Disclaimer: I have worked in the field of traffic calming and road safety engineering for over 30 years and have designed and reviewed schemes in dozens of local authorities across the UK.
In all this time, I have seen time and again that the single most effective thing we can do to make streets safer for pedestrians and cyclists is to slow down traffic. I have analysed collision statistics for hundreds of sites before and after the installation of speed humps and seen the remarkable impact that properly designed and maintained speed humps can have on reducing casualties and saving lives.
I know from experience that while education and enforcement are important, they are not enough on their own to change driver behaviour in the long term. To make a street safe, we need physical infrastructure that actually makes speeding uncomfortable, impractical, and ultimately impossible.
Speed bumps are the most effective and evidence-based tool we have for creating safe streets. They are not just an annoyance for motorists or a cosmetic addition to residential roads. They are life-saving interventions backed by decades of research and real-world data.
In this article, I will share what I have learnt over the years about the critical role that speed humps and bumps play in creating safe streets, and how they tie directly into the ambitious goals of Vision Zero and the 20’s Plenty movement that are reshaping our approach to urban street design.
The Science of Impact Speeds: Why Every Mile Per Hour Matters
The relationship between vehicle speed and pedestrian survival is not linear, it is exponential. This is the most important piece of evidence that underpins everything we do in traffic calming.
Research that is frequently cited by the UK Department for Transport shows that a pedestrian struck by a vehicle travelling at 30mph has only a 50% chance of survival. At 20 mph, that survival rate increases to 97%. To be clear: reducing speed by just 10mph transforms a coin-flip chance of death into a 97% probability of survival.
These are not abstract statistics, these are real people, real families, and real communities. The Transport Research Laboratory (TRL) has done some impressive biomechanical work that explains why this relationship exists. At higher speeds, the kinetic energy transferred to a pedestrian’s body during impact increases exponentially. A vehicle travelling at 30mph has more than twice the kinetic energy of one travelling at 20mph. When that energy is transferred to the human body, particularly the head and torso, the results are catastrophic.
Public health data backs this up. A study published in the British Medical Journal that looked at pedestrian casualties across several UK cities found that for every 1 mph reduction in average traffic speed, the frequency of collisions reduced by around 6%. The Department for Transport’s own collision statistics show that in 2019, before the pandemic changed traffic patterns, speed was a contributory factor in 25% of all fatal collisions. In built-up areas where pedestrians are most vulnerable, inappropriate speed is one of the leading causes of serious injury and death.
What makes these stats so powerful is their consistency across different studies, different countries, and different time periods. Whether you’re looking at London, Manchester, or Edinburgh, the relationship between speed and harm remains the same. This scientific consensus provides the foundation for evidence-based policy interventions – and it’s why speed humps, which physically enforce lower speeds, are so important.
Vision Zero and 20’s Plenty: Policy Movements Demanding Physical Solutions
The Vision Zero movement, which started in Sweden in the 1990s and has since spread around the world, is based on a simple but revolutionary idea: no loss of life on our roads is acceptable.
Rather than treating traffic deaths as unavoidable “accidents,” Vision Zero recognises them as preventable public health crises. The movement shifts the responsibility from individual road users to system designers, asking: how can we design streets that protect people even when mistakes happen?
20’s Plenty for Us is a similar movement that began in the UK in 2007. It advocates for 20 mph speed limits as the default in residential areas. The campaign has had remarkable success, with hundreds of local authorities across the UK introducing 20 mph zones and limits. Edinburgh, for example, implemented 20 mph limits across most of the city in 2016, and in 2023 Wales became the first nation in the UK to introduce a default 20 mph limit in built-up areas.
But, and this is the critical point I have learned over the years, signs alone are not enough. A road safety officer I used to work with at Bristol City Council, who were one of the leading authorities in implementing 20’s Plenty, put it perfectly: “We can put up all the signs we like, but if the road design still feels like a 30mph environment, drivers will still travel at 30mph. The physical environment must match the legal limit.”
It is supported by extensive monitoring data. Where 20 mph limits have been introduced with signage alone, compliance rates are typically around 20-25%. Average speeds may fall by 1-2 mph, which is a good start, but nowhere near the transformational change needed to make streets safe and reach Vision Zero targets. Where speed humps and other physical traffic calming measures have been added alongside the new limits, compliance is much higher and average speeds can drop by 5-10 mph or more.
