Traffic safety advocates want speed humps on more streets. They demonstrably slow down drivers and therefore reduce traffic collisions. That saves lives—and keeps everyone's insurance premiums...
Traffic safety advocates want speed humps on more streets. They demonstrably slow down drivers and therefore reduce traffic collisions. That saves lives—and keeps everyone's insurance premiums lower.
However, even when provably beneficial safety infrastructure like speed humps would stop drivers from speeding on roads, some local residents (uninformed and with incorrect perceptions of what such a measure does) are wont to complain to transit authorities about legitimate safety proposals. Such NIMBY fears are unwarranted, misleading, and statistically dangerous. Pointless resistance to safety infrastructure that reduces both pedestrian and driver fatalities should not be accepted as valid by transit agencies. However, these agencies often end up capitulating to such frivolous demands anyway.
After six months, DDOT tentatively agreed to install two speed humps on this block—but not without asking for community feedback first. DDOT heard from two residents who opposed the project, complaining about a speed hump’s effects on parking and road repairs, neither of which would be affected.
DDOT quietly halted the speed hump installation in the face of their “uncertainty” about community support. Instead, DDOT commissioned a speed study that found that over 40 percent of the cars on that block exceeded the speed limit, and that over the course of two days, 22 cars had reached speeds more than 10 mph over the speed limit (including one car traveling between 40-45 mph on a 20 mph neighborhood street).
But by DDOT’s standards, this level of speeding was insufficient to require traffic calming, particularly in the face of uncertain community support.
Two residents with hazy opposition to traffic calming should not be able to derail safety measures with well-timed emails. It shouldn’t take concerted community mobilization and passage of an ANC resolution just to try to get speed humps on one block.
Not only is this approach bad for safety, but it also raises fairness concerns – many people and communities simply aren’t going (or able) to go through this much work for each incremental improvement. DDOT has previously acknowledged that highly reactive traffic safety systems can compound inequity by favoring those with the time, attention, and engagement with city services necessary to push for improvements.
Traffic safety measures should not be this difficult to install. There ought to be raised crosswalks on significantly more local streets than we currently see: these act as speed humps or speed tables. Even in absence of actual pedestrian crossings, it's important to keep drivers going the actual speed limit or lower by installing speed humps in places where drivers are likely to exceed safe speeds. The worst offenders—those most likely to cause a collision—will not drive slowly voluntarily. We must design streets to have slow traffic, not ask drivers to slow down: "Pretty please? Pleeeease?" is not effective. "Slow down or your suspension gets annihilated!" is effective. That's why speed humps work.
We must also demystify traffic calming measures: communities should want universally slow traffic, and that requires infrastructure that forces it. It should be common for people to ask for infrastructure that empirically reduces automobile speeds. It should not be common for them to nearly unilaterally block safe, meaningful proposals on unreasonable grounds. This all starts with education: cars are dangerous. The higher the speed, the more they kill. Slow them down significantly, and they're safer. We want our communities to be safe: so slow down the cars!
I agree with all your points there but just want to give a cyclist's perspective on yiur choice of speed bump. In London, where I live the two most common speed bumps are the: three foot wide 6-8...
I agree with all your points there but just want to give a cyclist's perspective on yiur choice of speed bump.
In London, where I live the two most common speed bumps are the: three foot wide 6-8 inch tall tarmac speed bumps that go all the way across the street; and the three mounds speed bumps that are a similar height and width -> | 0 0 0 | kind of thing. These are usually deployed on residential streets with cars parked on both sides so only the middle bump is visible.
The first type are great. As long as you lift your bum off your saddle slightly you can glide over them on a bike without slowing down. They only become an issue when you have one of those drivers that absolutely must pass lowly cyclists so are hitting the speed bumps like the Dukes of Hazard. The second type, however, channel traffic into the centre of the road (if they want to avoid the bumps). This causes drivers to swerve in on you closing the passing gap if they are passing you on your bike as they go over the bump or terrifyingly swerve towards you if they are coming the other direction. It's frustratingly dangerous as a cyclist. Feckless or inattentive drivers that had been terrorising us with their speeding are now swerving into us instead.
So the reason for the three bumps is for allowing emergency vehicles to pass at full speed. Well designed bumps are wide enough to let emergency vehicles do this, but not regular traffic. I'm pro...
So the reason for the three bumps is for allowing emergency vehicles to pass at full speed. Well designed bumps are wide enough to let emergency vehicles do this, but not regular traffic.
I'm pro speed bump but also understand why jostling people on stretchers is also bad.
Doesn't stop dum dums from trying and only getting half their car on the bump, doing more damage to both themselves and risking everyone else.
That's my understanding of them too but very few of them are properly spaced. Most vehicles can speed over them without hitting a bump if they swerve to the centre of the road. It's a lot harder...
That's my understanding of them too but very few of them are properly spaced. Most vehicles can speed over them without hitting a bump if they swerve to the centre of the road.
It's a lot harder to mess up the speed bump that goes all the way across.
The Federal Highway Administration states that raised crosswalks (functionally equivalent to full-width speed humps) "should generally be avoided on truck routes, emergency routes, and arterial...
The Federal Highway Administration states that raised crosswalks (functionally equivalent to full-width speed humps) "should generally be avoided on truck routes, emergency routes, and arterial streets." Note the use of "generally," but even so this is a car-centric guideline: arterial roads are some of the most dangerous we have for pedestrians. Arterials comprise 13% of roadways but are the location of 59% of fatal pedestrian deaths (pg. 6) caused by motor vehicles. Excepting highways, why do we prioritize freight (truck) throughput by literally a matter of seconds over reducing fatalities (a matter of eternity)? The authors of this guideline prefer to maximize traffic throughput rather than minimize the loss of human life. I'm sure they've done the actuarial math to conjure up some figures, but I don't find it appropriate.
By "emergency routes" this guideline apparently more specifically refers to "primary emergency vehicle routes"; though it does not specify whether this means evacuation routes or preset routes that an emergency vehicle might... choose to use? (How that is functionally different from an arterial, I could not say.) I have to admit I would find the former questionable. No population-wide evacuation using automobiles will ever avoid complete gridlock, including on highways (where you wouldn't install humps to begin with); max speed is almost irrelevant. If the latter: an understandable critique, but in theory, an emergency vehicle may have to take literally any street to reach an emergency, and if these humps on residential streets are fundamentally incompatible with emergency vehicle travel, they would surely have a problem with all humps. Yet evidently real-world operation demonstrates that this is not the case, considering that full-width speed humps are perfectly road-legal on such streets. I see why a full-width hump may encourage emergency vehicle drivers to slow down slightly but I am not sure this is really a necessity? (Very tall speed bumps are likely a different matter; as I understand it they are not something you see on public roadways.)
