By Jonny Lupsha, Wondrium Staff Writer
In the 1950s, highway construction often ripped through the middle of cities. Efforts to speed commutes between the urban and suburban areas of the United States were extensive and swift. Now, some cities are removing the crumbling roads.
Roadways have been a part of civilization for millennia. Those that received more traffic became wider and more prominent than their lesser-used counterparts, leading to intricate webs of major highways, mid-sized roads, and residential streets. Many of these networks in the United States were built in the 1950s and are now falling apart.
Roads have always needed repair, but in the 21st century, change is sweeping the nation. Approximately 30 cities across the United States are removing or considering removing some of the more obtrusive highways that run through them. Rochester, New York, for example, replaced much of its Inner Loop with a narrower road and housing. Detroit, New Orleans, Dallas, and others are thinking of following suit.
While America considers backpedaling a couple steps on its highway system, it’s worth looking at what goes into designing roadways in the first place. Dr. Steven Ressler, Professor Emeritus from the United States Military Academy at West Point, said highways rely on time-tested systems that balance speed, safety, and comfort.
Function at the Junction
Dr. Ressler said that roads are classified by their location, which is either urban or rural, and by their function, which is either arterial, collector, or local.
“The function of an arterial is to provide long-distance mobility, facilitating movement from one region or city to another,” he said. “At the opposite end of the spectrum, local roads provide access within residential areas, commercial districts, and so forth. In between, collectors are designed to convey traffic between the local roads and the arterials.”
Right from the outset, designing a roadway is no easy task. The specific path that a roadway takes along the ground is called its alignment, and Dr. Ressler said that alignment is affected by any number of factors. Topography and soil conditions, the length of the route, the need to cross or avoid population centers or rivers, the need to cross railroads or other existing roads, construction cost, environmental impact, and more can influence horizontal and vertical alignment. And alignment is just the first step for engineers.
“Next, we’ll define the cross-section configuration, which includes such factors as the widths and slopes of the traffic lanes, shoulders, and embankments,” Dr. Ressler said. “Then we’ll design the pavement, to include the upper surface of asphalt or concrete and the underlying layers of compacted fill.
“We’ll collaborate with our structural engineering colleagues to design any required bridges and interchanges, and with our water resources engineering colleagues to design the drainage system.”
Finally, he said, engineers plan signage and fencing to control traffic flow and enhance safety.
Of course, different vehicles vary greatly in size and purpose, from compact cars to semi trucks. Therefore, even dealing with a simple hill can present safety problems if road gradients aren’t carefully considered to accommodate heavy trucks and the shifting weight of their cargo. Engineers regularly consult established safety guidelines so as not to exceed recommended slopes on roadways.
Once highway engineers make all the stars align, they can begin work on actually constructing a highway.