Do speed bumps cause more deaths than they save?

Question

After a few speeding incidents in a residential neighborhood, some residents will clamor for speed bumps.

In case your municipality does not have one, here is a picture of a speed bump (also AE sleeping policeman, BE road hump, road bump):

From a Washington Post article

A Connecticut government site has considered damage to vehicles, and this anti-speed bump flyer cites the difficulties with emergency vehicles navigating speed bumps, replete with pull quotes from unnamed emergency personnel. It also cites "well researched reports," but alas, the link is dead.

Do the speed bump detractors have any merit? Or are they off track / up in the air / (insert appropriate pun here)?

I believe the dead link is probably trying to get to a copy of [Deaths Expected from Delayed Emergency Response Due to Neighborhood Traffic Mitigation](http://americandreamcoalition.org/safety/bowman.doc), Ray Bowman, Submission to the City Council of Boulder, Colorado, 1997. [Microsoft Word doc] — Oddthinking, Oct 01 '11 at 02:17
Anecdotal: Last winter I hit a speed dump at night with my bicycle, hit the floor, lost my glasses, had a cut in the face and needed a surgeon with needle. I haven't seen it, and was travelling with 15-20 km/h. But to cause death - no, nearly impossible. — user unknown, Oct 01 '11 at 05:49
@User: Wait. You banged your head against the ground, while travelling 15-20 km/h, but you conclude there is no chance of death? Sounds awfully plausible to me. In any case, this isn't the sort of death the OP is asking about, but the risk for emergency services vehicles and the like. — Oddthinking, Oct 01 '11 at 07:34
@Oddthinking: The speed bumps don't *cause* the deaths. If an emergency vehicle is needed, then the injury/emergency had already occurred without being caused by the speed bump. While it might be noted that speed bumps slow down vehicles, the bumps are generally only placed in residential areas where there are unobservant pedestrians and cyclists who are likely to be injured by speeding vehicles. — oosterwal, Oct 01 '11 at 16:28
@oosterwal, I think the point here is clear. We can use the economists' approach: How do the number of deaths compare if everything else was equal with the only change being the existence of the speed bumps? — Oddthinking, Oct 01 '11 at 18:57
@Oddthinking: I don't disagree with that. It's important that the detriment towards emergency vehicles be compared fairly against injuries caused by speeders. — oosterwal, Oct 01 '11 at 21:39
Thanks for the paper reference, @Oddthinking. I am not completely discounting Bowman's paper, but this may be a little too much economist-approach-assumptions, with attendant hand-waving. I would really like to see a side-by-side comparison of two similar-sized towns where one added speed bumps and the other did not. Or maybe compare the same town before and after speed bumps. — rajah9, Oct 01 '11 at 21:56
@rajah9: Nodding my head in vehement agreement. (With you, too, oosterwal!) — Oddthinking, Oct 02 '11 at 12:14
@Sklivvz answer provoked another thought: Often public health interactions aren't measured in lives saved, but years of quality life (or some such). One healthy 10-year-old saved from an accident may be considered worth more than two 80-year-old stroke victims saved from serious symptoms. — Oddthinking, Oct 02 '11 at 12:26
@Oddthinking the problem is that there are exactly zero documented deaths from slow ambulances due to speed bumps. Speed bumps don't *force* vehicles to go slow. Also, in the spirit of the manifest absurdity of this "theory", I would like to propose a variant: yes, ambulances slow down, hence they hit less pedestrians. — Sklivvz, Oct 02 '11 at 12:39
+1 ROFL for the variant. Blast those ambos speeding around everywhere like lives depended on it! — Oddthinking, Oct 02 '11 at 13:07
@Oddthinking: a) It was not such a smooth bump. b) the position is behind a curve, where few cyclists would reach a significant higher speed. — user unknown, Oct 02 '11 at 19:50
I don't think that speed-reducing devices end up causing any deaths, but the argument should be: "how far do we go in preventing vehicle deaths?" Obviously, fitting all vehicles with governors that cap the speed at 1 mph or kph would save an enormous number of lives, but should we do it? Any change that reduces lives should not be enacted unless it fits an argument for reasonableness. In the US, I have read that half of all traffic fatalities involve alcohol. The solution is simple: make alcohol illegal. Been there, done that. People weigh and decide what they will accept. Risk is unavoidable. — , Oct 08 '15 at 23:05

score 18 · Answer 1 · edited Jan 10 '21 at 13:15

18

^source

Let me oppose science to political propaganda and flyers:

Objectives. We evaluated the protective effectiveness of speed humps in reducing child pedestrian injuries in residential neighborhoods.