Delaying emergency vehicles from reaching an emergency is considered unwise. Reasonable. I agree. But if that comes at the expense of the health and safety of other pedestrians (if there is no hump, and a speeding emergency vehicle hits them) and potentially cyclists (if the hump encourages a sudden, dangerous swerve)... I think we're missing the point. While I see some data on pedestrian deaths from emergency vehicles, I do not know if there is specifically data available about the number of pedestrian/other fatalities caused by emergency vehicles charted against VMT; if compared to the portion of VMT driven by emergency vehicles, perhaps this data would be clarifying. I have scanned quickly online, but I seem to lack the ideal search query. In absolute terms the numbers do not appear enormous, but per capita/VMT it may be a different matter. Speeding is an issue for all drivers, not just civilians.
In practice I don't know how true it is to suppose that full-width speed humps pose a serious problem to emergency vehicles in general. I know it's right there in the FHWA guidelines, but I have asked this specific question to firefighters in the past and their response was something to the effect of, "It makes minimal difference. The truck can get over a speed hump just fine." (At neighborhood meetings proposing the installation of speed humps, as a matter of fact...) Those are actual firefighters who are actually driving the vehicles, not planners theorizing over models. Anecdotal for sure, but it would lead me to a tentative conclusion that it's more convenient and/or comfortable for emergency vehicle operators to drive at [near?-]full speed over speed humps, but not a mechanical requirement for their vehicles. (I have not asked ambulance drivers their opinion as I don't know any, I think.) I realize why time-to-respond is the pressing concern here, not fire truck suspension maintenance bills, but from those conversations it seemed to me to simply not be a problem worth complaining about for any reason. Just thinking it through, I would find it hard to believe there that a 0.5 second deceleration slowdown from a speed hump comprises a meaningful proportion of the time-to-respond, which is probably more dependent on whether a city has bothered to create a dedicated bus rapid transit lane that might be used by an emergency vehicle. (In general, the dearth of such lanes is telling. But in both their presence and absence, the sprawling design of our cities and the habit of confused civilian drivers to inadvertently block emergency vehicles seems like more of a concern.)
If it's possible to make humps easily passable by emergency vehicles and not by regular vehicles, that's great, though with how wide modern pickup trucks are, I am uncertain how feasible that is. (You could make it wide enough to slow a pickup but not a fire truck, but if I'm not mistaken I believe that an ambulance is closer to the former in width than the latter, so it would seem perhaps a half-measure.) And if foolish drivers are going to attempt to avoid a half-width speed bump (futile or not) and maybe put cyclists at risk, it's unclear to me if it is worthwhile to use these segmented/non-full-width speed humps at all.
I recognize that there are situations where full-width speed humps are potentially harder to justify, though I am hesitant to obey prevailing federal theory without some prodding. Their guidelines are not rooted in a Vision Zero approach, they are rooted in a "move as many cars as possible from point A to point B" approach. Also, despite my essay-length comment here, this sub-topic actually isn't something I have a super strong opinion on, nor is it something about which I know a particular amount. Ultimately, the guidelines are what they are, and they're there for a reason. I still think we cut cars—whatever form they take—a bit too much slack.
Having called 911 for ambulances before, seconds count when someone is not breathing or is bleeding out. Ditto for fire services and smoke inhalation. There are few circumstances where I support...
Having called 911 for ambulances before, seconds count when someone is not breathing or is bleeding out.
Ditto for fire services and smoke inhalation.
There are few circumstances where I support vehicles going over 35 outside of dedicated highways, but emergency services booking as fast as possible is one of those.
Plus on the way back, with a potentially unstable patient who could have further injuries while jostling (say spine fracture), I am hesitant to fully endorse full speedbumps everywhere.
I'd support putting governers on cars limiting them to 30 mph unless on a freeway first.
Minimizing turbulence for injured passengers would seem to be a more compelling reason than a potential second-long slowdown (which, for comparative reasons described above, is probably not the...
Minimizing turbulence for injured passengers would seem to be a more compelling reason than a potential second-long slowdown (which, for comparative reasons described above, is probably not the first traffic device I would focus on), though I agree and totally acknowledge what you're saying!
Oh yea, I agree. Like, despite seconds counting, emergency vehicles also shouldn't speed or run stoplights at full speed for those reasons. Shaving off 3 seconds is less important than not making...
Oh yea, I agree. Like, despite seconds counting, emergency vehicles also shouldn't speed or run stoplights at full speed for those reasons.
Shaving off 3 seconds is less important than not making 4 more bodies. Lotta dimensions there, and sadly most mitigating things will have selfish butts looking to exploit them.
I agree that a speed hump should be full-width in order to stop drivers from swerving and putting cyclists at risk. I also agree that it should be gradual enough for bikers to reasonably get over...
I agree that a speed hump should be full-width in order to stop drivers from swerving and putting cyclists at risk. I also agree that it should be gradual enough for bikers to reasonably get over (though I think a minor slowdown at a pedestrian crossing is reasonable, even for cyclists). This is why I typically prefer proper asphalt speed humps to half-width plastic speed humps: the former are actually part of the road and the latter are just additions. The triple-bulb design you describe sounds like it would be plenty cost-effective, which is probably why your council did it, but not necessarily the best long-term infrastructure decision. Not safe at all. It's definitely important to design traffic calming measures with cyclists in mind!
Cyclists are enemy #2 to pedestrians, at least around me. It doesn't help that too many of all categories don't know the rules (pedestrians walk against traffic flow, cyclists with cars, cars...
Cyclists are enemy #2 to pedestrians, at least around me. It doesn't help that too many of all categories don't know the rules (pedestrians walk against traffic flow, cyclists with cars, cars yield to everyone, etc) At least pedestrians and cyclists are less likely to kill each other.
Pardon my french, but arseholes are enemy no's 1-100. Arseholes in cars, arseholes on bikes, arseholes on foot etc... The vast majority of people are decent. It's encounters with a few arseholes...
