How and why are roads built?
Roads get us from A to B, we all know that – but how and why are they built?
Firstly, some history: the first roads were built around 4,000 BC, and they were created with stone and timber. Then, a few thousand years later, the Romans popularised constructing roads using stone paving, mostly in North Africa and Europe, although there is evidence of similar methods being carried out in South America and India.
Road construction has continually improved over the years, by changing stone thickness and slope gradients, stones were eventually laid out in a regular, compact design, covered by smaller stones to produce a solid layer, leading to smoother, stronger roads.
How are roads built?
Nowadays, roads are usually constructed using asphalt and/or concrete.
The construction of modern roads tends to have three distinct processes: setting out, earthworks and paving construction.
Sometimes known as staking out or laying out, setting out is the practice of transferring the building design onto the land itself so that the workers can follow it during construction.
Key points and guide markers are set out to ensure accurate construction takes place. In road building, the setting out procedure usually used is called the profile board method.
A series of boards that show the exact level one metre above the completed construction level are placed at intervals along the proposed line of the road. This ensures the road remains within its limits and identifies what, if any, excavation is needed.
This work is usually carried out by a land surveyor.
Earthwork is where the construction itself really begins – think of it as establishing a stable foundation for the road. It involves the removal of topsoil, as well as any vegetation, before grading and scraping the area to the finished formation level – this is usually done with a bulldozer, grader or tractor shovel.
Typically, it has 5 stages:
- First, the contractor builds embankments using cuts and fills
- Next, a grader or bulldozer levels the screened dirt. Levelling bumps and filling in dips creates a surface that will support a road for decades
- The screened dirt is sprayed with water and compacted to its maximum density
- During this stage, drains and sewers are installed. The centre of the road must be higher than the edges so water will run off into the drains. Drainage is a critical element because improper drainage will greatly reduce the new pavement's life expectancy
- Finally, gravel is placed in layers on the road bed. Workers moisten and compact each layer. Layers are added and compacted until the road bed reaches the height called for in the setting out stage.
Now there’s a solid foundation in place, the final part of building a road is paving. As previously mentioned, roads in the UK tend to be constructed with either asphalt or concrete, sometimes both. Factors such as the costs involved and the amount of expected traffic determine which is used.
Asphalt uses an oil-based substance called bitumen to make sand and crushed rock stick together like glue. Once the asphalt is heated to around 150°C, it’s moved to the construction site. Then, workers spread and compact it onto the foundation.
Concrete also uses sand and crushed rock, but instead uses cement to hold it all together. Liquid concrete is poured into steel moulds called forms, and as it dries, a finishing machine vibrates it to ensure it settles evenly. To prevent cracks, cuts – called joints – are made between concrete slabs. This allows the slabs to contract and expand with changes in temperature without breaking.
Occasionally, an additional layer of asphalt is applied to create extra strength within the road and prevent cracks.
That’s it! Some extra checks are carried out to ensure the road is strong enough to withstand the expected levels of traffic over the coming decades, and once passed, cars can begin driving over it.
Why build a new road?
First, the need has to be there. Local authorities and planning officers will study traffic flows and new/expected building developments to decide when a new road is needed to accommodate these. Usually, there’s four key areas of consideration when planning a new road:
- Reduce traffic and lower journey times
- Improve connections
- Lower noise and air pollution in urban areas
- Reduce collisions.
New roads are long-term investments that are built to stand the test of time and link communities together. From large-scale motorways and dual carriageways to country roads, they are an integral part of supporting daily life.
As well as providing thousands of construction jobs, roads have a very real impact on the wider economy. Improving the speed of moving people and goods from A to B leads to increased levels of productivity – meaning, over time, a well-planned road which meets a real need pays for itself multiple times over.
Now we’ve explored the how and why, let’s take a look at who’s involved in constructing roads.
Jobs involved in road construction
Hundreds of professionals in all sorts of roles, from cost consultants to designers, highways maintenance technicians to legal advisors and more are involved in building a road. We’ve picked a few professions to look at more closely.
Archaeologists increase our understanding of the human past by uncovering and protecting remains and artefacts. These are often uncovered on construction sites and archaeologists ensure they are preserved and can be added to the Historic Environment Records. As an archaeologist, you’d be involved during project planning.
Ecologists study the relationship between plants, animals and the environment. They look at how animals and plants inhabit a particular environment, and report on the likely impact of any proposed roadworks.
Transport modellers use specialist computer software to design and develop transport routes. As a transport modeller, you could design how new road installations link to existing transport systems. You could be designing one-way systems or diversions, while other roads are being repaired, or planning transport systems ahead of large events, such as festivals or protests.
Machine drivers have use bulldozers, 360 excavators and dumper trucks to clear and level land, and to transport heavy materials to and from site. They can transform a landscape in a very short time and have been integral to this large-scale construction project.
That's a small spotlight on some of the professions involved in creating a road - why not take our career explorer to see whether one of these, or the hundreds of other career paths available in construction is right for you?