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This is a fine analysis if you imagine that every road only ever has cars on it. But this is not the reality, and speed of cars has a huge impact on the fatalit

• bitwize 9y ago
  The article was talking about 55 mph speed limits on freeways -- highways restricted to vehicular traffic only. Roads likely to be used by pedestrians or cyclists will have a limit of 25 to 45 mph.
  • CalChris 9y ago
    That is not the case. The article says Every year, traffic engineers review the speed limit on thousands of stretches of road and highway.
  • Nition 9y ago
    Petrol consumption is often best in cars at around 45mph (70km/h), so one effect of increasing highway speed limits not mentioned would be worse fuel economy.
    • ZantaWB 9y ago
      This was mentioned in the article as the main reason for the legacy 55mph limit imposed after the Saudi oil embargo.
      • Nition 9y ago
        Oops, I see that now. My fault for only reading the first section of the article.
    • deleted 9y ago
      [deleted]
    • coredog64 9y ago
      Spark ignition engines suffer from pumping losses when throttled. So it is a pretty broad generalization to throw that number out. Fuel economy will depend on rolling resistance, gearing, and aerodynamics.
    • tropo 9y ago
      That number comes from a time of 3-speed transmissions and non-aerodynamic bodies. I heard better numbers back when 5-speed was becoming common, but now we're seeing 8-speed and 9-speed and CVT. It's probably around 65mph now.
      • Nition 9y ago
        I've heard 70km/h elsewhere, but the only personal data I have is I used to drive a 2002 5-speed manual VW Golf Mk IV, the 2L petrol version, and that had a fuel economy display on it plus a nice chart of economy per gear in the owner's manual. The book similarly said best would be at around 70km/h (~45mph) in 5th gear, and I confirmed that was true in my own tests. The 6-speed GTI was charted in the owner's manual as well and its best economy was shown as a little faster, in its extra 6th gear.
      • YSFEJ4SWJUVU6 9y ago
        Aerodynamic resistance (“drag”) doesn't care about your transmission. The sweet spot is even lower with electric cars (especially with all the peripheral devices turned off). However, a modern mid-sized car with an efficient engine gets 40 MPG or more at 75 MPH, while a gas guzzler won't get such mileage at any speed.
      • dagw 9y ago
        Own a 2014 6-speed petrol VW and according to the manual the optimal speed for max mileage is around 70-75 km/h
  • zanny 9y ago
    The main street in the town I live in (population 4500, not that big) has a posted speed limit of 25mph. Until last year, the road was in such bad repair that most traffic only averaged around 30. Then they repaved the road, and despite it still being 2 lane with parking on both sides, tons of merge traffic without any lights (from stopsigns) and being next to the town park with a ton of foot traffic, I'd estimate the average speed on that road is now 45-50mph. Precisely because its straight, freshly paved, and nobody wants to slow down the traffic when its smooth sailing with no lights. To try to counteract this, those signs that tell you your speed were put up that blink when you are going over the limit. They were promptly ignored. So really I'm just trying to reiterate that what the article says is absolutely true - people will drive what they feel comfortable going, not what the posted speed limit says. In practice, the risks are there, but nowadays everyone knows to avoid main street for pedestrian crossing because its approaching highway speeds now. But on very congested roads like our main street (this being a 250 year old town, where there is no traffic shaping planned, so all through traffic goes down the road that also has the most foot traffic) you aren't going to have an easy answer, because slowing down traffic can be just as dangerous when its bumper to bumper for the ~5 mile long road through town and drivers will go mad being forced back to 25mph combined with the immense traffic bottleneck it would reintroduce (the main reason they fast tracked paving the road in the first place - traffic would back up onto the nearby highway offramp because of how bad main street traffic is). I think the reality is that busy streets are just never safe for pedestrians (or bikes, etc). That is why you invest in crosswalks meant to funnel people across them all at once, in centralized places, where traffic is already forced to stop. And if you really care, you get the cars out of downtown entirely.
  • Brendinooo 9y ago
    In Pennsylvania, I once rode my bike on a 55-mph, four-lane divided highway that is designated as an official bike route[0]. Traffic was sparse on the road so it objectively probably wasn't too bad, but it wasn't a pleasant experience to have cars rush by you at those speeds. [0]: http://bikepa.com/routes/index.htm http://bikepa.com/routes/index.htm
  • CalRobert 9y ago
    Source? I have cycled routinely on roads with speed limits greater than this. The first that comes to mind is Madison Ave in Sacramento (often 50mph+). For that matter I used to have a commute that took me on a brief stretch of I-5 in San Diego - that was hair-raising, to say the least. It's legal there due to lack of other options.
• ksenzee 9y ago
  But the point of the article is that changing speed limits doesn't change the speed of cars. If we want to slow cars down, we need to use traffic calming mechanisms that work. Speed limits don't.