Pardon my french, but arseholes are enemy no's 1-100. Arseholes in cars, arseholes on bikes, arseholes on foot etc... The vast majority of people are decent. It's encounters with a few arseholes that ruin your day. And well, humans being humans, we tend to try to differentiate ourselves from the arseholes. So instead we see the driver/cyclist/pedestrian that we are not. And conversely make special pleadings for those like us.
Obviously there's a whole range of ifs and butts. My general point is pushing against pointless atomisation of society. When the significant difference is people that don't have a close reign on their inner arsehole and the rest of humanity.
You've inspired me to research data on pedestrian fatalities in motor vehicle collisions broken down by vehicle type. Unfortunately, I've been unable to find comprehensive data that isn't 20 years...
You've inspired me to research data on pedestrian fatalities in motor vehicle collisions broken down by vehicle type. Unfortunately, I've been unable to find comprehensive data that isn't 20 years old.
The paper that seems to be getting citations on random transit articles is "United States pedestrian fatality rates by vehicle type" (Paulozzi 2005). It states that "[p]assenger cars and light trucks (vans, pickups, and sport utility vehicles) accounted for 46.1% and 39.1%, respectively, of the 4875 deaths [in 2002], with the remainder split among motorcycles, buses, and heavy trucks." It goes on to describe the "relative risks" of each mode, which I assume is some kind of normalized form of the absolute data, but I am too stupid to completely understand the formal statistical definition of that term. (I am not sure if this is specifically meant to provide a per-capita-adjacent perspective or if it's just some statistician geek stuff. If anyone knows, please feel free to clarify.)
Compared with cars, the RR of killing a pedestrian per vehicle mile was 7.97 (95% CI 6.33 to 10.04) for buses; 1.93 (95% CI 1.30 to 2.86) for motorcycles; 1.45 (95% CI 1.37 to 1.55) for light trucks, and 0.96 (95% CI 0.79 to 1.18) for heavy trucks. [...] The risk of killing a pedestrian per vehicle mile traveled in an urban area was 1.57 times (95% CI 1.47 to 1.67) the risk in a rural area.
It would seem that the main antagonists are cars, followed by buses, motorcycles, and trucks, unless I am grossly misinterpreting this paragraph. (Again, please correct me if I am.)
This study does not evaluate bicycles as a mode because the concept of cycling was apparently unknown in 2005 (at least to the National Highway Traffic Safety Administration's Fatality Analysis Reporting System). While I can find any number of studies about how cars kill cyclists, I actually can't find anything recent about how cyclists cause pedestrian fatalities. I am certain that there must be some such instances. The NHTSA FARS doesn't really seem to document this, unless I'm missing or misreading something.
The closest I can get is small studies about shared-use paths for pedestrians and cyclists. "Pedestrian-Cyclist Collisions: Issues and Risk" (Grzebieta et al. 2011) is vaguely critical of this design choice and seems to conclude that it is not meaningfully more dangerous for pedestrians to share pathways with cyclists than for each mode (pedestrian, bicycle, car) to have completely separate infrastructure:
Whilst there are a large number of traffic related cycling deaths and pedestrian deaths (numbering in the many hundreds over the five year period), only four fatalities were identified in NCIS that have resulted specifically from a cyclist – pedestrian collision for the period 2001 to 2006. In all four fatalities the pedestrian died as a result of the impact. No cyclist fatality has been recorded resulting from a cyclist crashing into a pedestrian. However, when a pedestrian is killed in such an event it is usually elevated in the media profile. [...] Three of the cases directly related to a bicyclist not being capable of stopping in time and striking the pedestrian down. [The fourth was a criminal matter.]
If we have had only one fatality in NSW over a five year period being in Sydney’s CBD, this means that the risk of a pedestrian being struck by a cyclist is of the order 1 in every 75 million trips, i.e. an extremely rare event. [...] This comparison indicates that the risk of a pedestrian being struck down by a bicyclist and killed is currently less than the risk of being struck by lightning (0.1 chances of fatality per million person years), 23 times less likely than tripping on a footpath or roadway (1.15 chances of fatality per million person years), 200 times less likely being involved in an airline crash (10 chances of fatality per million person years), and 700 times less likely than being struck and killed by a motor vehicle (35 chances of fatality per million person years).
So even "in regards to risk per number of trips," apparently the mortal hazard that bicycles offer to pedestrians on shared-use paths is relatively insubstantial. The article does talk a bit about injuries, which are also worth discussion:
Using the exposure data set out for the fatalities, this is 163 injuries per 75 million trips, or approximately 1 injury in every 460,000 trips. In person years, this represents 8.2 pedestrians injured per million person years. This appears to be an event which is around 8 times greater than tripping on a footpath and killing yourself as a result and just slightly less riskier than being killed in an airline crash event. In other words, it is still a very low risk event.
Again, this is an Australian dataset from 2001–2006. It also doesn't go into depth about speed limits on shared-use pathways, which I suspect is one of the critical factors here. I would be interested in reading more modern data applied to cities beyond just Sydney, Australia. The way that people ride their bikes is a little different now than it was 10+ years ago and also varies regionally. There are more casual riders now; that means more inexperienced riders. Our use of technology has also changed somewhat, so distracted cyclists may be more of an issue now than they were a decade ago.
If you have more resources about this specific issue, I would be very interested in reading them. It seems like the issue is almost completely un-studied.
Sorry, I was glibbly comparing cyclists vs "All motor vehicles." Sorry to put you through that work. OTOH, I'm very intrigued by what you dug up, so it won't be in vein.
Sorry, I was glibbly comparing cyclists vs "All motor vehicles."
Sorry to put you through that work. OTOH, I'm very intrigued by what you dug up, so it won't be in vein.
The surprising prevalence of what seem to be "anti-everything" residents in the US has been a growing frustration for me. Any change, even if it demonstrably benefits everybody, takes an...
The surprising prevalence of what seem to be "anti-everything" residents in the US has been a growing frustration for me. Any change, even if it demonstrably benefits everybody, takes an inordinate amount of effort to enact thanks to those who got some kind of weird propaganda-twisted idea of what the changes are actually about, are simply selfish and want nothing that could potentially benefit groups they don't belong to, or are just chronic contrarians.
I have no idea how towns and cities in the US are supposed to ever improve or even avoid decay with the amount of power this group wields.
My city refuses to put speed humps on our street even after multiple petitions because they say it’s an emergency vehicle route for the nearby fire station. It doesn’t make much sense though -...