Methods. We conducted a matched case–control study over a 5-year period among children seen in a pediatric emergency department after being struck by an automobile.

Results. A multivariate conditional logistic regression analysis showed that speed humps were associated with lower odds of children being injured within their neighborhood (adjusted odds ratio [OR] = 0.47) and being struck in front of their home (adjusted OR = 0.40). Ethnicity (but not socioeconomic status) was independently associated with child pedestrian injuries and was adjusted for in the regression model.

Conclusions. Our findings suggest that speed humps make children’s living environments safer.

—source

The 20 mph zones have successfully reduced accidents by about 60 per cent and vehicle speeds by over 9 mph.

—source — the study includes speed bumps specifically

According to wikipedia there is one retracted statement by a London ambulance driver that speed bumps may affect the effectiveness of emergency services—I cannot verify that source because the link is dead—however, skeptically speaking this is a no-brainer.

Suggesting that it is better to have more injuries and the emergency services arrive faster is... not smart.

Speed kills, speed bumps save lives

edited Jan 10 '21 at 13:15

Glorfindel

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answered Oct 02 '11 at 09:10

Sklivvz

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I'm not happy this answers the question. It certainly shows that in practice speed bumps reduce vehicle speed and accidents with children. But that wasn't in contention. And I strongly suspect you are right that the payoffs are generally worth it. But, can we simply dismiss the claim as "not smart"? Using reductio ad absurdum, a speed bump placed in the driveway of an ambulance bay is probably not going to have a net benefit. Is there any way we can meaningfully quantify the cost? – Oddthinking Oct 02 '11 at 12:23
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@Oddthinking: I have demonstrated that having properly placed speed bumps reduces the need for ambulances, both by reducing the *number* of accidents and the *gravity* of accidents. I've reviewed all the relevant literature I could find. *There is no single scientific claim that slowing down ambulances has any overall measurable effect.* Give me something to work with here... the evidence only points in one direction :-) – Sklivvz Oct 02 '11 at 12:36
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your statement "speed kills" is incorrect. It's the incorrect application of speed that kills :) But yes, ambulances (in my experience with them) tend to drive slowly, carefully, when they have a patient on board, so a speed bump won't do much (as those tend to be designed to slow down higher speed traffic). Of course a poorly designed speedbump may cause trouble, but not speedbumps by definition. – jwenting Oct 03 '11 at 09:06
@Sklivvz, thank you for your answer. This is one aspect of what I was looking for: same town, before and after speed bumps. The data are striking. – rajah9 Oct 03 '11 at 19:22
"Counterintuitive" would probably be a better rejoinder than "not smart." The former is simply an observation. The latter seems vaguely pompous. – Robert Harvey Jan 12 '21 at 16:12

score 7 · Answer 2 · edited Dec 27 '13 at 15:50

Partial Answer

This doesn't answer the question. I offer it as partially-digested research that may be useful to others generating a full answer.

In August 1997, the Montgomery County Fire and Rescue Commission produced a report called "The Effects of Speed Humps and Traffic Circules on Responding Fire-Rescue Apparatus in Mongomery County, Maryland."

They conducted an experiment to see how much effect speed-bumps had on their response times. The results are complex:

The amount of delay was found to be dependent upon three factors - vehicle type/size, type of traffic calming device, and driver discretion regarding speed.

For some situations, the delay "is equivalent to responding from a station .05 mile per speed hump further away from the incident location along an unimpeded route." (For the civilised world, that corresponds to about 80 metres.)

Note: 80 metres at 50 km/h (which is compatible with humps) is less than 6 seconds.

So, yes, there are — as we might expect — real delays. But the real question is "how many lives are lost due to this delay?" so we can compare it with the figures in Sklivvz's answer. Neither Sklivvz nor I have found an answer to that question. Is it out there?

It is hard to prove there has been no research on a topic — especially as an amateur in the field. One way to address this is to show some experts have looked and not found any.

One report in a 2008 Road Safety seminar hosted by the UK Deportment for Transport, Behavioural Research in Road Safety 2008 Eighteenth Seminar was a prelimary study (including surveys of drivers) called "Risk and the driving of emergency vehicles" by Tomás Walsh, Barbara Hannigan and Ray Fuller.

Road humps Speed humps and other road features designed to restrain speed, such as speed tables and cushions, are recognised to cause delay, but the trade-off in reductions in road accidents is also admitted:

They do make a claim that there is no evidence to help us answer this question:

It might be noted that there does not appear to have been any analysis published which attempts to estimate the size of this possible trade-off.

