# Why do we pave roads instead of making them from removable parts?

If roads were made of removable parts, we'd probably have fiber cable internet everywhere by now I'd say.
It'd be so much easier to install e.g. new electricity and water infrastructure and to maintain them if roads where made like that. We'd be able to redefine the whole architecture of a neighborhood if necessary, without the need to take existing roads into account. We could even make an urban area a landscape again with ease if e.g. a city wanted more green areas somewhere. We could make machines that piled road parts on top of each other making maintenance as easy as pie. So why do we still pave roads? There's probably some aspect of civil engineering I'm not taking into account..

• people would definitely steal roads though.... – Yuri Borges Jun 6 '15 at 14:31
• I think it has more to do with cost and civil engineering history – 706Astor Jun 6 '15 at 14:46
• Brick roadways only work for pedestrian, cyclist and equestrian traffic. They're hell to maintain for vehicle traffic, even with very low speed limits. community.seattletimes.nwsource.com/archive/… – Air Jun 6 '15 at 17:18
• the Dutch seem to like it a lot for low speed traffic too. I can imagine that brick roads are difficult to maintain. The pieces are just too small. Putting them on top of a plate of some other material should make it a bit easier to manage them – Yuri Borges Jun 6 '15 at 17:29
• Building replaceable parts that are durable enough to actually be used for roads, is much more expensive than just paving, and breaking it up if you need to dig something. Manpower to dig up, and then re-pave, a road, really isn't that hard, compared to the significant engineering and manufacturing cost in trying to build durable and re-usable parts out of, I don't know, steel, or aluminum, or something. – Jon Watte Jun 7 '15 at 2:52

This is very common misunderstanding. When we look a a road, we see few centimeters thick layer of bituminous surface, and we think about "the road" as "the asphalt/tarmac."

It's not.

When you look how a road is build (or rebuilt), you can see that "the road" is actually over half a meter (or more) deep, consists of layers of sand and gravel and has complex rainwater draining system. And this is the most expensive part of the road: the soft, movable and adaptable interface which connects hard surface to soft soil.

Even "removable" roads, made of cobblestone or concrete panels require exactly same understructure. Even "trivial" sidewalks require identical understructure (on a smaller scale). If you ever see amateur-made sidewalks, created by simply laying flat stones or concrete panels on the ground, pay close attention to how individual panels fit the ground. When new, they're fine. But after few years, with usage and water flushing some ground away, they become notoriously unstable. Temporary walkways set up on concerts or other mass events often exhibit same problems within a day (as they're used quite heavily).

Optimizing costs of reassembling surface is optimizing the least expensive part of a road.

There are also other reasons, e.g. paving is mechanized process and very efficient, joints suck and make very bad driving and walking experience, road is a structure tightly tailored to local needs (width, curve radii, bank, elevation) and it's not possible to make a prefabricated road that would cover every possible application. Perhaps the last problem is what completely obliterates your proposed benefits: instead of saying "let's have a road here" we'll be more like:

• Is it possible to lay our road around here?
• Nope, we don't have this radius.
• Maybe between those buildings there?
• Sorry, it's 5 cm too wide, it won't fit without violating building code.
• Up that hill?
• We'll have to either flatten this hill to 0.001% or make it more steep to 0.002%, because roads come only in those elevations.

You mean going back to cobblestone roads? Many sidewalks are often paved with pavers.

One of the challenges is maintaining a level surface. Asphalt holds itself together like a sheet and a dip in the surface below will pull on the sides delaying the onset of potholes. while separate parts will start moving under the vibration and frost heaving.

Once the surface is uneven cars going over them will be loud. In this street there is a busline going through and each time the bus runs through those living there know it by the noise and vibration.

Laying pavers is a very labour-intensive work, each stone must be layed and put into place individually. Before you can even start doing that you need to flatten and compact the surface below.

However lets go in between small pavers and a single sheet of asphalt: concrete slabs. This road is a good example. However replacing those isn't as easy as you think it is. You need to close down the entire lane break up the old slab using a jack hammer clean up the debris and crane in the new slab. Then they need to fill the joint.

I think that there are a few things that you aren't considering.

Most roads have at least 12 in (300 mm) of compacted aggregate (rock) under the actual pavement. If the existing soil is very weak, then this depth of aggregate subbase can be increased. Sometimes the soil needs to be strengthened by mixing in cement.

This means that just removing road panels doesn't completely remove the road structure.

