The problem is all the old streets and highways. But thanks to the SHRP program, better fixes are here.
Man first went to the moon 40 years ago, and today Space Shuttle flights are commonplace. Scientists are beginning to grow spare body parts from stem cells, and the computing power packed into our cell phones continues to evolve at a dizzying pace.
So why are there so many problems with roads and highways? Potholes stretch from Honolulu to Chicago to Nashville and Miami, and the problem only seems to get worse. Can’t we figure out how to make better pavement?
Actually, the roads being built today are better than ever. Human nature recalls the bad potholes, ruts, seams and construction tie-ups that punctuate our travels, but when traveling on good, nicely-paved highways and byways – which are either new or older and well-constructed and maintained – we might just remember the scenery or something else.
Going back a bit further, before the federal highway system was authorized and funded by Congress in 1956, roads were far more dangerous. The national fatality rate was 6.05 deaths per 100 million miles traveled. Today on the nation’s interstates it is 0.8 deaths. Factoring in secondary roads, that number goes up to 1.46 deaths per 100 million miles traveled, but this is still a vast improvement. This has come about through not only safer cars, but also technological advances in road design and maintenance that include wider shoulders, better guardrails, “breakaway” signposts and utility poles, improved signs and pavement markings, pavement that is slid-resistant, and clearer sight lines for drivers.
The problem is that every inch of America’s four million miles or highways, roads and streets, and 660,000 bridges, are aging. Most were built in a frenzy of construction after the passage of the Interstate Highway Act during the 1950s, in the post-World War II era when mobilization of the masses was happening on a huge scale. Over the years, more than $129 billion have spent on construction alone, an investment never questioned because of its vital importance to the economy, national defense and the American way of life.
That was a full fifty years ago for the first generation of roads, which presents a very specific problem: Roads are built to last about 50 years. Even under the best conditions, these roads are getting older, even while the population is concurrently growing and increasingly mobile. Old roads plus more traffic equals road deterioration at an accelerating rate.
Clearly, road engineers and the research and development people who came up with safer road features have a Herculean task in front of them where it comes to pavement longevity. How do they make pavement more resilient? How can our roads be made to last longer and be less costly?
Congress got involved – and it worked!
Because of the investment that federal, state and local governments have made in roads – and the absolute dependence of commerce, safety and national security in a functioning highway system – a great deal of resources and study have gone into road building and maintenance.
In other words, the government agencies that build and maintain the roads are just as frustrated as everyone else with pavement deterioration.
In 1987, Congress funded a five-year, $150 million research program that focused on improvement of the nation’s highways in terms of performance, durability, safety and efficiency.
In 1987, Congress funded a five-year, $150 million research program that focused on improvement of the nation’s highways in terms of performance, durability, safety and efficiency. Officially known as the Surface Transportation and Uniform Relocation Act, it established the Strategic Highway Research Program (SHRP, called “sharp”). The program dissects the roads we travel on and what improves the quality of our ride in four essential areas:
Concrete and structures: How best to mix, build, assess, protect and rehabilitate existing concrete roads and bridges.
Asphalt: Identify new approaches to asphalt. Roads made of asphalt are traditionally built with a hot asphalt mix, yet good performance over time was sporadic while maintenance is costly, unwieldy and disruptive.
Highway operations: Improve snow and ice control, find better ways to do preservation work and increase work zone safety.
Pavement performance/The Long Term Pavement Performance Program (LTPP): This ultimately became a 20-year study of 2000 test sections of American and Canadian roads, which identified best practices in building and maintaining pavement.
From the SHRP program, more than 100 new products were identified as furthering pavement performance. A full third of the budget ($53 million) was spent on asphalt research – and for good reason. Asphalt is the predominant building material in roads. It is easier to put down than concrete, and the raw materials – largely aggregates of stone, sand and gravel, and petroleum byproducts – are readily available. About 4000 asphalt mixing plants across the country use the traditional hot mix method, the nature of which forces construction and repair work to be completed within a window of hours, before the mix cools.
What came of the asphalt research in the SHRP program was something called Superpave (Superior Performing Asphalt Pavements). Overall, Superpave is an asphalt mix-design process that accounts for the differences in local conditions found in, for example, Minneapolis versus Miami. It prescribes an ideal asphalt binder, also known as the PG asphalt binder specification, which more accurately addresses conditions where a road is built. This includes factors of climate and use, the latter of which includes how physical properties of the road (such as viscosity) age, how the road deforms (or doesn’t) to form ruts or cracks, and the road’s relatively volatility (flammability).
One researcher who worked on the Superpave program, Mike Anderson, associate director of research at the Asphalt Institute (Lexington, KY), says, “Within volumetric mix design, materials selection and development of aggregate structure are vital. Once these are set, the determination of binder content and moisture-sensitivity just flow from the other conditions.” Key characteristics of Superpave mixes are:
- Clean and angular aggregate
- Controls on the amount of rounded, natural sand in a mix that could lead to instability; the Superpave mix is coarser than conventional mix.
- Binder selection according to local weather data, physical property tests and other guidelines.
- Mix according to a road’s known or anticipated traffic levels, defined in the SHRP program according to three degrees of road use (light, medium and heavy).
Cold mix asphalt has been a Holy Grail of pavement research, in part because its application can reduce many of logistical issues in new construction and, especially, pavement preservation and reactive pothole repair. Traditional hot-mix asphalt can cool in a matter of hours, from plant to roadwork, thus requiring work crews to schedule around the temperature of the mix, not the work itself. Performance of hot mix asphalt in, say, a spot pothole repair is notoriously dismal as well, yielding poor road conditions even after motorists endure traffic delays when road repair crews block lanes.
Improvements like this are never as exciting as a Shuttle launch. Heck – the opening of a new highway is guaranteed to get more press than a road repair that simply doesn’t disintegrate over a few decades.
But when the ride is smoother, when there are fewer repair crew traffic delays, and when long-term maintenance costs come in under budget, the news can’t get better for motorists and taxpayers.
