Speed Bumps are not effective "traffic calming" but an ineffective "Band-Aid" for poorly designed streets. Examples of more effective ways to calm traffic

A few days ago I tweeted about how speed bumps are used in the UK as a band-aid on streets which should have no through traffic. This perhaps requires a little more explanation.

No-one likes speed bumps
Speed bumps are unpopular everywhere. There are claims that they delay emergency services, even that they can injure some people transported by ambulance. Speed bumps cause damage to cars and lead to drivers slowing down to cross the bump before accelerating, which increases exhaust emissions and noise pollution. What's more, speed bumps are very unpleasant to cycle over and can cause danger to cyclists.

Most speed bumps shouldn't exist
Sadly, speed bumps seem to have become synonymous with traffic calming in many peoples' eyes. The problem with installing speed bumps as traffic calming is that the "solution" doesn't match the problem. Rather than attacking the cause of traffic problems, especially on residential streets where problems are typically due to their being used by through traffic, traffic is allowed to continue while an attempt is made to regulate speed by means of speed bumps. This approach has very serious limitations.

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Assen barely uses speed bumps at all
The city where we now live provides many good examples of cycling infrastructure, road and residential street design. We operate cycling infrastructure study tours from this location in order to demonstrate these concepts. In comparison with a British city of a similar size, Assen has very few speed bumps. See the photos below for examples both of poor and good practice

Bad examples
First the bad examples. Standard disclaimer: These photos and a video demonstrate where "traffic calming" is ineffective. Don't copy anything from them. Click here to go straight to the good examples.

An example from the UK. In an attempt to reduce speeds, seven speed bumps have been installed in a street of less than 500 m. However the problem with this street is the through traffic and these speed bumps do not address that problem. Using this street allows motorists to avoid a longer journey with traffic lights and is a rat-run especially during rush hour.

Another example of bad practice in the UK. This street has six speed bumps in 500 m but again becomes a rat-run during rush hour because it accommodates through traffic. The problem is exacerbated by allowing bidirectional usage when the street is so narrow. I once had to push my daughter off her bike between parked cars along here because a driver heading towards us at excess speed clearly had no intention of slowing.

Speed bumps are sometimes combined with restrictions (horizontal traffic calming) such as that shown here. But these also do not address the problems caused by allowing through traffic. Note that this street in London has both a 20 mph speed limit and is posted as a through cycle-route. This doesn't mean that conditions are good for residents or for cyclists as you can see from the video below.

Residents of Gillespie Road in London are campaigning for better conditions, using video of the rat-running traffic in their street. No-one should have to live with behaviour like this on their doorstep. I wish them luck with their campaign.

Speed bumps are not only used in obvious residential streets in the UK, but also sometimes on through roads like this. The road looks like a race-track but the speed bump requires slowing to around 10 mph. This bump rather took me by surprise on my last visit to the UK when I drove here in the dark at the posted speed limit of 30 mph. This is again bad design. There is no reason why drivers are expected to slow sharply at this point. Locals will learn about this. Otherwise it is unpredictable.

Good examples

Now for some good examples, all of which are residential streets in Assen which don't have a traffic problem. Assen has almost no rat-running. In the case of newly built areas, opportunities to take short-cuts though residential streets were designed out. In the case of older areas they have been re-designed out. Streets are "calmed" by means of reducing traffic and by designing streets which do not encourage high speeds, not by causing motorists to have to abruptly slow for obstacles.

If you would like to copy this success, rather than risk losing the context of these examples "in translation", we suggest a study tour in which you can be shown how these examples and others work.

30 km/h residential street in a 1970s suburb. While this is at times a busy through route by bicycle, there is no through route here for motor vehicles so motor traffic is restricted to residents and visitors.

50 km/h road in a 1970s suburb. There is more traffic here than on the 30 km/h street, but the traffic here also is residents and visitors only. There are no through routes by motor vehicle anywhere in this suburb and therefore there is no through traffic. Note raised table for the pedestrian and cycle-crossing. 

1970s suburb, brand new asphalt. The surface is suitable for high speeds, but the road layout is not. This is a non-through route. A cul-de-sac with no traffic other than that of the neighbours. Children play safely on the street here.

