By Jonny Lupsha, Current Events Editor
In the 1950s, the construction of highways often tore the middle of cities. Efforts to accelerate travel between urban and suburban areas in the United States have been extensive and swift. Now some cities are removing the ruined roads.
Roads have been part of civilization for millennia. Those that received more traffic became wider and larger than their less used counterparts, leading to complex networks of major highways, mid-sized roads, and residential streets. Many of these networks in the United States were built in the 1950s and are falling apart.
Roads have always needed repairs, but in the 21st century change is sweeping the country. About 30 cities across the United States are in the process of removing or considering removing some of the more inconvenient highways that cross them. Rochester, New York, for example, has replaced much of its inner loop with a narrower road and housing. Detroit, New Orleans, Dallas and others are considering doing the same.
While the United States is considering taking a few steps back on its highway system, it’s worth considering what goes into road design in the first place. Dr Steven Ressler, professor emeritus at the United States Military Academy at West Point, said highways rely on time-tested systems that balance speed, safety and comfort.
Function at junction
Dr Ressler said roads are classified based on their location, which is urban or rural, and their function, which is either arterial, collector or local.
“The function of an artery is to provide long-distance mobility, making it easier to travel from one region or city to another,” he said. “At the opposite end of the spectrum, local roads provide access into residential areas, commercial districts, and so on. In between, collectors are designed to route traffic between local roads and arteries. “
From the start, designing a pavement is not an easy task. The specific path a road takes along the ground is called its alignment, and Dr Ressler said alignment is affected by a number of factors. Topography and soil conditions, length of route, need to cross or avoid population centers or rivers, need to cross existing railways or other roads, cost of construction , environmental impact, etc. And alignment is just the first step for engineers.
“Next, we’ll define the cross-section configuration, which includes factors such as widths and slopes of traffic lanes, shoulders and embankments,” said Dr Ressler. “Next, we’ll design the pavement, to include the top surface of the asphalt or concrete and the underlying layers of compacted fill.
“We will work with our fellow structural engineers to design any necessary bridges and interchanges, and with our fellow water resources engineers to design the drainage system.”
Finally, he said, engineers plan signage and fencing to control traffic and improve safety.
Of course, different vehicles vary widely in size and function, from compact cars to semi-trailers. Therefore, even facing a simple hill can present safety concerns if the slopes of the road are not carefully considered to accommodate heavy trucks and the changing weight of their cargo. Engineers regularly consult the established safety instructions so as not to exceed the recommended slopes on the roadways.
Once the road engineers have lined up all the stars, they can start building a highway.
Edited by Angela Shoemaker, The Great Courses Daily