  • TulliusCicero 9y ago
    Speed limits can act as a target, though. It'd be a little weird to have a 'realistic' speed limit of 35 mph, and then introduce traffic calming measures designed to slow people down to way lower than that, no?
    • rsfern 9y ago
      I think the idea is to use traffic calming methods to change the 'realistic' speed limit from 35 mph to 25 mph, and then post signs for 25 mph.
    • zanny 9y ago
      The speed limit should reflect the reality of the road. No, you shouldn't go around tomorrow updating all your speed limits to 85% percentile graded and then try to redraw the roadways to traffic shape to desired speeds. You would do the latter first, then update your signs. Except in most places, neither is happening. People are driving dramatically over the speed limit because that is the natural speed of the road, and no attempts to change the actual speeds of traffic are happening because they cost money. So people get to die for the multitude of reasons the article outlines because of political deadlock.
    • zaphar 9y ago
      The point of the article is that for 85% of the people driving on the road the speed limit most emphatically does not act as a target. If it did then modifying the limit would be a useful knob you could turn. Since it isn't all it does if give the non-automotive traffic a false sense of security regarding how fast traffic might be coming at them.
  • joering2 9y ago
    But why do you want to adjust all the roads in the country where maximum speed ever is 90mph, at least in the USA? Just pass the law to limit cars from driving faster than that, and problem solved! It always amazes me how cars commercials show awesome dashboards with 250 mph speedos, perfectly knowing there is no single road that you can lawfully go that fast. Heck, it probably won't cost much more than a thumb drive to stick into your car computer port to update speed limits built in.
• drtz 9y ago
  I had the same thought as I read the article. In the author's defense there was a single sentence towards the end of the article that mentioned effective ways of lowering driving speeds. More discussion of those methods would've been a nice addition.
• jdavis703 9y ago
  I think the debate on speed is about limited-access freeways, where no bikes or pedestrians should be, and where other vehicles won't be doing things like making u-turns, parallel parking etc. As someone who uses basically all the modes of travel that a complete street allows, I'm all for lowering the speed limits (especially through road design, not just a speed limit sign). But a highway is completely different, the only thing you have to worry about are other cars.
  • mark-r 9y ago
    In the context of the article, it would be about any state-controlled roads. Many of those roads would not be limited-access freeways. Given the stated stated observation that speed limit signs have very little correlation with driver behavior, the only way to significantly impact road speeds is through road design.
    • mirimir 9y ago
      That's true. So yes, road design. I vaguely recall that the US interstate system was generally designed for 150-200 km/hr.
• civilian 9y ago
  I agree, let's fucking reduce pedestrian deaths! But you're ignoring the analysis given in the article-- drivers already don't acknowledge speed limits. From the article: > Luckily, there is some logic to the speed people choose other than the need for speed. The speed drivers choose is not based on laws or street signs, but the weather, number of intersections, presence of pedestrians and curves, and all the other information that factors into the principle, as Lt. Megge puts it, that “no one I know who gets into their car wants to crash.” Rather than speed limits, we need to look at other avenues to reduce pedestrian traffic deaths. Just shooting from the hip, I think that we could do more to communicate to drivers the presence of pedestrians, and to make sure that rural highways and boulevards have shoulders or sidewalks for pedestrians. A more complete analysis of pedestrian deaths: http://www.popcenter.org/problems/pedestrian_injuries/ http://www.popcenter.org/problems/pedestrian_injuries/ Here are some useful factoids: - Finally, the more one drinks, the higher the risk of being involved in a pedestrian-vehicle crash resulting in a fatality. One study found that out of 176 pedestrian fatalities, 86 of those involved pedestrians who had been drinking, nearly all of whom had BACs of 0.10 percent or more. - In addition, the same study noted that 71 percent of all fatal pedestrian-vehicle crashes in the United States in 2000 occurred in urban areas. - Finally, the majority of pedestrian injuries and fatalities happen to males between the ages of 25 and 44. This gives us a pretty targeted demographic! Start a "dangers of the road" campaign targeted at pedestrians who are men, aged 25-44, drink at night and who live in rural areas.
  • rayiner 9y ago
    The most effective thing, as shown in European cities, is to make it hard to speed. Have narrower roads that cannot be easily traversed at high speed. To see an example in the US, look at Center City Philadelphia. Outside a few major thoroughfares like Market Street, the roads are one way in each direction and very narrow. Walking as a pedestrian on Walnut (a major retail road) feels very safe.
    • tptacek 9y ago
      This is also an idea in Christopher Alexander's "Timeless Way Of Building" book, and a topic that's been taken up a bunch of times by the Strong Towns blog.
• Sir_Cmpwn 9y ago
  The solution is narrower lanes on side streets. Narrower lanes naturally makes people drive more slowly. Lowering the speed limit won't solve it. Bonus: making lanes narrower also makes room for bike lanes.