On the left, an example of a street in a newly built suburb. The yellow street on the left has been designed to encourage low speeds both by choice of surface material and by eliminating straight lines. At the same time, the white cycle-bridge makes cycling more attractive by providing cyclists and pedestrians with more direct journeys than are possible by car.

Retro-fitted junction between residential streets in a 1950s suburban area. The entire junction is a raised table. Note bollards used to encourage drivers not to cut the corner.

The reason why streets in a 1950s suburb do not suffer from rat-running is that the majority of the streets have been made into an elaborate one-way system specifically to break up through routes. The intention was not to make cycling difficult and therefore cyclists are always excepted from the one-way system. All the one-way streets in Assen serve to reduce motor traffic and they are therefore not comparable with those in the UK and other countries.

Another example of a one-way street in an older residential area in Assen. The one-way system is used to eliminate through traffic, except by bicycle.

Smoothly raised "roundabout" junction between residential streets in an older area. This makes it obvious to drivers that they should not speed, while causing little if any problem for cyclists.

The Netherlands has the most extensive network of low speed streets in the world. Almost all residential streets in Assen (and across the Netherlands) have 30 km/h speed limits. However, it's important to note that the calm nature of these streets is due to the removal of traffic more than it is due to the speed limit. Merely posting a lower speed limit is not effective.

This residential street is close to the city centre and perhaps attractive to people trying to avoid parking fees. Parking bays are provided for residents. The car on the left is not legally parked. Read more about residential car parking in the Netherlands. This is one of Assen's rare speed bumps. It's smooth to cycle over through not ideal with three wheels.

As we get very close to the city centre, where drivers would find parking on residential streets to be desirable, parking is for residents only (zone 6). The blue sign with a red bar bans on-street parking from that side of the road. The allowed side of the road for parking alternates, and this emulates the planned meandering road as seen in the newer suburbs.

In 2009, this obvious through route in a residential area had an obvious speed bump with cycle-bypasses. In itself, this is reasonably well designed. However, it was not necessary because this street does not actually suffer from much through motor traffic. See the next photo.

By 2012 the bollards had been removed and the speed bump had been made smoother. In reality, while this is a main route for cyclists (it continues as a bicycle-path from the point ahead with the circular blue sign) there is very little motor traffic here. Through traffic is removed by the one-way streets elsewhere. Note that while this street is one of the rare places in Assen where cyclists "share" the street with buses there is no bus-stop bypass.

People often mistakenly believe that the tiled surfaces of Dutch roads are historical. Actually, they're often very modern. This photo shows a street being transformed from wide asphalt to narrower tiled surface with off-street car parking. Read more about residential car parking.

A street which was transformed slightly earlier than the example in the last photo. Note that this is part of a one-way system which excludes through traffic.

In an older residential area, one of the narrowest streets in Assen. This is again part of a one-way system which excludes through motor traffic. By excluding through motor traffic, conditions can be made good for walking and cycling even on the narrowest of streets. Note how parking is allowed on one side of the street only. This alternates, emulating the planned meandering road as seen in the newer suburbs.

We've demonstrated these ideas to study tour participants for many years. In this example I'm explaining about one-way streets in Assen on a study tour. On the next Study Tour (September) we will again demonstrate a variety of residential street treatments.

Not everything is perfect in the Netherlands
While the Netherlands leads the world in such things as calming of residential streets, that does not imply that everything here has equal value. The Netherlands is a work in progress and problems can be found here too. These two examples are of residential streets in Assen in which there are problems, though these problems are at a much lower level that those illustrated by the British examples above:

A plastic doll, Victor Veilig, is requesting that drivers using this street should slow down. That a resident felt the need to buy this doll and install him on the street is an indication that all is not well.

Planters used as horizontal traffic calming. This street is not massively attractive to through traffic because it parallels a much more suitable road. However, these planters would not have been installed unless they were believed to be necessary and that indicates not all is well with this street. 

Even the relatively smooth and well designed speed bumps in Assen cause problems for some users. Any bicycle with more than two wheels, such as this machine being used by a person with a disability person, can't fit around the side of the speed bump. That problem is magnified when there is also an illegally parked car.