My city refuses to put speed humps on our street even after multiple petitions because they say it’s an emergency vehicle route for the nearby fire station. It doesn’t make much sense though - there’s an arterial road one block over running parallel to my street moving traffic much more effectively.
If anything, my street makes a poor emergency vehicle route because there are stop signs every 2-3 blocks, parallel parked cars narrowing traffic flow, and a 2 square blocks park that‘s the source of a lot of foot traffic. People still speed and blow through stop signs regularly.
None of these are a factor on the arterial road, and that road has both bike lanes and a dedicated turn lane (in addition to 1 lane of traffic each direction), so an emergency vehicle has plenty of space to maneuver even if traffic is backed up.
A neighborhood adjacent to mine had them installed at one point, but the homeowners nearby petitioned to have them removed. They were sick of hearing vehicles accelerate after hitting the humps,...
A neighborhood adjacent to mine had them installed at one point, but the homeowners nearby petitioned to have them removed. They were sick of hearing vehicles accelerate after hitting the humps, which I think is a valid concern for those who live nearby. I also don't think they're all that effective, given a range of vehicle sizes. Trucks can go over most humps with no issue, unless they're so large that lower vehicles bottom out and scrape the road when they go over.
At the end of the day, there are better traffic calming methods.
I've noticed this is frequently an issue with speed bumps in parking lots: they're often very high in order to have an effect on large SUVs and trucks, but you have to be very careful to avoid...
I've noticed this is frequently an issue with speed bumps in parking lots: they're often very high in order to have an effect on large SUVs and trucks, but you have to be very careful to avoid scraping a hatchback or sedan. And some cars are even lower. Municipal ones are often lower, but some jacked up truck or Jeep will go through at full speed like it's nothing.
Narrowing roads that are meant to be taken slow and installing chicanes are more effective approaches. Roundabouts also slow down traffic, while (oddly enough) reducing overall trip times as opposed to four way intersections.
Roundabouts are an interesting study on the psychology of transportation because they demonstrate the distinction between perceived improvements to throughput and actual improvements. From the...
Roundabouts are an interesting study on the psychology of transportation because they demonstrate the distinction between perceived improvements to throughput and actual improvements. From the driver's perspective, roundabouts are a slowdown because, well, they force you to slow down. But when a traffic engineer analyzes average speed through a roundabout intersection vs. a signalized intersection, the roundabout can lead to a smoothing of overall traffic flow and faster trip times end-to-end. This is because signalized intersections incur heavy dwell times as traffic going in one direction pauses to allow the other direction to flow. In a roundabout, traffic slows, but never stops. How cool!
Empirical data supports the hypothesis that speed humps meaningfully reduce driver speed. The specific amount varies, but it could easily be a 40% reduction in speed from the baseline. In general,...
I also don't think they're all that effective, given a range of vehicle sizes.
Empirical data supports the hypothesis that speed humps meaningfully reduce driver speed. The specific amount varies, but it could easily be a 40% reduction in speed from the baseline. In general, it is important and necessary to use a combination of traffic calming methods in our streets. We could use more speed humps: but they also aren't the end-all-be-all. As stated, there are many ways to complement speed humps. These include:
Eliminating automobile traffic lanes
Narrowing automobile lanes
Creating a sense of enclosure by planting trees along sidewalks
Turning signalized intersections into roundabouts
Adding curb bump-outs, especially at intersections
Displaying the driver's current speed with active speed monitoring devices
Inserting rumble strips into the road surface
Painting eye-catching illusions to subconsciously draw attention to speed
...and much more!
A great city makes use of pretty much all of these. The goal ultimately has to get vehicles down to safe speeds, and the way that looks is going to vary quite a bit depending on the street in question.
I'm sure they're effective, but they come at a cost - vehicle wear and tear, ineffectiveness for larger vehicles, increased noise and reduced fuel consumption due to acceleration after clearing...
I'm sure they're effective, but they come at a cost - vehicle wear and tear, ineffectiveness for larger vehicles, increased noise and reduced fuel consumption due to acceleration after clearing the hump.
I am not aware of much formalized data on the particular issues you bring up, but other than slightly increased area noise (which I understand and appreciate) I don't think they are meaningfully...
I am not aware of much formalized data on the particular issues you bring up, but other than slightly increased area noise (which I understand and appreciate) I don't think they are meaningfully significant. At least, a 40% reduction in speed and resultant pedestrian injuries/deaths avoided is well worth negligible side effects.
It is probably not true to suggest that speed humps are ineffective at slowing down larger vehicles, though I understand why anecdotally that might feel reasonable. The data provided suggests otherwise. Other users in this thread actually had the exact opposite reason: feeling that speed humps are too effective at slowing down larger vehicles, specifically emergency vehicles! Surely both cannot be true. :) Indeed there can be some difference in behavior (pg. 8) depending on the design of speed hump, bump, slot, cushion, table, etc. in question. Some designs are specifically meant to permit passage of specific kinds of vehicles, to varying levels of success. And clearly some designs are superior to others: safer, less safe; more likely to be abused by drivers (see "lateral placement analysis," pg. 10); more expensive; and so on. The study classifies traffic into the following groups: "Passenger car; Luxury / High performance car; Pick-Up Truck; SUV / Minivan; Trucks; Buses; and Other (service vans, etc)." Table 5 demonstrates that "No one vehicle group performed differently than any other vehicle group for a given type of device" (pg. 10). That is: speed humps meaningfully slow everyone down. Just what the data says. :P
Unless a low or medium-clearance driver hits a speed hump at max speed (statistically not that common: humps are signed), a speed hump has a negligible (near-zero, or unobservable) effect on "wear and tear." Most speed humps are around 12 feet in depth with a height of only 3–4 inches. They are designed not to damage low vehicle undercarriages, and if taken at proper speeds, they don't. If a driver chooses to take a speed hump with typical signage at a speed they are not permitted to drive, any corresponding maintenance bill is their problem as an inattentive and dangerous individual driver, not a concern of the municipality. Speed humps and similar measures intentionally target drivers' aversion to damaging their personal vehicles, as well as their desire for a non-bumpy ride. It's the thought (real or perceived) of vehicle damage and general discomfort that slows them down; and that thought works, as evidenced by the data linked.
