Monday, 25 April 2011

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.


Slow Factory said...

I agree with all the methodologies described. Regarding "other countries", here in Berlin on many 30km/h streets the road is rougher than the pavement (sidewalk), so many cyclists illegally use the latter! (Also the speed bumps make cyclists ride into the door zone on cars on a few streets, such as the recommended cycle route through my neighborhood). Some parts of the city are better and what I describe are not the newest implementations.

Is that automatic paving stone device a new thing?

Anonymous said...

The paving machine isn't actually automatic, the bricks are still laid by workers. The difference is that their working position is much more ergonomic as they're sitting in an upright position on top of the machine instead of hunched over the road surface.

It is indeed quite a new innovation, made mandatory about a year ago by new working condition rules. Any road surfacing will have to be done using mechanised means unless provably infeasible.

Mark W. said...

The 'cobbles' are very traditional for Dutch roads. The Dutch simply call them straatstenen which translates to 'street stones' or 'street bricks'. The bricks of backed clay are indeed remarkably smooth to ride on. Especially the newer ones.
There is a whole industry in the Netherlands. With all the rivers clay can be found in abundance so this type of road surface is claimed to be nature friendly.
There is even a foundation to promote the (renewed) use of this traditional material.
As David writes, many streets in 30kph zones are now in cobbles. Asphalt is kept for the through roads. This way the road surface is also an indication as to what type of road you are using.
(The website of the Foundation for the promotion of street bricks is in Dutch only.)

Slow Factory said...

Curious about this solar bike path concept in NL. (By the way in the first comment someone asks "why do bicycle paths need to be high embodied-energy concrete when compacted limestone dust over earth is perfectly fine?" - which makes a good point about concrete and my guess is that limestone etc. is not suitable for high traffic + lots of rain and also perhaps that any snow removal might require re-application of the limestone... and also is there lots of limestone in NL?...)

Also, to add my earlier comment, I would guess that today's super noise and vibration-insulated vehicles would make drivers somewhat immune to what's outside.

David Hembrow said...

GIF: The Fietsberaad have slightly more rational coverage of that idea for cycle paths.

I have to say that I can't see that much point in it. After all, they'll probably work better put on roofs, which are already at a better angle vs. the sun and won't be damaged so quickly or in the shade so often.

But the comment about limestone dust is absurd. It's not "perfectly fine" at all. It's horrible in winter, gets wet and sticky and changes shape. It gets all over your bike too.

Remember that we're talking about replacing road infrastructure with cycle paths. Replacing car journeys with cycle journeys. This means using less of any given surface. If cycle paths are surfaced to make cycling work better than motoring, then this is a part of working towards a lower impact overall.

I do share some concerns about concrete, but I will also say that well made concrete cycle paths are incredibly good to cycle on.

Unknown said...

Unreal. Road management is so poor in the United States that even patching asphalt potholes isn't prioritized. Our municipalities have worked hard to systematically remove Belgian block from historic urban areas, while the Dutch are actively maintaining and installing setts. To an American, this is inconceivable.

Unknown said...

I think they do intentionally lay rougher surfaces for cars coming off smoother car lanes when they enter a road which includes cyclists as an audible signal for car drivers to pay more attention.