Consistent with that understanding that the data has not been collected is a 2003 letter from Peter Bradley, Chief Executive of the London Ambulance Service.

The tone of the letter is generally warning of the risks of speed bumps in slowing response times:

This Service believes that it could probably save more lives if the overall traffic flow were to be improved. Just among the 5000 cardiac care victims that we try to resuscitate this could possibly save about 500 lives. In addition a minute gained in reaching other life threatening cases could potentially save hundreds of lives.

However, it also admits that there is a dearth of relevant information:

We believe there have been a number of studies relating to ‘speed humps’ but at this time the LAS is not aware of any significant UK-based report that has made any scientific study into the overall effects of speed humps, including their impact on ambulance response times; the potential consequences of delayed responses by emergency vehicles to ‘life threatening’ situations; and their effect on the comfort of patients being conveyed to hospital.

We would welcome the opportunity to be involved in any such research if it were to be commissioned.

Apparently there is less correlation than one would think between the EMS times and survival rate. Why? Because it matters only in particular cases like cardiac arrest:

Study objective
The first hour after the onset of out-of-hospital traumatic injury is referred to as the “golden hour,” yet the relationship between time and outcome remains unclear. We evaluate the association between emergency medical services (EMS) intervals and mortality among trauma patients with field-based physiologic abnormality.

Methods
This was a secondary analysis of an out-of-hospital, prospective cohort registry of adult (aged ≥15 years) trauma patients transported by 146 EMS agencies to 51 Level I and II trauma hospitals in 10 sites across North America from December 1, 2005, through March 31, 2007. Inclusion criteria were systolic blood pressure less than or equal to 90 mm Hg, respiratory rate less than 10 or greater than 29 breaths/min, Glasgow Coma Scale score less than or equal to 12, or advanced airway intervention. The outcome was inhospital mortality. We evaluated EMS intervals (activation, response, on-scene, transport, and total time) with logistic regression and 2-step instrumental variable models, adjusted for field-based confounders.

Results
There were 3,656 trauma patients available for analysis, of whom 806 (22.0%) died. In multivariable analyses, there was no significant association between time and mortality for any EMS interval: activation (odds ratio [OR] 1.00; 95% confidence interval [CI] 0.95 to 1.05), response (OR 1.00; 95% CI 9.97 to 1.04), on-scene (OR 1.00; 95% CI 0.99 to 1.01), transport (OR 1.00; 95% CI 0.98 to 1.01), or total EMS time (OR 1.00; 95% CI 0.99 to 1.01). Subgroup and instrumental variable analyses did not qualitatively change these findings.

Conclusion
In this North American sample, there was no association between EMS intervals and mortality among injured patients with physiologic abnormality in the field.

Thank you for citing this data. I wonder if you might know this about the Montgomery County data. Is 80 meters for the average trip, or for each bump? The pattern that I see in my adopted North Carolina is no speed bumps in the main roads and more speed bumps on residential areas with through streets. An ambulance coming to my neighborhood might only see 3 bumps on the entire trip (only a few miles to the fire & rescue station) and those at the very end. — rajah9, Oct 03 '11 at 19:25
Thanks, @Oddthinking. I visited a retirement community recently and observed that there are no speed bumps (only large crosswalks with herringbone patterns). I wonder if planners take this into consideration and put speed bumps in residential areas with young children and flat, visual markers in residential areas with older adults. The younger families need the cars to slow down, but the older families need faster ambulance response times. — rajah9, Oct 04 '11 at 13:48
@rajah9 - More likely there is benefit to society in preventing children from dieing they have yet to contribute taxes to the government. Where the old people are just collecting pensions so if they die from being hit by a car then the governemt no longer has to spend money on them. Where is the outrage for the old farts! — Chad, Oct 04 '11 at 18:15
@chad or far less cynically planners presume anyone that survived into old age is probably smart enough to *not* run out into the middle of the street with an incoming vehicle while chasing a ball, and thus there is less risk of fatality with them there there is in residence with young children. Planners may then choose not to add a feature that is generally deemed annoying by drivers and inconvenient if it's unlikely to save lives the way it does in residential areas with young children. — dsollen, Jan 11 '21 at 16:39
A suggestion on where to look for more data: Try going up--specifically, survival rates based on what floor one is on. I remember seeing data that it mattered, but I do not recall anything about the size of the effect. — Loren Pechtel, Jan 12 '21 at 02:46

Do speed bumps cause more deaths than they save?

2 Answers2