### Pavement Joints

If you have ever driven over a concrete road that has joints, you will notice that the ride is rougher and the road noise is louder. Each time a vehicle travels over a joint in the road, there is a bump. To help minimize this, a layer of asphalt is sometimes placed over the concrete. This creates a smoother ride by creating a flatter surface. This is another strike against pavement panels.

### Frequency of change

Part of the proposal seems to be based on the thought that roads will be replaced or moved frequently. No matter how easy it is to change the land use from road to green space, it will be wasteful to spend time doing so. I don't know of any area where this type of change would happen often enough to justify the work required. Land use is planned in advance for a reason. There are also already ways to make temporary roads for special circumstances.

As some of the other posters have mentioned a road has several built up layers (hopefully). The drainage system is usually very important. Bad quality roads are usually because the drainage is poor or non-existent. Roman roads were sometimes as much as 10 feet thick, which is why many are still in use today, 2000 years later.

It is possible to create a temporary road using steel. Using steel mesh and bar you can create a road that will just lay on dirt. It is EXTREMELY expensive, but in the future if metal become cheaper than rock, metal roads could become a reality. Currently, they are only used in specialized military situations.

Other answers have well described a road is a lot more than just the surface layer and the vast majority of the cost is the planning and logistics involved rather than the actual materials.

Current road building materials are generally pretty much as cheap as engineering materials get, indeed many are effectively waste products from other industries.

Also consider asphalt/tarmac. It is hard to think of a material better suited to its purpose.

• It provides excellent grip in both wet and dry conditions for rubber tyres and maintains this pretty much regardless of wear.
• It is cheap
• Easy to lay, you basically just dump it out of the back of a truck, grade it and compact it. Once you have the sub grades a tarmac laying machine can put down a road surface at a moderate walking pace.
• It's easy to make local repairs and if done properly they will blend seamlessly with the existing surface.
• The basic repair kit is tar and stone chips, you can even get premixed bags of the stuff that you can just dump in a hole.
• It can be renovated by planing the surface and relaying the top layer. For minor roads you can just spray them with tar and spread stone chips over the top.
• You can accommodate any arbitrary carriageway width, curve or camber.
• It is very abrasion resistant and can self repair to some extent.
• Bitumen, the binding agent is a byproduct of crude oil refining, it doesn't really have any other use so in environmental terms it is essentially free as long as there is any market for other crude oil products. It is also highly recyclable.
• Aside from earthquakes or bombs asphalt roads can't really fail catastrophically

Pavers or some similar pavement is very labor intensive. While a person places each brick a machine will place the vast majority of asphalt (HMA) or concrete (PCC). While there are machines that can place large quantities of brick at once they are not widely in use (That I've seen anyway).

Paver roads are also very maintenance intensive. If not well maintained then something normal like snowplowing over a road with pieces can be difficult or dangerous as an individual brick can catch the plow and be "shot" out away from the plow. The driver has to be careful and the road has to be kept in good shape. Overall this makes PCC or HMA roads more cost effective. Roads really are pieced together anyway. They're just blended/layered in a way that makes it harder to notice. In most concrete roads (once the bad part is broken out) dowel rods are inserted into adjacent sections of concrete thereby preventing too much vertical shift but still allowing for the pieces to remain separate. As to movement of roads. Generally roads are built on Right of Way (ROW). ROW is property that is for the common good. This is where all the utilities run (or in an easement) and the roads. The reason you can't just move a road is because it's in the ROW which is property set apart from a private parcel nearby. Meaning you don't generally own to the middle of the street. You own some feet back from the street and the City "owns" the rest. That makes it slightly more difficult to rearrange roads etc. Not to mention the cost of relocating the utilities. A previous project I did cost almost $500k to take power lines and put them underground for a 1/2 mile. Those power lines did not change their location except for elevation. • Hi Dano0430, welcome to Engineering Stack Exchange! Your answer makes some good points but could stand some revision. We strongly encourage reference-quality writing. Well-formatted paragraphs and credible citations go a long way to turn a decent answer into a great one that attracts many upvotes over time. – Air Jun 9 '15 at 17:02 Something that was touched on but not fully addressed is the cost of building roads as they are today. I believe the cost of building a new road is about$1 million per mile, which seems like a great deal of money until you really think about all the planning and work put into a road. One million USD per mile is incredibly efficient, so it would have to take something cheaper than that to contend with the current system.

• Be careful when you used "One million dollars per mile". It might be an order of magnitude estimate, but I have heard very different things all estimated the same way. – hazzey Jun 9 '15 at 2:09