Even the Department for Transport’s own guidance on setting local speed limits says this, stating that self-enforcing measures, those that make it physically uncomfortable or difficult to exceed the limit, are much more effective than enforcement through cameras or police presence alone. And this is where speed humps become not just helpful, but essential.
Physical Infrastructure is the Only Reliable Speed Enforcement
Speed humps are, in my opinion, the most honest form of traffic management. They don’t rely on driver goodwill, they don’t depend on police resources, and they don’t require behavioural change campaigns. They simply make it uncomfortable and impractical to speed. This reliability is their greatest strength.
Speed bumps and speed humps work in a very simple way: they create a vertical deflection in the road surface that, when driven over at speed, causes an uncomfortable jolt for vehicle occupants and potential damage to the vehicle’s suspension. Drivers quickly learn that slowing down is in their own interest. Unlike speed cameras, which can be switched off or moved, or police enforcement, which is resource-intensive and intermittent, speed humps provide 24 hour 365 day speed reduction.
The Transport Research Laboratory has done a lot of before-and-after studies of speed hump installation. Their research has shown again and again that properly designed speed humps can reduce average speeds by 5-10 mph and reduce the 85th percentile speed (the speed at which 85% of vehicles are travelling at or below) even more significantly. More importantly, they also reduce collisions. A comprehensive TRL study that looked at multiple sites found that speed humps reduced injury collisions by an average of 44%, with some sites seeing reductions of 60% or more.
This collision reduction has real-world impacts in terms of lives saved and serious injuries prevented. When I look at Department for Transport collision statistics for areas where comprehensive speed hump schemes have been put in place, the pattern is very clear: fewer collisions, fewer serious injuries, and fewer fatalities. The data speaks for itself.
One thing I have also found to be very encouraging is that speed humps don’t just slow traffic in their immediate vicinity. They create a psychological shift in how drivers perceive the entire street. When drivers encounter a series of speed humps, they begin to think of the street as a low-speed environment. This “self-explaining road” principle is well established in traffic psychology research, and it means that the benefits of speed humps extend beyond the humps themselves.
Speed Humps and Bumps: The Foundational Tool for Safer Streets
Like any traffic calming measure, speed humps are not a one-size-fits-all solution. Different designs are more appropriate in different contexts, and as a traffic engineer, I have had to specify dozens of variations over my career. Traditional speed humps, typically around 75-100mm high and 3-4 metres wide, are the bread and butter of traffic calming. They are well-suited to residential streets with 20-30 mph speed limits and can be installed relatively quickly. Speed cushions, which feature gaps to allow buses and emergency vehicles to straddle the humps, can be a compromise solution on bus routes or streets where emergency vehicle access is a concern.
Speed tables, which are essentially flat-topped speed humps, offer a different profile while still achieving the same speed reduction. These can be particularly useful at pedestrian crossing points, where the speed table brings the road surface up to pavement level, making it more visible and accessible to pedestrians. I’ve become increasingly impressed with cobbled speed bumps in recent years, particularly the quick-setting varieties. Traditional asphalt speed humps, whilst effective, can take a long time to install and often require road closures that are disruptive to local communities. Quick-setting cobbled speed bumps, like the ones sold under the Quicksetts brand, have proved a compelling alternative in my experience.
The system uses pre-formed cobbled units that can be laid in place rapidly, typically within a single day, and achieve full strength in hours rather than days. The aesthetic benefit of cobbled speed bumps is also significant. In conservation areas or streets where visual impact is a concern, cobbled humps can be much more sympathetic to the existing environment than stark asphalt humps. I’ve specified Quicksetts and similar products on several heritage town centres, where they have proved very effective at speed reduction while still maintaining the character of the area.
Implementation Best Practices: Getting Speed Humps Right
Speed humps are a simple but effective traffic calming measure, but they need to be implemented well to maximise their benefits and minimise their downsides. I have developed a set of principles over the years that help to achieve this. One of the first principles I always apply is that speed humps need to be spaced correctly. The spacing is critical because if humps are too far apart, drivers will accelerate to a higher speed between humps and then brake sharply when they approach the next one, negating the calming effect and creating noise and emissions issues. If they are too close together, drivers become excessively uncomfortable, and the whole point of the measure is compromised.
Secondly, I ensure there is clear advance warning of the speed humps. Drivers need to be made aware of the humps well in advance to avoid sudden, harsh braking, which can be dangerous. Road markings such as white triangles or “SLOW” markings can be used to reinforce this.
