Monday, 28 February 2011

The Heavy Cost of Road Maintenance

Jersey's roads are not designed to withstand heavy traffic and ice, according to the man looking after the island's infrastructure. Kevin Armstrong, who is responsible for highways at transport and technical services, said ideally all the roads should be resurfaced regularly.. He said Transport and Technical Services responded quickly to potholes in the island but he added that they did not have the resources or enough contractors to respond immediately, so they had to assess the situation on a case-by-case basis. He said: "If it is where there is heavy vehicle use or on a blind bend then we respond quickly but on country roads we would take more time."

Mr Armstrong said he wanted to introduce a 24-hour, 48-hour and a seven-day response system but did not have enough contractors available in Jersey to make it happen. He said: "Ideally the roads would never get to a stage where you have potholes appearing, with the exception of bad weather. "But that would require regular resurfacing of all roads and we don't have the budget or more importantly the contractors to do that."(1)

I wonder what road material is used for surfacing the roads locally. There is an interesting comment from an American journal "Washington Monthly", which compares American roads - and their deterioration - to French roads, and the better materials used in  their composition. Note - the American term "pavement" refers to roads, not pavements, which are "sidewalks" in America:

No one but the French would adorn the industrial strength Autoroute from Nancy to Nice with miles and miles of flowers. Yet a driver can afford to sit back and enjoy the foliage, because he never has to worry about hitting a pothole. Despite a higher percentage of trucks (with heavier payloads than permitted in the U.S.), despite millions of travelers annually, there are virtually no crevices in the Autoroute -or, in fact, in most of France's major roads.

The reason is that France, like the rest of Europe, has over the past few decades made a concerted effort to build roads with an eye to the long haul-to spend early to avoid spending more later. They mix their asphalt with additives-rubber, carbon, polyethylene-to a far greater extent than Americans do. And they make wide use of new technologies like Novophalt, a polymer-modified asphalt binder that gives cement more flexibility and thus increases the pavement's service life. Novophalt, which Europeans began using enthusiastically in 1976, costs between 4 and 8 percent more than traditional asphalt, but it lengthens the pavement's life between 50-100 percent. (2)

The binder Novophalt also is mentioned in a 2008 study in the "Emirates Journal for Engineering Research", (Vol. 13, No.1, 2008), which gives a detailed scientific assessment of traditional asphalt roads which is well worth reading. The authors provide a wealth of detailed, factual, data on the performances of the two road surfaces, and conclude that:

the rate of deterioration of normal asphalt pavement is greatly higher than the corresponding of Novophalt pavement. (3)

On a cost basis, Novophalt is more expensive but it increases the lifespan of the road surface considerably:

This means that the Novophalt pavement initial cost is higher than the normal asphalt pavement by 19%. But, the Novophalt increased the pavement service life by approximately 53% (3)

They conclude that:

From the economic point of view, the Novophalt pavement initial cost is higher than that of the normal asphalt pavement by about 19%. On the other hand, the overall service life cost of Novophalt asphalt less than that of the normal asphalt pavement by 17%. This means that from the economic point of view, using Novophalt pavement is more economical than using asphalt ones. (3)

I wonder what materials are used for Jersey road surfaces, and if they use modern materials such as Novophalt. I haven't been able to find it on any searches of the main government websites. Perhaps a matter for scrutiny?

The other main impact on roads, more than cars, is heavy vehicles. A small pothole can rapidly become a gaping chasm, as it is chipped away with large goods vehicles passing over it. The impact of large vehicles can be considerable. Here is an American comment:

Overweight trucks not only take longer to brake and are more prone to roll over in crashes, but they also damage roads and bridges at rapidly increasing rates even when slightly overloaded..... One legal 80,000 pound GVW tractor-trailer truck does as much damage to road pavement as 9,600 cars. (4)

The Danish study on "Road wear from Heavy Vehicles" from 2008 looks at how larger vehicles impact on road surfaces, and - using both mathematical formula and experimental analysis - notes that using dual tyres can make a significant difference in how the load impacts on the road surface:

Cebon concludes that various experimental and theoretical studies have indicated that single and wide based single tyres can cause up to 10 times more fatigue damage on thin flexible pavements, compared to dual tyres carrying the same static load. (5)

However, the type of tyre itself makes little difference, but the thickness and flexibility of the road surface is more important, as does the tyre pressure:

Moreover, tyre contact conditions are less important for rutting of thicker flexible pavements for which wide single tyres are only 1.5 - 2 times more damaging than dual tyres, and that the tyre type has little influence on fatigue damage of rigid pavements.

Cebon reports that several studies has indicated that fatigue damage due to tensile strain at the bottom a thin asphalt pavements is likely to increase rapidly with average contact pressure, while the inflation pressure has little effect on subgrade rutting. Based on asphalt pavement strain measurements, it has been reported that a 40% increase in tyre pressure would increase fatigue damage by 26%. (5)

We cannot remove heavy vehicles easily from Jersey roads, but it may be useful to ensure that they have the kind of dual tyres and appropriate tyre pressures to cause the minimum of damage to road surfaces.

(2) Why American Roads All Go to Pot. Betsy Dance, Washington Monthly, 1991

1 comment:

Anonymous said...

Ponder also the beneficial effect of air suspension on the road surface - there are many elderly sub-P30 commercials on the roads, principally skip wagons and scaffolding lorries. These may be of such a vintage that old-style leaf springs are still commonplace, and the rebound effects can be considerable.