A car crash so quiet that we didn't know it had happened

On Monday morning there was quite a serious car crash just 70 m from our home. We didn't know about it until later in the day when it was reported on the local news. This may seem like an unlikely story, and you may wonder how it could be possible that we would miss such a thing so close to our home, but this actually makes a good example of how successfully Dutch residential areas are insulated from the effects of major roads, even when they pass nearby.

The crashed car, by the closest bus-stop to our home. Photo: RTV Drenthe.

The huge road on which the crash took place. The car in the photo above is in the same position as the bus in the photo below.

Our home is on the left of the Google Maps measurement tool, the crashed car was on its right.

The road on which this crash occurred is the ring-road of Assen. This has a 70 km/h speed limit (43 mph), this being the highest speed limit that you will generally find is allowed on a road within a city in the Netherlands. The relatively low speed for what is not far off an urban motorway does of course help to keep noise levels down, but you'll also note that the photos above show a noise barrier alongside this road. The barrier is extremely effective at reducing noise, and also makes it next to impossible to see the road. This is why it was possible that we didn't even know the crash had happened until later in the day.

Cyclists are often unaffected by crashing cars

The cycle-route skips past the traffic
lights and goes nowhere near the road

The cycle-path which we use to ride into the city is visible on the image from Google Maps above. It passes almost exactly under where the crash occurred so cyclists who were riding here even as the crash occurred may well not have noticed it happening, and will not have been put in danger.

By using this tunnel, cyclists not only cycle in a safe and almost entirely noise free environment but also skip past a set of traffic lights.

The tunnel and noise barrier between them reduce danger for cyclists, reduce noise and also reduce how often cyclists have to stop on their journeys. These factors add together to make cycling more pleasant and relaxing and also to offer the prospect of faster and shorter journeys if you travel by bike.

Measuring noise levels - how effective is the barrier?
It's quite straightforward to measure the effect of a noise barrier if we have the right equipment. The photo on the right shows my SPL meter measuring the sound level in our front garden, a mere 50 metres from the road. The glimpse of blue in the centre top of the photo is as much as we can see of the noise barrier, which is otherwise completely invisible due to trees. My meter barely ever registers any noise here. Set on the lowest possible range of 60 dBA, the needle very rarely moves from the -10 dB setting due to traffic noise, indicating a level which barely ever rises above 50 dBA. Birds in trees nearby make a subjectively louder sound than traffic noise. 50 dBA is the sort of level sometimes described as being equivalent to an "average home interior" or "moderate rainfall"

My SPL meter barely moves
on this side of the barrier

By comparison, on the other side of the barrier I have to adjust my meter's range so that it is not overloaded by the sound. When standing there, the meter often shows figures of 82 dBA or higher as I am passed by cars, and can peak higher yet for buses, trucks and motorbikes, so it would appear that our front garden is at least 30 dB quieter than the road-side.

The inverse-square law does not apply
Readers with a physics or maths background will probably have thought of the inverse-square law by now. According to the inverse-square law, you would expect that a ten times difference in distance from the source of a sound would bring a 20 dB difference in sound level, which is a good part of what I have measured. However, you have to be careful with that assumption in this case. The inverse-square law applies only for measurements in a free field and with a point source.

Noise from aircraft travelling overhead is attenuated according to the inverse-square law because these conditions apply, but when considering noise from motor vehicles on roads we usually have neither a free field (airborne sound bounces from the road more than it propagates through it) nor a point source. A busy road with many cars on it (such as during rush-hour when I made my measurements) more closely approximates to a line-source than it does to a point.

Noise from roads is so pervasive in large part because it is not attenuated by distance to the extent that you might hope it would be.

Besides, if you need further evidence of the effectiveness of the barriers, I should point out that my meter still measures only slightly over 50 dBA even if I stand very close to the quiet side of the barrier, when my distance from the noise source (cars on the road) is only about double that of standing on the noisy side of the barrier.

Barriers also reduce air pollution
It has been shown that air pollution from motor vehicles is also reduced in the local immediate downwind area behind noise barriers. This is due to the pollution being lifted to a higher level where it is blown away more quickly. We breath cleaner air as a result of the noise barrier.

And help to encourage neighbourlyness

Children play on our street because it's
quiet and traffic free, This is normal
in Dutch residential streets.

