What maketh a road?
In parts they are as wide as a football pitch and they cover the country in a seemingly endless network, but ask most how they are made and you’re greeted with blank stares. Like most areas, knowing more about roads, their variety and their composition can help you as a driver to manage your own experience on the roads. This is especially true when it comes to smaller and unsealed country roads. This week we looked at all things bitumen to understand a little more about the many veins and arteries that serve our sprawling cities towns and settlements.
Some of the facts
The standard lane width is 3.5m, however elements like vehicle type/volume, speed and lane type can impact lane size. Additionally, lane size can vary with some as small as thin as 2.3m (Collins St. Melbourne). The main types of road in Australia are below;
1. Freeways / motorways / expressways and tollways – These are roads with consistently more than one lane of traffic in each direction and with a constant median strip. Some have toll booths and in these cases they are called tollways or motorways. Expressway is a largely defunct term in Australia but is used in the names of some older roads.
2. Highways – these are more inconsistent than freeways or any of the roads in point number 1. In essence the number of lanes can change from any number to just one in either direction. Some are not sealed and can be restricted due to weather. Their use can be limited to specific times of year.
3. Minor roads – These are local government managed roads and make up most shorter local rural, outback and urban/town/suburban roads.
a. Outback Roads – these are a special set of minor roads which deserve special mention as they require a high level of local knowledge. They are generally unsealed and can be dangerous and heavily dependent on weather conditions.
How it’s made
The main composition of sealed Australian roads it bitumen, however this is only part of the story. Bitumen is predominantly the surface layer but most sealed roads will have a minimum of 2 other layers which stabilise the roadway. The other 2 layers are primarily made of a mix of bitumen, crushed rock, compacted sand, chalk and larger rocks. Starting from the bottom each layer is rolled and compacted as the road rises from its base. In many cases the materials involved will depend on the local conditions and in many cases more than 3 layers will be needed. More rural roads are usually made of earth, loam, gravel or bituminous spray seal.
A major motorway will have the following layers;
TOP Deep strength asphalt, with thick asphalt on cement stabilised granular sub base
Flexible composite, comprising a thick asphalt on lean concrete sub base
Full depth asphalt
Unbound granular with sprayed seal surfacing
Jointed plain (unreinforced) concrete pavements
Jointed reinforced concrete pavements
BOTTOM Continuously reinforced concrete pavements.
Some fun facts on roads in Australia;
There is more than 817,000 km of road in Australia, less than half of this road is sealed
Australia has around 355,000 km of sealed roads, 257,000km of gravel or improved surface roads and 205,000km of dirt roads
More than $15 billion is spent by government on roads each year
New roads have a design life of 30 years, while a new bridge has a design life of 100 years
It’s easy to forget the masterpiece that is the Australian road network. In spots it’s patchy, unsealed and sometimes curiously unfit for purpose. While most will agree that it has its problems, it has to be pointed out that it is one of the largest and best maintained road networks on the planet. When you consider that it Australia does actually have an extremely sparse population you realise how much effort must go into managing the network.
What do you think of our road network?
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Did you ever think a road could have so many layers?
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