The amount of fuel inefficiency induced by a slowdown on the order of five seconds is a rounding error. Speed humps are also often placed near spots where drivers must slow down anyway, such as crosswalks.
No piece of infrastructure is technically free of externalities, but the issues described are not meaningful problems with speed humps! Even loud engine noise resulting from acceleration after a speed bump (which is an observable problem) may potentially be addressed with complementary traffic calming techniques, like gentle rumble strips and/or narrowing/eye-catching lane patterns that discourage high-speed driving, for example. It is probably not valuable to completely discard speed humps as a traffic calming device on the basis that they have some inherent flaw; this ignores the reality of emergent traffic behavior stemming from complex combinations of multiple devices. Like many other issues in urban planning, we can often solve these problems with greater creativity.
I have never seen a lifted ambulance. I'm sure they have better suspensions than most cars, but pickup trucks lifted so high that you need a ladder to get in them aren't going to need to speed...
users in this thread actually had the exact opposite reason: feeling that speed humps are too effective at slowing down larger vehicles, specifically emergency vehicles! Surely both cannot be true. :)
I have never seen a lifted ambulance. I'm sure they have better suspensions than most cars, but pickup trucks lifted so high that you need a ladder to get in them aren't going to need to speed bumps that bring an ambulance nearly to a stop.
I also see claims in this discussion like "if traffic slows down, that must decrease pedestrian fatalities. It's a reasonable hypothesis, but without the data, it's nothing more than a guess. For all we know, pedestrians could be more likely to be hit because drivers who are angry at the slowdown are now blindly flooring it to get back up to speed.
Additionally, this just feels like a bad case study. Only 40% of vehicles surpassed the speed limit of 20 mph?? That alone seems nearly impossible in this country. Only 22 cars during the entire traffic study reached 30 mph and only one reached 40 mph! It seems like either this is an area with people who already drive slowly or just almost no traffic. I don't even know the last time I saw a road with a 20 mph speed limit, much less a 20 mph speed limit than anyone obeyed. Frankly, I don't see how these numbers are even possible in a city like DC.
By "large vehicles", I specifically had pickup trucks and large SUVs in mind. Relatively light vehicles with high clearance and long suspension travel. Fire trucks and ambulances, while large, do...
By "large vehicles", I specifically had pickup trucks and large SUVs in mind. Relatively light vehicles with high clearance and long suspension travel. Fire trucks and ambulances, while large, do not meet the same criteria. The large mass of a fire engine will have a more difficult time going over a speed hump than a pickup truck just because of its weight.
Clearance is a problem for lower vehicles, as is often evidenced by gouges in the road around the speed bumps from cars bottoming out. I understand that theoretically, this should not be the case. But it is.
The amount of fuel inefficiency induced by a slowdown on the order of five seconds is a rounding error.
It's not. This is a study from the NIH that shows that ground pollution near speed bumps from brake, tire and exhaust emissions increased by 3x in the vicinity of speed bumps. And this is a study showing a 2-5x increase in emissions at the site of a speed bump, depending on the shape of the bump and emissions being measured.
I'm not saying that we shouldn't have any speed bumps, or that they're never worth the safety gains that can be made by installing them. But these are indeed disadvantages that shouldn't be discounted, hence the lengthy process in getting them installed (as opposed to someone just plopping them down everywhere).
Fascinating to see a figure put on the emissions/pollution differential occuring around speed bumps, thanks for posting that. It's a really thorny issue and, as ever, the law of unintended...
Fascinating to see a figure put on the emissions/pollution differential occuring around speed bumps, thanks for posting that. It's a really thorny issue and, as ever, the law of unintended consequences is just waiting to pounce on any knee-jerk reaction.
There was up to a 5x increase in emissions, but we're talking about an area that takes normal cars just a few seconds to pass through. So it really matters how many of these you're installing. If...
There was up to a 5x increase in emissions, but we're talking about an area that takes normal cars just a few seconds to pass through. So it really matters how many of these you're installing. If you install enough of them, it would really make a great case for electric cars.
Traffic safety advocates want speed humps on more streets. They demonstrably slow down drivers and therefore reduce traffic collisions. That saves lives—and keeps everyone's insurance premiums lower.
However, even when provably beneficial safety infrastructure like speed humps would stop drivers from speeding on roads, some local residents (uninformed and with incorrect perceptions of what such a measure does) are wont to complain to transit authorities about legitimate safety proposals. Such NIMBY fears are unwarranted, misleading, and statistically dangerous. Pointless resistance to safety infrastructure that reduces both pedestrian and driver fatalities should not be accepted as valid by transit agencies. However, these agencies often end up capitulating to such frivolous demands anyway.
Traffic safety measures should not be this difficult to install. There ought to be raised crosswalks on significantly more local streets than we currently see: these act as speed humps or speed tables. Even in absence of actual pedestrian crossings, it's important to keep drivers going the actual speed limit or lower by installing speed humps in places where drivers are likely to exceed safe speeds. The worst offenders—those most likely to cause a collision—will not drive slowly voluntarily. We must design streets to have slow traffic, not ask drivers to slow down: "Pretty please? Pleeeease?" is not effective. "Slow down or your suspension gets annihilated!" is effective. That's why speed humps work.
We must also demystify traffic calming measures: communities should want universally slow traffic, and that requires infrastructure that forces it. It should be common for people to ask for infrastructure that empirically reduces automobile speeds. It should not be common for them to nearly unilaterally block safe, meaningful proposals on unreasonable grounds. This all starts with education: cars are dangerous. The higher the speed, the more they kill. Slow them down significantly, and they're safer. We want our communities to be safe: so slow down the cars!
I agree with all your points there but just want to give a cyclist's perspective on yiur choice of speed bump.
In London, where I live the two most common speed bumps are the: three foot wide 6-8 inch tall tarmac speed bumps that go all the way across the street; and the three mounds speed bumps that are a similar height and width -> | 0 0 0 | kind of thing. These are usually deployed on residential streets with cars parked on both sides so only the middle bump is visible.
The first type are great. As long as you lift your bum off your saddle slightly you can glide over them on a bike without slowing down. They only become an issue when you have one of those drivers that absolutely must pass lowly cyclists so are hitting the speed bumps like the Dukes of Hazard. The second type, however, channel traffic into the centre of the road (if they want to avoid the bumps). This causes drivers to swerve in on you closing the passing gap if they are passing you on your bike as they go over the bump or terrifyingly swerve towards you if they are coming the other direction. It's frustratingly dangerous as a cyclist. Feckless or inattentive drivers that had been terrorising us with their speeding are now swerving into us instead.
