as is the case when all you have are traffic signals, the end result is eventually frustration and cutting corners just to gain a small bit of progress. It’s often the latter which kills people. That driver who turns into a crossing pedestrian, either because they didn’t look or choose to go anyway, is certainly 100% wrong. However, the situation on our streets is a perfect incubator for that sort of behavior. I’ll admit I even do it myself, on foot no less, when walking in places like Manhattan. After getting delayed waiting for cars time and again at each intersection, I might find myself just holding up my hand and walking in front of a car which might technically have the right-of-way. Sure, I only do this in front of slow moving vehicles, but the point is my prior frustration taking twice as long as I should to walk a given distance is what led to this admittedly selfish, asshat behavior. At least I’m only potentially putting myself at risk here. A driver experiencing similar frustration can easily kill people.

    The bottom line is NYC seriously needs to try other solutions. Roundabouts are not a good fit everywhere, but properly used they might led to better traffic flow (for everyone, not just motorists). That would mean less frustration, less cutting corners, fewer deaths. Even traffic engineers admit traffic signals are good sometimes for making traffic flow more orderly, but they rarely make things safer for anyone, least of all people outside of cars.

  33. Traffic on 64th yields to vehicles in the roundabout traffic on 188 does not. Not a ‘real’ roundabout by your definition above. Vehicles usually yield well enough to pedestrians in the marked crosswalks at that one, but if you want to cross from the boston market to the qdoba drivers aren’t great at yielding, nothing marked but that concrete median makes crossing there attractive. Don’t need a roundabout to have a median. The other one at 69th cars don’t yield as well. At 64 you have much more foot traffic, pedestrians are expected. In the residential area south of there? less so.

    Also has a huge physical footprint. 188 is 50 feet wide south of 69. The roundabout is 200 feet wide. There are buildings in the way at most intersections. What would be ideal if you were building greenfield and what you can do with the built environment you have are not necessarily the same thing.

  34. It’s as close to real roundabout as can be found in NYC at the moment, even if 188th Street does have the right-of-way.

    Realistically, on 69th Avenue not a whole lot of people cross 188th Street anyway. The median does make it easier to cross though. Also, traffic levels are reasonable most of the time. At the risk of repeating myself again when traffic is so heavy you have few natural gaps where people might cross then you have a traffic volume issue more than anything else. Fix that and a lot of other problems fix themselves. If you just stick in a traffic signal you essentially put a bandaid on a festering cut. The problem won’t get any better. It may indeed get worse. Little reason any NYC street anywhere should be so heavy with traffic the only time a person can cross is when a red light stops traffic. By implication this means a person crossing has to wait to cross, often for quite a while. That’s just wrong on so many levels.

  35. We could fix that regressive part — at least one country (Finland I think) indexes speeding taxes to income.

  36. Most of the pedestrian deaths in NYC are people crossing in crosswalks with the light.

    No. Only 27% of ped KSI are crossing at signalized intersections with the light. Deaths are probably lower than that. And many of those serious injuries the motor vehicle that hit the pedestrian was probably going less than 20 mph. You can only turn so fast (why deaths are probably lower – crossing against the light was 20% of KSI, but on average the crashes were 56% deadlier than with the light, cars going straight are going faster). The idea behind 20 mph being safe isn’t that it’s fine to hit people at that speed. It’s that it’s much much easier to avoid collisions than at 40 mph. If you’re focused on swerving around fixed obstacles I’m not sure it’s still slow enough for drivers to avoid collisions with pedestrians. Especially when you have cars turn left. The A pillar can easily block the view of something small, like a pedestrian or bicyclist.

    http://www.nyc.gov/html/dot/downloads/pdf/nyc_ped_safety_study_action_plan.pdf

    http://streets.mn/wp-content/uploads/2015/04/speed-visual-focus-diagram-426×500.jpg

  37. It’s worth noting that the real situation is even worse than those pictures indicate when you factor night driving into the equation. With the present HPS lights the spectrum basically totally kills peripheral vision. What you see at 15 mph (or really any speed) under HPS resembles the 30 mph picture. And HPS also kills depth perception, to the point street imperfections appear nearly flat until you’re nearly on top of them. It’s good large cities are switching or have already switched to LED streetlights. This will enhance safety quite a bit at night which is when a disproportionate number of pedestrian fatalities occur. In all honestly, although I rarely buy the excuse from a driver of “I didn’t see the person until it was too late”, I might well believe them if the crash occurred after dark. HPS lighting resulting in no peripheral vision, poor depth perception, and poor color rendering (i.e. a person might appear nearly indistinguishable from the street even wearing colors which might contrast under normal white light) could easily have that result.

  38. Here’s some food for thought—the theory for the last 50 years or so behind wide lanes and other factors which tend to increase driving speeds is to make roads more forgiving of human errors. To a great extent this works but only if you’re in a motor vehicle. It turns out the requirements for safety of other users may in fact require making roads less forgiving of human error, at least for those in the motor vehicle, to the point where if you drive faster than is safe for cyclists or pedestrians you can end up crashing and getting hurt. That’s part of the theory behind roundabouts. They create actual restrictive conditions which force drivers to slow down, or end they end up as part of the scenery if they don’t. When people have skin in the game, so to speak, they tend to be a lot more careful. If they’re not, the infrastructure tends to ensure that they may not have a chance to not be careful ever again.