• rlpb 9y ago
  The author of the article already pointed out and rebutted your precise argument. Can you counter his rebuttal? If you can't, you've added exactly nothing to the debate.
• kstenerud 9y ago
  The article talked specifically about that exact scenario, and then concluded that a number on a sign won't make any difference in driver speed. Only proper road engineering can slow drivers down.
• koolba 9y ago
  Why should we care about pedestrians crossing highways? The biggest gains for something like this isn't a local side street. It's changing the interstate speed limit.
• thomastjeffery 9y ago
  > Results show that the average risk of severe injury I'll stop you right there. We are talking about how to prevent accidents, not how to make them less serious. I have often heard cited, the fact that force scales with acceleration in a non-linear way, as the reason for speed limits. That is not the case, nor should it be.
• jfoutz 9y ago
  I've read arguments that 20mph is the max theoretical running speed for a human. The argument goes evolution has finely tuned us to deal with anything below that speed, but above it, not so much.
• marcus_holmes 9y ago
  I lived on the Isle of Man, where there are very strict 30mph speed limits in the towns, but no speed limits outside the towns. The roads there are twisty, with dry stone walls either side, mostly. Except for the mountain roads that are spectacular. Then there's the TT, when bikers from all over the world come there to race, and about a dozen or so die each year. Apart from that, though, road fatalities are not exceptional. Driving there is great, because you don't have the constant worry of "am I going over the limit?" or "what is the limit here?". You stop worrying about the number, or checking your speedo, and concentrate on driving safely on the road. How fast or slow you're going becomes irrelevant, it's all about how you drive on the road you're given. The speed limit is as much a target as a limit. If the limit is 60 then there's a feeling that "well, they know their business, it must be safe to drive at 60 here". What is authorised becomes advised. No-one can blame you if you lose control due to speed, because you were driving under the speed limit so it must have been OK. With no limits, it becomes your responsibility to decide what's safe. And yes, there are people who think they can drive safely much faster than they actually can. But they they tend to head for the mountain roads where's less traffic to get in their way. There's also less macho bullshit around it because there's no "rebel cred" in driving over the limit when there is no limit. Conversely, driving slowly in town is accepted, because it's clearly done for good reasons. Speeding in town isn't socially acceptable (if you want to go fast, head to the mountain and do your worst). People drive more safely, and more courteously because they have responsibility. It's a great system. I wish we adopted it here in Australia.
  • wobbleblob 9y ago
    A friend of mine lives, well lived, on the Isle of Man. He's been in a rehabilitation center on the mainland for the past year, after being hit by a Ferrari driving at entitled velocity. Why do you even need cars there? Everything is within cycling distance.
    • marcus_holmes 9y ago
      horizontal rain... umbrellas don't survive there. I would hate to cycle there
  • 9y ago
• amorphid 9y ago
  I've been driving through rural Serbia for the past day on two lane highways with no sidewalks & not much of a shoulder. There are ton's of people walking along the edges of these streets, traveling from one town to the next. I even offered of a couple of them a ride, and they were happy to keep walking. Another man reading a newspaper was leaning up against a guardrail on the side of the road, again no sidewalk, on a two lane road with a speed limit of 80 kph. And I came across many tractors driving slowly, and a big cart of wood being being driven buy 2 peopled & pulled by oxen. I also drove by 2 kids walking side by side holding hands, walking along the edge of the road in the same lane I'm driving. These roads are not just for fast driving cars.
• sparky_ 9y ago
  I recently returned from vacation in Chile, where I noticed the majority of freeways had separate speed limits based on vehicle class. Two axle private vehicles had a speed limit of 130 km/h while trucks were only 100, and double-trailer trucks were slower still.
• reitanqild 9y ago
  Practical examples: 1. How not to do it IMO: Road next to me had a limit of 60 because of "road works", there even was a road works sign standing there. Everyone knew it was safe to drive 80. One day I was driving suddenly after months of inactivity a worker comes walking out into the road while I come driving. The sun was low and I just saw his legs moving and managed to brake and steer away. If I had crashed it would have been my fault - and I would have deserved jail and losing my license. But I totally wouldn't say road authorities would have been without blame: Designing a 80 zone, then training everyone to think the road works sign is just a forgotten artifact is really really not a good idea if you intend to suddenly send your people out there in low light. 2. How it should be done IMO: Next to a school that I sometimes drive past there is a 60 zone. But it (used to) only apply when kids could be reasonably expected to be there (0600 - 2000 or something). Every summer road authorities would even cross it out. This way we are constantly reminded about why there is a very valid reason to slow down at this place - and we are reminded that at least some of them honestly think before they restrict us.