So the reason for the three bumps is for allowing emergency vehicles to pass at full speed. Well designed bumps are wide enough to let emergency vehicles do this, but not regular traffic.
I'm pro speed bump but also understand why jostling people on stretchers is also bad.
Doesn't stop dum dums from trying and only getting half their car on the bump, doing more damage to both themselves and risking everyone else.
That's my understanding of them too but very few of them are properly spaced. Most vehicles can speed over them without hitting a bump if they swerve to the centre of the road.
It's a lot harder to mess up the speed bump that goes all the way across.
The Federal Highway Administration states that raised crosswalks (functionally equivalent to full-width speed humps) "should generally be avoided on truck routes, emergency routes, and arterial streets." Note the use of "generally," but even so this is a car-centric guideline: arterial roads are some of the most dangerous we have for pedestrians. Arterials comprise 13% of roadways but are the location of 59% of fatal pedestrian deaths (pg. 6) caused by motor vehicles. Excepting highways, why do we prioritize freight (truck) throughput by literally a matter of seconds over reducing fatalities (a matter of eternity)? The authors of this guideline prefer to maximize traffic throughput rather than minimize the loss of human life. I'm sure they've done the actuarial math to conjure up some figures, but I don't find it appropriate.
By "emergency routes" this guideline apparently more specifically refers to "primary emergency vehicle routes"; though it does not specify whether this means evacuation routes or preset routes that an emergency vehicle might... choose to use? (How that is functionally different from an arterial, I could not say.) I have to admit I would find the former questionable. No population-wide evacuation using automobiles will ever avoid complete gridlock, including on highways (where you wouldn't install humps to begin with); max speed is almost irrelevant. If the latter: an understandable critique, but in theory, an emergency vehicle may have to take literally any street to reach an emergency, and if these humps on residential streets are fundamentally incompatible with emergency vehicle travel, they would surely have a problem with all humps. Yet evidently real-world operation demonstrates that this is not the case, considering that full-width speed humps are perfectly road-legal on such streets. I see why a full-width hump may encourage emergency vehicle drivers to slow down slightly but I am not sure this is really a necessity? (Very tall speed bumps are likely a different matter; as I understand it they are not something you see on public roadways.)
Delaying emergency vehicles from reaching an emergency is considered unwise. Reasonable. I agree. But if that comes at the expense of the health and safety of other pedestrians (if there is no hump, and a speeding emergency vehicle hits them) and potentially cyclists (if the hump encourages a sudden, dangerous swerve)... I think we're missing the point. While I see some data on pedestrian deaths from emergency vehicles, I do not know if there is specifically data available about the number of pedestrian/other fatalities caused by emergency vehicles charted against VMT; if compared to the portion of VMT driven by emergency vehicles, perhaps this data would be clarifying. I have scanned quickly online, but I seem to lack the ideal search query. In absolute terms the numbers do not appear enormous, but per capita/VMT it may be a different matter. Speeding is an issue for all drivers, not just civilians.
In practice I don't know how true it is to suppose that full-width speed humps pose a serious problem to emergency vehicles in general. I know it's right there in the FHWA guidelines, but I have asked this specific question to firefighters in the past and their response was something to the effect of, "It makes minimal difference. The truck can get over a speed hump just fine." (At neighborhood meetings proposing the installation of speed humps, as a matter of fact...) Those are actual firefighters who are actually driving the vehicles, not planners theorizing over models. Anecdotal for sure, but it would lead me to a tentative conclusion that it's more convenient and/or comfortable for emergency vehicle operators to drive at [near?-]full speed over speed humps, but not a mechanical requirement for their vehicles. (I have not asked ambulance drivers their opinion as I don't know any, I think.) I realize why time-to-respond is the pressing concern here, not fire truck suspension maintenance bills, but from those conversations it seemed to me to simply not be a problem worth complaining about for any reason. Just thinking it through, I would find it hard to believe there that a 0.5 second deceleration slowdown from a speed hump comprises a meaningful proportion of the time-to-respond, which is probably more dependent on whether a city has bothered to create a dedicated bus rapid transit lane that might be used by an emergency vehicle. (In general, the dearth of such lanes is telling. But in both their presence and absence, the sprawling design of our cities and the habit of confused civilian drivers to inadvertently block emergency vehicles seems like more of a concern.)
If it's possible to make humps easily passable by emergency vehicles and not by regular vehicles, that's great, though with how wide modern pickup trucks are, I am uncertain how feasible that is. (You could make it wide enough to slow a pickup but not a fire truck, but if I'm not mistaken I believe that an ambulance is closer to the former in width than the latter, so it would seem perhaps a half-measure.) And if foolish drivers are going to attempt to avoid a half-width speed bump (futile or not) and maybe put cyclists at risk, it's unclear to me if it is worthwhile to use these segmented/non-full-width speed humps at all.
I recognize that there are situations where full-width speed humps are potentially harder to justify, though I am hesitant to obey prevailing federal theory without some prodding. Their guidelines are not rooted in a Vision Zero approach, they are rooted in a "move as many cars as possible from point A to point B" approach. Also, despite my essay-length comment here, this sub-topic actually isn't something I have a super strong opinion on, nor is it something about which I know a particular amount. Ultimately, the guidelines are what they are, and they're there for a reason. I still think we cut cars—whatever form they take—a bit too much slack.
Having called 911 for ambulances before, seconds count when someone is not breathing or is bleeding out.
Ditto for fire services and smoke inhalation.
There are few circumstances where I support vehicles going over 35 outside of dedicated highways, but emergency services booking as fast as possible is one of those.
Plus on the way back, with a potentially unstable patient who could have further injuries while jostling (say spine fracture), I am hesitant to fully endorse full speedbumps everywhere.
I'd support putting governers on cars limiting them to 30 mph unless on a freeway first.
Minimizing turbulence for injured passengers would seem to be a more compelling reason than a potential second-long slowdown (which, for comparative reasons described above, is probably not the first traffic device I would focus on), though I agree and totally acknowledge what you're saying!
Oh yea, I agree. Like, despite seconds counting, emergency vehicles also shouldn't speed or run stoplights at full speed for those reasons.