This is all part of creating a pleasant residential environment. Research has found that streets which are quiet (both in terms of through traffic and noise) lead to better relationships with your neighbours.

Quietness is not unusual in the Netherlands
On our study tours we demonstrate the surprising quietness of Dutch residential areas and also how even motorways with vehicles travelling at 130 km/h (80 mph) now cause comparatively little noise nuisance.

Take a look at the other side of the road
The other side of the main road has a through cycle-route which is protected by the same kind of wall.

Solving the problem of pavement car parking in residential streets

Ruysdaelstraat in Assen in 2009

Ruysdaelstraat in 2012

Residential areas frequently suffer from problems caused by car parking. This can take the form of cars parked on the road getting in the way of other drivers, cars parked on the road causing cyclists to have to swerve around parked cars (can be dangerous especially for less confident cyclists) or cars parked on the pavements (sidewalks) causing nuisance and danger for pedestrians.

Detail of parking space. Note that the
kerb is angled. It's designed to enable
driving over only at a slow speed.

Such problems can be addressed by redesign of the street, and there are many good examples of this in the Netherlands, including on many streets in Assen such as that shown above. The first picture, from Google Maps, shows how the street used to look up until very recently. The second was taken today as I cycled along this street.

These houses and the street which they are built alongside, date from the 1930s but existing trees on just one side of the road were recently taken up and replaced with trees on both sides of the road combined with parking bays.

Note that while the direction of motorized traffic was changed recently, this street has been one-way except for cyclists for some years. Routes for cyclists are unravelled from those for drivers. This is a useful through route with a bike, but not with a car. This makes yet another example of how segregation of modes is achieved without building cycle-paths.

Other examples:

This street in the newly built suburb of Kloosterveen uses the same design to keep cars off  a series of streets which together form a direct route only by bike. This is the only photo in this blog post of a new development.

A different way of achieving a similar result can be to use concrete setts through which  the grass can grow.

In some areas, bollards are used to control parking, This is a one-way street with cyclists excepted.

The same street, showing how there are again angled kerbs to climb a low speed in order to park one's car.

Sometimes, parking bays are built on-road, alternating from one side to another. This is again a street which makes a good through route for cyclists (linking up with the bridge shown in this video) but which goes nowhere for drivers. In this case, the permitted side of the road for parking alternates, which makes the road meander and serves to slow traffic.

All the streets in these photos have 30 km/h or lower speed limits. In this case with a smooth speed bump with a cycle by-pass on both sides and parking bays for cars on one side of the street. Again this street does not offer a useful through route by car.

The only street in Assen converted into a Woonerf. Here the speed limit is walking pace. Note that cars can park on one side only.

An older treatment showing parking bays on both sides of the road to achieve a similar result.

Another example of cars parked between the road and the pavement (sidewalk)

The bays can be made quite attractive, improving the green look of a neighbourhood rather than  resulting in residential areas looking like car parks.

Work continues right now on the process
of transforming older residential streets

This process of improvement is continuing right now on streets across Assen as more residential streets get this treatment. Where possible there is always enough car parking so as to avoid parked cars becoming a problem. This is how drivers are persuaded not to leave their cars in places which cause problems for cyclists and pedestrians.

In the Netherlands, people are not discouraged from driving by providing inadequate car parking spaces (as has been done to disastrous effect in the UK) but are provided adequate spaces to park their cars while cycling is made attractive by making cycling routes more convenient.


Dutch homes provide secure cycle parking by law but most other countries do not. In either case it's a good idea to use a secure bicycle lock on any parked bicycle.

The highest modal share for cycling in the world works due to carrots, not sticks.

Retrofitting sanity to residential streets - Woonerven

Explanatory captions on this video are visible only if you view it on a computer and not on a mobile device.
The Woonerf or "Living Street" is a design for residential streets which puts people first. I've written about streets designed and built specifically as woonerven before, but the streets in this video are different. This time you see some of the many streets in the Netherlands which originate from long before the advent of the woonerf, but into which these principles have been incorporated.

The speed limit is "walking pace", but the main reason that such streets are pleasant to live in is that they simply don't work as through roads so the only vehicles you'll see here are those which belong to people who live in the street. You're not going to make any journey quicker by driving through here instead of on the main road. Note that they're also not through routes by bicycle. A woonerf is for living in. It's not a main route for anyone.