    Human error is exactly why traffic signals have a much higher injury rate compared to roundabouts. There’s nothing enforcing a stop on red beyond the driver. If you decide to ignore the signal, or perhaps just mistake a red for green, the consequences can be deadly to you and others simply because nothing inherently limits your speed going through a regular intersection. Moreover, there are no physical obstacles in front of the driver which say “slow down”.

    A roundabout on the other had provides both visual cues to slow down, and real consequences if you don’t. We can’t get rid of human error but street design should mitigate the consequences of that error. The only difference here between the new and old philosophies is the old way seeks only to mitigate the consequences for those in the motor vehicle. The new way prioritizes those outside the motor vehicle, even if it’s at the expense of those inside. To me anyway this makes sense. If you drive or ride in a motor vehicle, you’ve bought into the risk associated with doing so. Someone on a bike or on foot hasn’t bought into that risk, and so should be protected from driver error, even if the end result is killing everyone in a motor vehicle to save a pedestrian or cyclist (obviously an extreme example which probably will rarely happen with good engineering but nonetheless an example of how our priorities should be).

  39. at night which is when a disproportionate number of pedestrian fatalities occur.

    There’s a time of day breakdown on page 24/25 in the link I gave above. (and again for convenience)

    http://www.nyc.gov/html/dot/downloads/pdf/nyc_ped_safety_study_action_plan.pdf

    Nationwide 46% of fatal pedestrian crashes were 8pm-4am. In NYC 9pm-6am was about 25%.

    Didn’t see the person until it was too late at night might often be true, but it means the driver was going too fast for conditions. It’s frequently not 25-35, whatever the speed limit might be. The next chart on that same page shows the share of pedestrian KSI crashes that are fatal by time period. 3-6pm ~7% of KSI crashes are fatal. Traffic is heavy, it slows cars down. 3-6am ~19% of KSI crashes are fatal. I’d wager that’s from all the speed demons that let loose after dark.

    At 30 I can’t see pedestrians entering the crosswalk at night until they’re right in front of me. At 15-20 I can see them on the corner with sodium lights, though I am looking for them. Where I’ve been on similar roads at night with LED lights I still can’t drive 30 and see someone trying to cross. Can’t always during the day either. But it is easier to see people at 15-20.

  40. I see it as slightly different. The roundabout can accommodate the design vehicle safety if it goes the correct speed (15-20). Some traffic calming techniques actually reduce the safety of the motorist and the design is marginal or less than accommodating. That’s what I don’t like because it shifts safety, creates a design hazard – like strong humps in the road requiring 5 mph – cop – judge, jury and executioner in the form of a unsafe condition. If you speed into a roundabout, yes, welcome to the center island. But, if you follow the signs everything is fine. Since traffic crashes are the most likely cause of death, I don’t think we should lean in the direction of hazard=calming. Its a fine line and will always be gray to some degree. Bumps are 5 mph and RBTs are 15-20, but that difference is very important at an intersection and is not a mid-block hazard.

  41. Well, I agree on the midblock hazards. Unless there’s a good reason to really slow traffic in between intersections to 5 or 10 mph, like maybe strong potential for children running into the street, any kind of midblock physical traffic calming is a misuse of the concept. We should restrict most physical traffic calming to intersections. And as I mentioned we should only calm traffic where it makes sense. If few or no people are crossing (and the reason is not due to unsafe crossing conditions but simply the fact little is within walking distance) then we really don’t need to slow traffic below safe driving speeds for that section of road.

    Incidentally, I’m not really a big fan of speed humps at all. When the slopes start to wear off they end up being a major hazard for cyclists, in that you might run into a very sharp increase in pavement height which can easily ruin wheels or throw you into the ground.

  42. Yes, an ill informed city park crew was going to install a asphalt bump on a downhill, 15 mph posted, to slow down bikes and cars doing 20 in the park. I asked them if they had thought about the little tykes, the roller blades, the elderly on bikes and other users of the road? Point being that context, purpose and consideration of all users is very important for a design feature. The bump did not happen. We try to physically manage those few with poor behavior and reduce the safety for everyone.

  43. But, if you follow the signs everything is fine.

    Speed bumps are often signed. Follow the signs and you’re fine there too.

  44. I remain uncomfortable with speed bumps even when signed and marked. As speed increases just a little bit they rapidly become more hazardous. They are hazardous at any speed to non-motorized modes lacking 4 wheels and 2 tons of protection. They are more challenging for any driver and are based on creating a design hazard not a curve in the road that any driver in any mode can easily deal with. They are more hazardous at night and wet weather. More hazardous to kids. There is no other reason for the bump other than “if you go to fast you will be punished without due-process. So slow down or risk physical punishment for your deed.”

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