Shaving off 3 seconds is less important than not making 4 more bodies. Lotta dimensions there, and sadly most mitigating things will have selfish butts looking to exploit them.
I agree that a speed hump should be full-width in order to stop drivers from swerving and putting cyclists at risk. I also agree that it should be gradual enough for bikers to reasonably get over (though I think a minor slowdown at a pedestrian crossing is reasonable, even for cyclists). This is why I typically prefer proper asphalt speed humps to half-width plastic speed humps: the former are actually part of the road and the latter are just additions. The triple-bulb design you describe sounds like it would be plenty cost-effective, which is probably why your council did it, but not necessarily the best long-term infrastructure decision. Not safe at all. It's definitely important to design traffic calming measures with cyclists in mind!
Cyclists are enemy #2 to pedestrians, at least around me. It doesn't help that too many of all categories don't know the rules (pedestrians walk against traffic flow, cyclists with cars, cars yield to everyone, etc) At least pedestrians and cyclists are less likely to kill each other.
Pardon my french, but arseholes are enemy no's 1-100. Arseholes in cars, arseholes on bikes, arseholes on foot etc... The vast majority of people are decent. It's encounters with a few arseholes that ruin your day. And well, humans being humans, we tend to try to differentiate ourselves from the arseholes. So instead we see the driver/cyclist/pedestrian that we are not. And conversely make special pleadings for those like us.
Obviously there's a whole range of ifs and butts. My general point is pushing against pointless atomisation of society. When the significant difference is people that don't have a close reign on their inner arsehole and the rest of humanity.
You've inspired me to research data on pedestrian fatalities in motor vehicle collisions broken down by vehicle type. Unfortunately, I've been unable to find comprehensive data that isn't 20 years old.
The paper that seems to be getting citations on random transit articles is "United States pedestrian fatality rates by vehicle type" (Paulozzi 2005). It states that "[p]assenger cars and light trucks (vans, pickups, and sport utility vehicles) accounted for 46.1% and 39.1%, respectively, of the 4875 deaths [in 2002], with the remainder split among motorcycles, buses, and heavy trucks." It goes on to describe the "relative risks" of each mode, which I assume is some kind of normalized form of the absolute data, but I am too stupid to completely understand the formal statistical definition of that term. (I am not sure if this is specifically meant to provide a per-capita-adjacent perspective or if it's just some statistician geek stuff. If anyone knows, please feel free to clarify.)
It would seem that the main antagonists are cars, followed by buses, motorcycles, and trucks, unless I am grossly misinterpreting this paragraph. (Again, please correct me if I am.)
This study does not evaluate bicycles as a mode because the concept of cycling was apparently unknown in 2005 (at least to the National Highway Traffic Safety Administration's Fatality Analysis Reporting System). While I can find any number of studies about how cars kill cyclists, I actually can't find anything recent about how cyclists cause pedestrian fatalities. I am certain that there must be some such instances. The NHTSA FARS doesn't really seem to document this, unless I'm missing or misreading something.
The closest I can get is small studies about shared-use paths for pedestrians and cyclists. "Pedestrian-Cyclist Collisions: Issues and Risk" (Grzebieta et al. 2011) is vaguely critical of this design choice and seems to conclude that it is not meaningfully more dangerous for pedestrians to share pathways with cyclists than for each mode (pedestrian, bicycle, car) to have completely separate infrastructure:
So even "in regards to risk per number of trips," apparently the mortal hazard that bicycles offer to pedestrians on shared-use paths is relatively insubstantial. The article does talk a bit about injuries, which are also worth discussion:
Again, this is an Australian dataset from 2001–2006. It also doesn't go into depth about speed limits on shared-use pathways, which I suspect is one of the critical factors here. I would be interested in reading more modern data applied to cities beyond just Sydney, Australia. The way that people ride their bikes is a little different now than it was 10+ years ago and also varies regionally. There are more casual riders now; that means more inexperienced riders. Our use of technology has also changed somewhat, so distracted cyclists may be more of an issue now than they were a decade ago.
If you have more resources about this specific issue, I would be very interested in reading them. It seems like the issue is almost completely un-studied.
Sorry, I was glibbly comparing cyclists vs "All motor vehicles."
Sorry to put you through that work. OTOH, I'm very intrigued by what you dug up, so it won't be in vein.
The surprising prevalence of what seem to be "anti-everything" residents in the US has been a growing frustration for me. Any change, even if it demonstrably benefits everybody, takes an inordinate amount of effort to enact thanks to those who got some kind of weird propaganda-twisted idea of what the changes are actually about, are simply selfish and want nothing that could potentially benefit groups they don't belong to, or are just chronic contrarians.
I have no idea how towns and cities in the US are supposed to ever improve or even avoid decay with the amount of power this group wields.
My city refuses to put speed humps on our street even after multiple petitions because they say it’s an emergency vehicle route for the nearby fire station. It doesn’t make much sense though - there’s an arterial road one block over running parallel to my street moving traffic much more effectively.
If anything, my street makes a poor emergency vehicle route because there are stop signs every 2-3 blocks, parallel parked cars narrowing traffic flow, and a 2 square blocks park that‘s the source of a lot of foot traffic. People still speed and blow through stop signs regularly.
None of these are a factor on the arterial road, and that road has both bike lanes and a dedicated turn lane (in addition to 1 lane of traffic each direction), so an emergency vehicle has plenty of space to maneuver even if traffic is backed up.
A neighborhood adjacent to mine had them installed at one point, but the homeowners nearby petitioned to have them removed. They were sick of hearing vehicles accelerate after hitting the humps, which I think is a valid concern for those who live nearby. I also don't think they're all that effective, given a range of vehicle sizes. Trucks can go over most humps with no issue, unless they're so large that lower vehicles bottom out and scrape the road when they go over.
At the end of the day, there are better traffic calming methods.
I've noticed this is frequently an issue with speed bumps in parking lots: they're often very high in order to have an effect on large SUVs and trucks, but you have to be very careful to avoid scraping a hatchback or sedan. And some cars are even lower. Municipal ones are often lower, but some jacked up truck or Jeep will go through at full speed like it's nothing.
Narrowing roads that are meant to be taken slow and installing chicanes are more effective approaches. Roundabouts also slow down traffic, while (oddly enough) reducing overall trip times as opposed to four way intersections.
