U.S. Secretary of Transportation Ray LaHood told The New York Times Magazine reporter Deborah Solomon, “America is one big pothole” in its June 14, 2009 issue dedicated to the country’s infrastructure. From an historical perspective, he might as well have said America’s military and economic strength is crumbling. Since ancient times, the existence and quality of roads have made and broken empires.
Indeed, the lifeblood of countries is the functioning of roads. Four thousand years ago the earliest legs of the Silk Road linked Asian and Middle Eastern cultures and commerce. The Mongol Hordes traveled that route, and it was essential to the success of the Tang Dynasty. Marco Polo used it to learn about the Far East and bring ideas back home to Venice. Much of the Silk Road was little more than a dirt path worn by beasts of burden, so when floods washed out sections or made them too muddy to traverse, all movement came to a screeching halt (as much as a camel, horse or elephant can screech).
The Romans of course kicked things up a notch. With their affinity for infrastructure – think aqueducts and the Appian Way, built around 312 B.C. to link Rome with Brindisi – and the need to control the parts of three continents, they built roads throughout their empire. Reportedly using methods devised earlier by the Carthagians, they would first plow and remove loose earth to essentially build roads on bedrock flanked by ditches. Their goal – and the goal of all road building to this day – is to channel rain water away from the road such that it doesn’t impede travel or erode the road itself.
Erosion. It’s what leads to the potholes that Secretary LaHood mentions. The more things change, the more they stay the same.
The method the Romans used, as well as all subsequent methods and technologies, is to create a subsurface that supports the weight of traffic, along with a top layer which channels the water away. The highways of the ancient Roman Empire varied according to materials located nearby, but often involved packing gravel on top of bedrock, and “metaling” the top layer with finer stones. Metaling was a slag of gravel and iron waste, which rusted together over time providing a solid, water-repelling surface. In important Roman cities, however, solid rock was used for important streets and roads.
But not every area had bedrock near the surface. They had to make do in certain regions, and that was considered a weakness when the Roman soldiers had to travel quickly to an insubordinate province. Once again, road building and repair had the power to make or break an empire and its economy.
The age of macadam
Modern roads are attributed to Scotsman John McAdam (1756-1836), an engineer and road builder whose “macadamization” improvised upon the Carthagian-Roman Empire method, primarily by using physics to bind the stones together. Something that had held back road building up until this point was the belief that a solid bedrock subsurface was essential to road integrity. Not so, claimed McAdam, who hypothesized that as long as the road crust could stand up to traffic and not be undermined by water, things would work fine.
He was right. Roads could now be built in many more places and at a lower cost. The “macadam” road was adopted and remains the basis for most road building today. Not that it completely eliminated the problems of wear and water (check back to LaHood’s remark).
Initially, he used water to bind the upper layer of rocks, which worked pretty well because only angular rocks were used in the two sublayers of the road (a kinder, less pointy type of rock was used on surface layer in combination with sand and dirt). By compacting the whole shebang with a roller, the angular rocks locked and the top layer bound together as well.
The other key innovation of the macadam road building method was a crowned (peaked) center on the road, which causes rainwater to drain off the road to side ditches.
Then came cars
Things worked pretty well for several decades, until the advent of faster-moving motorized vehicles. These horseless carriages – automobiles – moved at such speeds that they’d suck up the dust in the water-bound surface level. Ultimately this began to pull the road apart as the binder of dust was lost.
Enter the use of tar to accommodate the car. This worked: it held the stones together, eliminated dust and further helped channel water away. The first roads to use this “asphalt” method – compounds of hydrogen and carbon with lesser amounts of nitrogen, sulfur and oxygen – were Fifth Avenue in New York City (1872) and Pennsylvania Avenue in Washington, DC (1877), fronting The White House. Not coincidentally, asphalt production was patented in 1871 by Nathan B. Abbott of Brooklyn, NY. While there is no actual reporting of this, one assumes presidents and New York mayors of the late 19th century were witnesses to the first modern potholes.