Third, I always consult with local communities and stakeholders before implementing speed humps. I have seen schemes fail politically simply because the community wasn’t properly consulted or engaged. On the other hand, I have seen communities that were initially opposed or sceptical become the scheme’s strongest advocates once they could experience the benefits for themselves. A road safety officer at Camden Council, which has implemented extensive traffic calming, told me: “The key is helping residents understand that there will be temporary inconvenience during the installation process but that it leads to permanent improvements in safety and quality of life.”
Fourth, after installation, I recommend monitoring traffic speeds and volumes to ensure the speed humps are having the desired effect. Sometimes, additional adjustments are necessary, perhaps adding more humps or tweaking the existing profile.
Finally, maintenance is often overlooked but is crucial. Speed humps and bumps need to be inspected and maintained regularly to ensure they remain effective. Worn or damaged humps can be less effective and even create hazards. The modern pre-formed cobbled speed bumps have a distinct advantage in this regard—they are typically much more durable and easier to repair or replace than traditional asphalt speed humps.
The Main Objections: Unravelled
Not everyone is convinced by the evidence on speed humps, of course. I have heard all the objections, and they come up repeatedly in community consultations. They will damage our vehicles, increase emissions, delay the fire brigade, make more noise, and be incredibly uncomfortable for passengers. I find the vehicular damage objection particularly ironic, given that a significant cause of that damage would be speeding, the exact behaviour that humps are intended to prevent. Properly designed speed humps, traversed at the appropriate speed, should pose no risk to vehicles. The discomfort objection is similarly circular: yes, speed humps are designed to be uncomfortable at 30 mph, but perfectly comfortable at 20 mph, which is the whole point.
The emissions argument is more nuanced but ultimately not a showstopper either. It is true that individual vehicles may emit slightly more pollutants when decelerating and accelerating at speed humps, but this is more than offset by the overall reduction in traffic speeds and volumes, which leads to improved air quality. And, of course, the public health benefits of reducing collisions by even a fraction are so great that they far outweigh any marginal increase in emissions.
Emergency services are a legitimate concern, which is why there are designs like speed cushions that allow emergency vehicles to pass with minimal delay. The London Fire Brigade has studied this and found that properly designed traffic calming, including speed humps, caused minimal delays overall and greatly improved community safety.
The noise issue is a valid concern in some cases, particularly with heavy vehicles. However, modern designs, including the cobbled speed bumps and speed tables with appropriate profiles, can mitigate noise impacts. And again, the noise of occasional vehicles traversing speed humps is often outweighed by the noise reduction from lower overall traffic speeds.
In short, there are no showstoppers here. None of the objections, even when valid, are fatal to the case for speed humps in most situations. The benefits far outweigh the downsides, which can often be mitigated with thoughtful design and implementation.
Conclusion: The Best Tool in Our Arsenal
After thirty years in this business, I am more convinced than ever that speed humps are one of the most valuable tools we have for making streets safer. They are the physical embodiment of Vision Zero, the enforcement mechanism that makes 20’s Plenty more than just an aspirational speed limit. They are the tool that turns the exponential curve between speed and harm into a line of lives saved.
The evidence is clear: the Department for Transport statistics, the Transport Research Laboratory research, the public health data, the on-the-ground experience. It all points to the same conclusion. Reducing speeds saves lives, and speed humps reduce speeds more reliably than any other measure we have.
I am encouraged by the developments in the field, from the quick-setting cobbled speed bumps that are so much faster to implement to the growing political will to prioritise the safety of pedestrians over the convenience of motorists. And I am heartened by the success stories we are seeing from local authorities that are leading the way with comprehensive traffic calming measures.
But we have a long way to go still. Every residential street should be a 20 mph environment backed up by physical infrastructure. Every school zone should have speed tables at crossings. Every high street should prioritise the safety and comfort of pedestrians over the flow of traffic. The technology and the evidence are both there. What we need now is the collective will to act.
Speed humps and bumps are not a panacea. They are not glamorous or headline-grabbing or award-winning design. But they work. They save lives. And in the end, that is what matters. When I look at collision data from streets where we have implemented a comprehensive speed hump scheme and see the drop in serious injuries and fatalities, I am reminded why we do this. Behind every prevented collision is a life unchanged by tragedy, a family not torn apart by grief, a community made safer.
That is the promise of speed humps: not comfort or convenience but safety. And in our built environment, safety must always come first. The foundational tool for safer streets is not high-tech or complicated. It is a simple raised surface that makes speeding uncomfortable and slow speeds natural. It is the speed hump, and it’s time we recognised it for the life-saving tool that it is.