Roundabouts are an interesting study on the psychology of transportation because they demonstrate the distinction between perceived improvements to throughput and actual improvements. From the driver's perspective, roundabouts are a slowdown because, well, they force you to slow down. But when a traffic engineer analyzes average speed through a roundabout intersection vs. a signalized intersection, the roundabout can lead to a smoothing of overall traffic flow and faster trip times end-to-end. This is because signalized intersections incur heavy dwell times as traffic going in one direction pauses to allow the other direction to flow. In a roundabout, traffic slows, but never stops. How cool!
They're arguably better for emissions too, since they reduce travel times by cutting out wasted time sitting at idle.
Empirical data supports the hypothesis that speed humps meaningfully reduce driver speed. The specific amount varies, but it could easily be a 40% reduction in speed from the baseline. In general, it is important and necessary to use a combination of traffic calming methods in our streets. We could use more speed humps: but they also aren't the end-all-be-all. As stated, there are many ways to complement speed humps. These include:
A great city makes use of pretty much all of these. The goal ultimately has to get vehicles down to safe speeds, and the way that looks is going to vary quite a bit depending on the street in question.
I'm sure they're effective, but they come at a cost - vehicle wear and tear, ineffectiveness for larger vehicles, increased noise and reduced fuel consumption due to acceleration after clearing the hump.
I am not aware of much formalized data on the particular issues you bring up, but other than slightly increased area noise (which I understand and appreciate) I don't think they are meaningfully significant. At least, a 40% reduction in speed and resultant pedestrian injuries/deaths avoided is well worth negligible side effects.
It is probably not true to suggest that speed humps are ineffective at slowing down larger vehicles, though I understand why anecdotally that might feel reasonable. The data provided suggests otherwise. Other users in this thread actually had the exact opposite reason: feeling that speed humps are too effective at slowing down larger vehicles, specifically emergency vehicles! Surely both cannot be true. :) Indeed there can be some difference in behavior (pg. 8) depending on the design of speed hump, bump, slot, cushion, table, etc. in question. Some designs are specifically meant to permit passage of specific kinds of vehicles, to varying levels of success. And clearly some designs are superior to others: safer, less safe; more likely to be abused by drivers (see "lateral placement analysis," pg. 10); more expensive; and so on. The study classifies traffic into the following groups: "Passenger car; Luxury / High performance car; Pick-Up Truck; SUV / Minivan; Trucks; Buses; and Other (service vans, etc)." Table 5 demonstrates that "No one vehicle group performed differently than any other vehicle group for a given type of device" (pg. 10). That is: speed humps meaningfully slow everyone down. Just what the data says. :P
Unless a low or medium-clearance driver hits a speed hump at max speed (statistically not that common: humps are signed), a speed hump has a negligible (near-zero, or unobservable) effect on "wear and tear." Most speed humps are around 12 feet in depth with a height of only 3–4 inches. They are designed not to damage low vehicle undercarriages, and if taken at proper speeds, they don't. If a driver chooses to take a speed hump with typical signage at a speed they are not permitted to drive, any corresponding maintenance bill is their problem as an inattentive and dangerous individual driver, not a concern of the municipality. Speed humps and similar measures intentionally target drivers' aversion to damaging their personal vehicles, as well as their desire for a non-bumpy ride. It's the thought (real or perceived) of vehicle damage and general discomfort that slows them down; and that thought works, as evidenced by the data linked.
The amount of fuel inefficiency induced by a slowdown on the order of five seconds is a rounding error. Speed humps are also often placed near spots where drivers must slow down anyway, such as crosswalks.
No piece of infrastructure is technically free of externalities, but the issues described are not meaningful problems with speed humps! Even loud engine noise resulting from acceleration after a speed bump (which is an observable problem) may potentially be addressed with complementary traffic calming techniques, like gentle rumble strips and/or narrowing/eye-catching lane patterns that discourage high-speed driving, for example. It is probably not valuable to completely discard speed humps as a traffic calming device on the basis that they have some inherent flaw; this ignores the reality of emergent traffic behavior stemming from complex combinations of multiple devices. Like many other issues in urban planning, we can often solve these problems with greater creativity.
I have never seen a lifted ambulance. I'm sure they have better suspensions than most cars, but pickup trucks lifted so high that you need a ladder to get in them aren't going to need to speed bumps that bring an ambulance nearly to a stop.
I also see claims in this discussion like "if traffic slows down, that must decrease pedestrian fatalities. It's a reasonable hypothesis, but without the data, it's nothing more than a guess. For all we know, pedestrians could be more likely to be hit because drivers who are angry at the slowdown are now blindly flooring it to get back up to speed.
Additionally, this just feels like a bad case study. Only 40% of vehicles surpassed the speed limit of 20 mph?? That alone seems nearly impossible in this country. Only 22 cars during the entire traffic study reached 30 mph and only one reached 40 mph! It seems like either this is an area with people who already drive slowly or just almost no traffic. I don't even know the last time I saw a road with a 20 mph speed limit, much less a 20 mph speed limit than anyone obeyed. Frankly, I don't see how these numbers are even possible in a city like DC.
By "large vehicles", I specifically had pickup trucks and large SUVs in mind. Relatively light vehicles with high clearance and long suspension travel. Fire trucks and ambulances, while large, do not meet the same criteria. The large mass of a fire engine will have a more difficult time going over a speed hump than a pickup truck just because of its weight.
Clearance is a problem for lower vehicles, as is often evidenced by gouges in the road around the speed bumps from cars bottoming out. I understand that theoretically, this should not be the case. But it is.
It's not. This is a study from the NIH that shows that ground pollution near speed bumps from brake, tire and exhaust emissions increased by 3x in the vicinity of speed bumps. And this is a study showing a 2-5x increase in emissions at the site of a speed bump, depending on the shape of the bump and emissions being measured.
I'm not saying that we shouldn't have any speed bumps, or that they're never worth the safety gains that can be made by installing them. But these are indeed disadvantages that shouldn't be discounted, hence the lengthy process in getting them installed (as opposed to someone just plopping them down everywhere).
Fascinating to see a figure put on the emissions/pollution differential occuring around speed bumps, thanks for posting that. It's a really thorny issue and, as ever, the law of unintended consequences is just waiting to pounce on any knee-jerk reaction.
There was up to a 5x increase in emissions, but we're talking about an area that takes normal cars just a few seconds to pass through. So it really matters how many of these you're installing. If you install enough of them, it would really make a great case for electric cars.