• Markoff 9y ago
  i think the article is about highways and fast Intercity roads where pedestrians have no business to be and not local city communications. of course within city limits the speed should be as low as possible (most of EU is 50kmph, personally i would not mind even 35-40kmph) to discourage individual transport to motivate people to use public transport and this should come together with ban of cars older than 10-15 years not meeting current safety standards and of course all cars should be checked for quality of their brakes and other parts before being allowed to drive
• cowl 9y ago
  Your analysis is fine but there are plenty of cases when Pedestrians should not be factored and still the speed limit is too low. We are talking about one way highway traffic where no pedestrian can enter (or at least should not enter), where opposing traffic risk is Zero (one way), visibility very good etc. there are plenty of examples like this one where you really have to try hard to stay in the speed limit. and cases like this just make it hard to respect the speed limits even when they should be respected because they teaching us that the speed limits are arbitrary and we human beings do not like arbitrary things.
• u801e 9y ago
  One factor that you may not be considering is that by routinely posting overly low speed limits, the belief that the posted speed limit is the "moral minimum" speed or that it's okay to exceed it by a certain amount is reinforced. The speed limit is supposed to be the upper bound. By over using low speed limits, we indirectly increase the danger level for vulnerable road users because of the reasons detailed above.
• BearGoesChirp 9y ago
  Attempting to reduce pedestrian deaths using speed limits seems the wrong way to handle it. Attempting to limit 'bad' behavior doesn't work well. Just look at the war on drugs. It seems like it would compared to a wild west situation where everyone is doing lots of drugs/going as fast as possible, but in our current society cracking down further offers no further benefits and may come at additional costs. For example: Automatic breaking technology on cars that can detect people who the driver might not be able to see (child running out from in-between parked cars). Better selective enforcement of speed limits so that people pay a bit more attention. When an empty country road says 25mph due to a speed trap, it reduces the trust people place in speed limits, meaning they won't respect the 25mph speed limit as much even when it is in a school zone where children are constantly crossing the street. Better side walk design. I shouldn't be only two feet from a speeding 2 ton object even when everyone is following the law correctly. Having space between the road and sidewalk helps. Maybe add some trees and other objects that will stop a drunk driver who runs off the road. Bike paths for those riding bikes. Also separated from the road.
  • mikepurvis 9y ago
    Having a super-wide "complete street" with separated bike lanes and set back sidewalks everywhere isn't realistic, particularly in mature neighbourhoods. I mean, we already have fully separated car-only thoroughfarse— they're the interchange-access highways. I'd rather figure out how to make city drivers more attentive and responsible than effectively turn every arterial road into a mini highway.
• mdip 9y ago
  A good chunk of this article talked about Michigan and the reasoning behind its increasing speed limits, but it somewhat failed to address your point, so I'll do so since I know a bit about this subject (hell, everyone who lives in Michigan at a certain age becomes an expert on these things -- there's nothing resembling useful public transportation here). We have several cities, but they're somewhat small by comparison to some of the places a lot of HN readers are from. There's no analog to SF/Silicon Valley here. Sure, people walk around Detroit, but for the most part, that's down-town in a few select areas (yes, people do walk in the outskirts, as well, but there are much larger dangers going on there than pedestrian fatalities). There are several other cities where there is a lot of walking traffic. The speed limits are 25MPH in all of the places you'd expect them to be[0]. The 85th percentile rule does not apply in these cases nor does it apply on residential roads. I live on a main subdivision road and folks commonly exceed 25MPH. I call the cops when I see it and they've had patrols going on in my neighborhood every day for the last two weeks (it's very profitable for them). People are finally slowing down again. You will get pulled over for going 5MPH over the limit in these situations, whereas that would never happen on a main road unless you were doing something else wrong. I'm a huge supporter of the 85th percentile rule, but only when applied outside of these cases. Yes, people walk on the county/state roads that are set by this rule, but there are proper signals with increased delay times when pedestrians push the magic button (which, on these roads, actually does something -- the walk/don't walk signals won't turn to walk ... ever ... if the button isn't pressed). On freeways, there's no pedestrian traffic (on purpose, anyway). [0] My daughter is hard of hearing (with hearing aids and all) and ADHD. She's the kid who's going to chase a ball into the road without looking and not have strong enough hearing to notice a car before it's too late (she rarely wears the hearing aids at play outside to fear of damaging them). I have followed kids home in my car and had discussions with their parents about their driving. I stick with the rule of "keep up with traffic" and will speed when that's how fast everyone else is going, but I never exceed the speed limit in pedestrian areas and I hope most adults follow suit ... though if my neighborhood is any indication, the worst time for speeding is when parents are heading to the Elementary school (located in my neighborhood!) to pick up their children. They'll blow past the crossing guards while kids are walking home from school doing 40 MPH. I guess if it's not their kid on side-walk, some folks feel it's more important to get where their going.
• kazinator 9y ago
  There is a 10% chance of not being severely injured when struck at 46 mph? Amazing.