Often, people complain that Dutch solutions to creating a cycling and people friendly street-scape might take too much room. This is a myth. In these examples, much has been achieved in very narrow streets and without re-arranging existing buildings. The important thing is to distinguish between where people live and where suitable places are for through journeys to be made.


A correspondent in the comments wondered about how nice it might be if cars that people owned were parked at the edge of the development and therefore not in the streets where people live. This is difficult to achieve with housing which already exists, but there is an example of a newer (1980s) development in Assen where this was done:

Grotere kaart weergeven
The problem with this is that people like to be able to see their car from their home. Newer developments have not copied this style.

Road noise, cobbles and smooth asphalt

The red line to the West of the city is the motorway. That
which runs from the South to the North East is the railway.
Another blog posts shows the noise levels at the location
of the upper blue cross

The noise map on the left shows noise levels in Assen. From the 1970s onwards, research lead to several generations of quieter surfaces for Dutch motorways so that the noise pollution from them is less than it could be, and that it does not spread widely. There are also lower speed limits on Dutch motorways where they pass near residential areas, and barriers alongside them to block the sound.

The red cross on the noise map of Assen is the position of noise barriers featured before on the blog. The blue crosses are where we've stood with people on Study Tours to demonstrate that while the A28 motorway (the main motor vehicle route North-South) is the noisiest road in the city, you can still be remarkably near to it without having to raise your voice to be heard. This is actually a remarkable difference from the thunderous roar which is normal for people living near some British motorways, though as you can see on the map, they are still a greater source of noise than anything else.

However, noise is also used in another way. While motorways have been made quiet, many residential streets do not have these super smooth quiet surfaces. Many of them have rather rough cobbled surfaces as shown in this photo. It's traditional, and looks really nice.

Such a surface is also noisy to drive a car on. I have never seen anyone say that it is deliberately kept this way, but it is interesting that in the Netherlands if you go on a long journey in a car then the road noise inside the car is relatively low compared with the noise inside when you come off the motorway and drive much slower on residential roads. The opposite problem occurs in other countries, and is sometimes pointed out as a reason why drivers might speed when they come off the motorway - because they've become used to the noise level while driving faster.

These cobbled streets are often on cycle routes. Cycle routes on roads frequently don't follow the same line as car routes. Rather, these "shared" roads have very few cars on them, because the roads have 30 km/h speed limits and the direct through route is only usable by bike or on foot. Often one way restrictions applying only to motorized vehicles are used to make sure that a cyclist using a back street won't see motorists competing to also use it as a through route. "Rat-running" is virtually eliminated.

Forcing drivers to take different routes to the direct routes taken by cyclists is a way of keeping cyclists safe from drivers without cycle paths.

However, because these cobbles are rough, they're not the best surface for cycling on. There is now a new type of cobble, as shown on this "bicycle road" in Assen (A "bicycle road" formally allows cycles in preference to drivers).

These special square edged cobbles have the aesthetic of the traditional type, but they give a smoother ride, nearly as smooth as asphalt or concrete. This bicycle road forms the most direct route into Assen from a new suburb (as seen here and here). The special cobbles are a little more expensive, but considered to be worth using because they keep the historic centre of the city looking good, while also giving cyclists a better than average, more comfortable, surface on which to ride.

In the past, cycle paths in the Netherlands were surfaced with cobbles, and sometimes these were not pleasant to ride over. Replacing older cycle paths is a continuous process and many have now been resurfaced. Modern surfaces are either very smooth asphalt, as in this photo, or concrete.

It's not uncommon for cycle paths alongside a road to have a smoother surface than the road itself. This is the case for a good part of the route between here and Groningen, where the cycle path is concrete while the road is asphalt. The concrete surface offers not only smoother riding, but also lower rolling resistance and higher speeds for cyclists vs. riding on the road. You also see this done quite deliberately in the countryside.

I had always assumed that the cobbles were laid down by hand until I saw this (but having started here talking about noise pollution, I recommend that you turn your computer speakers down before playing this video):


The noise map comes from this remarkably comprehensive website about traffic noise.