Side note: Recorded use of asphalt as a road building material goes back to as early as 625 B.C. in Babylon, as well in baths and water tanks around the same time in Phoenecia, Egypt and the Roman Empire. But it took until the 1800s to become paired with the macadam method. Also, the Great Chicago Fire of 1871 happened because the entire city was then built of wood – including streets and sidewalks. Post-fire, the use of stone materials was written into city codes to prevent a repeat of that catastrophe. Chicago may have its share of potholes today, but at least the streets don’t burn.
Needless to say, Henry Ford’s mass production of the affordable car created demand for more and better roads. World War II drove asphalt technology further to accommodate heavy military vehicles. This was followed by the post-War economic boom, which put a car in virtually every driveway. It was a time when road building involved use of electronic leveling, double-lane pavers (for sped-up road building) and vibrating steel-wheel rollers. The goal in road construction was to reduce noise, improve durability, increase safety by way of skid resistance, reduce splash and spray and create a smoother ride.
The 1956 Federal-Aid Highway Act (a.k.a., the National Interstate and Defense Highways Act) funded the huge cross-country highway program. It modernized the networks connecting population centers across the country. One out of every five miles within the 41,000 mile system is a straight line. Why? To be used as a landing strip for airplanes if need be.
But it wasn’t just about economic growth – military strength was a driver of history’s largest road building effort. The 1956 Federal-Aid Highway Act (a.k.a., the National Interstate and Defense Highways Act) funded the huge cross-country highway program. It modernized the networks connecting population centers across the country. One out of every five miles within the 41,000 mile system is a straight line. Why? To be used as a landing strip for airplanes if need be.
Some of the roads in this system were built of concrete. At the time, it was believed to be superior to asphalt macadam roads. But other features – cost, flexibility, speed of construction, noise and gas fuel economy – favored asphalt over time. Today about 96% of all paved roads and streets in the U.S. (two million miles) are asphalt.
But potholes are still with us
Those highways built in the 1950s are at the end of their expected 50-year lifespan. Certainly, repair work has occurred out of necessity almost before the first generation of roads were completed. Traffic loads have grown over the years, far beyond originally envisioned levels, as both passenger vehicles and commercial trucks have increased with population and economic growth. No domestic wars have put the roads into use for that purpose, but the economic well-being of the country is clearly dependent on our roadways: 80 percent of all goods travel by trucks, which amounts to $25 billion in goods every single day. Over the past two decades, that traffic increased by 50 percent.
Potholes and other road deterioration plague those multilane highways as much as they do millions of miles of avenues, boulevards, streets and alleys. Traditional methods for patching holes work inadequately at best. A 2009 report, “Rough Roads Ahead, Fix Them Now or Pay for It Later” by the American Association of State Highway and Transportation Officials (AASHTO), and TRIP, a national transportation research group, says that all levels of government (local, state and federal) should allocate at least $80 billion per year for the repair and rebuilding of existing roads. Only $27.5 billion has been earmarked for highway repair in the American Reinvestment and Recovery Act of 2009.
Perhaps our best hope is in innovative technology, both for building roads anew and in repair work. Advances in the art are coming in many forms:
- The Washington State Department of Transportation hopes to extend use of existing concrete roads with dowel-bar retrofits, bonded concrete overlays and ultra-thin white topping (two to four inches thick) over existing asphalt for quick road repairs.
- State departments of transportation in Maryland, Michigan, Minnesota, Oregon and Rhode Island use high tech tools to identify deteriorating surfaces and sublayers at an early stage to determine where to target repair work.
- Many cities are testing “pothole killer” vehicles, a truck with robotic arms that enable one driver to fix 100 holes per day, a vast improvement on the 10-15 potholes a traditional four-person crew can patch in a work shift.
- New permanent cold asphalt mixes are more cost-efficient, last longer, store better and apply more efficiently (including in standing water) with the same equipment and very similar techniques currently and commonly used in hot-mix asphalt repair.
- “Perpetual pave” asphalt materials and methods, first introduced in the 1990s, are being refined to last longer than 50 years and with less maintenance overall.
All of this requires an upfront investment, of course, which is all the more challenging at a time when local, state and federal budgets are strapped by a severe economic recession.
Secretary LaHood is undaunted. “Americans are ready for their streets and roads and bridges to be fixed up,” he told The New York Times.