Driving on asphalt roads takes less energy
Bitumen is a core component of the asphalt used in road construction and influences the energy that needs to be expended by a vehicle travelling along that road.
The energy efficiency of an asphalt road in use is determined by a combination of many different factors, including rolling resistance, skid resistance and road condition. The inter-relationships between these are extremely complex and further research needs to be conducted in order to fully understand how the different factors affect each another.
Energy efficiency and road maintenance
However, it is clear that the road condition, which is highly influenced by the effectiveness of that road’s preventative maintenance programme, is particularly important to energy efficiency - as well as to safety and to the economy.
Road condition affects energy efficiency because smooth, well-maintained roads:
- Facilitate smoother, more energy-efficient driving: drivers do not need to keep slowing down and then accelerating each time they approach and then pass beyond dangerous and potentially damaging potholes
- Have a longer service life: as suitably funded preventative maintenance programmes not only ensure that the road condition doesn’t prematurely deteriorate, to the extent that the only suitable remedial action is to close the road completely and replace it, but also can actually extend the life of the road
- Do not cause damage to vehicle tyres and suspensions: and so do not lead to the energy-intensive production of additional parts that are damaged when driving on roads in poor condition.
Investment in road maintenance
Clearly, the level of funding provided for road maintenance is crucial and ideally this investment should be sufficient to fund a comprehensive programme of preventative maintenance across the whole road network.
To help road engineers prioritise what preventative maintenance activities should be conducted on which roads, and when, an asset management approach should be adopted to road network management. This approach also helps those responsible for roads make well-informed decisions regarding how to make best use of the finite funds at their disposal.
Energy efficiency and rolling resistance
The lower the rolling resistance of a road pavement, the more energy efficient it is for vehicles. However, a low rolling resistance typically means that friction between the road surface and a vehicle’s tyres is low, which can compromise grip and therefore skid resistance, especially in wet conditions.
Another factor that impacts rolling resistance is the Mean Profile Depth (MPD) of a road, which is a measure of the evenness of the road surface across a section. There are a number of research programmes which are exploring the relationship between a road pavement’s MPD and its rolling resistance, and one of these is the EU-funded MIRIAM project.
Energy efficiency and skid resistance
To have good skid resistance in the wet, a certain MPD is needed. But, as MPD goes up, rolling resistance generally increases and it takes more energy to drive on the road.
Smooth road surfaces typically generate less noise when vehicles drive on them, which is also important – particularly as in certain countries road noise is an environmental consideration included within the technical specification for certain types of roads. In general terms, road users prefer very smooth road surfaces because they are easier and more comfortable to drive upon, compared to highly textured, ‘bumpy’ roads.
Energy efficiency and innovation
The bitumen and asphalt industries continue to invest significant time and money on research and into the development of new materials and mixes that possess certain properties and display particular performance characteristics.
One particularly interesting example is the COOEE project in Denmark, which succeeded in developing a special road surface material which has high skid resistance in the wet, low noise AND a low rolling resistance that in tests reduced average fuel consumption by 4%.
The subject of the ‘Low rolling resistance pavements in Denmark’ technical paper (see abstract on page 225) submitted for the 6th Eurasphalt & Eurobitume Congress in Prague, and also of the ‘CO2 reduction with Low Rolling Resistance Stone Mastic Asphalt‘ presentation at the same Congress, the COOEE mix not only delivers a range of socio-economic benefits, but also offers extremely valuable environmental and financial benefits.
Asphalt roads: more than just energy efficient
As well as being energy efficient for vehicles driving on them, asphalt roads have many other sustainability benefits and these are summarized on the Sustainability page of the Asphalt Advantages website.