The Road Taken, by Henry Petroski, is a jaunty tour of America's transportation infrastructure. It tells the story of how our highways and rails came to be, why certain decisions were made, and what problems must now be addressed. The book is part history lesson and part call for action. Our roads and bridges are aging, costing billions of dollars in productivity, to say nothing of lives lost. As Petroski explains, "Reflecting on some of the seemingly less consequential choices that have been made—whether stop signs should be red or yellow, whether the red or green light should be topmost in a traffic signal, whether a suburban street should be called a drive or a road—can help us think through larger choices." Here are eight things you might not know about the history of American transportation.

1. A DRIVE TO UTOPIA GAVE US GREEN INTERSTATE HIGHWAY SIGNS.

To decide on the color of interstate highway signs, variously colored signs were erected along a stretch of roadway in the mid-1950s. The signs led to two cities: Utopia and Metropolis. Drivers were later polled about which sign color they preferred. Green came out on top at 58 percent, followed by blue (27 percent), and black (15 percent).

The chosen typeface for highway signs (Highway Gothic) would later be reconsidered by highway officials. The driving population was aging fast, and vision problems were a concern. Officials considered using a larger type, but that meant larger signs. In the late 1980s, a new typeface was designed to address the problem. Called Clearview, it increased visibility of sign wordage by 50 percent. Finally, in 2004, the highway administration gave it interim approval. ("Infrastructural things can move slowly and indecisively even where interstate highways are concerned," writes Petroski.) In 2009, officials failed to endorse Clearview because it was still in testing. (Numbers had yet to be evaluated.) Earlier this year, the government abandoned the whole effort.

2. SPILLED MILK GAVE US CENTER LINES ON THE ROAD.

"As late as 1917," writes Petroski, "pavements on rural highways were unadorned with lines or stripes of any kind." It was just understood that drivers were to hug the right side of the road. This understanding, however, fell apart on curves, where drivers tended to veer into the opposite lane. It was decided that lines were needed. The first modern centerline was painted in 1917. White was chosen by its designer, Edward Hines, who was inspired after seeing milk spill from a delivery wagon on a newly-paved road.

In 1935, highway officials gave local governments options when it came to painting centerlines. They could be either yellow, white, or black, depending on the color of the underlying pavement. By 1955, 49 states had adopted white. The lonely holdout, Oregon, preferred yellow, arguing that it was safer. The federal government balked at such a ridiculous suggestion and threatened to withhold $300 million in highway funds. Oregon complied, but must surely have felt a smug sense of satisfaction in 1971, when the federal government mandated that centerlines now be painted yellow, with white stripes reserved for roads where traffic drove in the same direction. (Lines on the sides of roads didn't gain traction with officials until the mid-1950s. Before that, edge markings were prohibited. They were finally advocated in 1961, and then mandated in 1978.)

3. STOP SIGNS ARE DIAMONDS WITH THE POINTS CHOPPED OFF.

Stop signs were a hot-button issue in the 1920s. Originally called "boulevard stops," they were black and diamond-shaped. Boulevard stops applied to roads that crossed major urban throughways. The problem, according to people who lived on these "boulevard stop streets," was that cars on roads with the right-of-way drove faster, and thus more dangerously. Stop signs had become a public menace! The Illinois courts even ruled them illegal—"a violation of the right of individuals to cross the street."

The signs got their familiar octagonal shape when a Detroit police sergeant cut the corners from the diamond to distinguish stop signs from other caution signs (all of which were diamond shaped at the time). The idea of using a red sign with white lettering first appeared in 1924, though the American Association of State Highway Officials rejected that color in favor of yellow octagons. (Red faded, making them difficult to see at night.) It wasn't until the creation of fade-resistant finishes that red really gained traction. In 1954, regulators mandated that stop signs be painted red with white lettering.

4. STOP LIGHTS WERE INVENTED BY COPS WHO WERE TIRED OF ALMOST BEING RUN OVER.

Before there were traffic lights, police officers had to direct traffic by hand, which could be a dangerous job. The public was new to driving, after all. Various systems to automate and solve the problem were patented, including a system using movable arms similar to those used by the railroad. According to the American Association of State Highway and Transportation Officials, it was a traffic cop who had the idea of using lights instead of hand signals or flags.

"Officer Lester F. Wire didn't feel safe when he was directing cars, trucks, buggies, and trolleys at a busy intersection in downtown Salt Lake City in 1912," writes Petroski. "So he built a birdhouse made of plywood, painted it yellow, and punched six-inch holes on either side. He then dipped bulbs in red and green paint and used a manual switch to change the lights from red to green. By 1917, Salt Lake City had traffic signals at six connected intersections, all controlled simultaneously from one manual switch. It was the first interconnected traffic signal system in the United States."

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5. THE YELLOW LIGHT SOLVED A JARRING PROBLEM.

Green and red traffic lights had one pretty obvious problem: drivers had to stop and go on a dime, with no warning. According to Petroski, before a yellow light was added to the mix, switches were devised for "the green light to remain illuminated for a few seconds after the red came on so that oncoming drivers were given warning that the light was changing." The first yellow light was added in 1917 by Detroit police officer William Potts.

6. THE FIRST NEW YORK CITY SUBWAY WAS ILLEGAL.

The first subway in New York City was built illegally by Alfred E. Beach, then-editor of Scientific American. Traffic on New York roadways was a pressing concern for the city, and an underground train system was a tempting option. Beach came up with the idea of installing a subterranean, pneumatic tube system in which a train car was pushed by powerful fans. It was a political nonstarter, however. Proponents of elevated trains had political clout, and there were fears that underground trains would have pollution consequences. To get the necessary construction permits, Beach sold the New York state legislature on a different plan. "Under the ruse of installing a system of message- and small-parcel-carrying pneumatic tubes beneath Broadway, he surreptitiously had a prototype of his subway constructed." Upon completion in 1870, "Beach unveiled his fait accompli to the public, who paid to travel in it as if it were an amusement ride."

7. JERSEY BARRIERS ARE NOT FROM NEW JERSEY.

The concrete dividers between opposing lanes of traffic in metropolitan areas are called Jersey barriers. They were first used in the 1940s on a dangerous stretch of U.S. Route 99 south of Bakersfield, California. "Using the durable dividers in place of guardrails or other, more transparent barriers against car and truck crossover appears to have been motivated at least in part by a desire to reduce the need for highway crews to make repairs in that dangerous location." The barriers have changed in shape and design over the years, a result of changing vehicle styles and grim data from real world collisions. (The barriers didn't reach New Jersey until 1955.)

8. POTHOLES ARE A REDUNDANCY.

The word "pothole" preceded the automobile. It is a combination of pot, which is a Middle English word meaning "pit," and, well, hole. "Pothole" thus means "holehole." They are the result of water seeping into the ground and somehow winding up beneath a roadway. When seasons change, the water expands as it freezes, stretching the road's surface. Small cracks develop, which collect water, which freezes, which expands the cracks, and so on. Add cars driving endlessly over the structure, and you get serious crumbling and fatigue. When the ice or water melts or evaporates, the asphalt collapses into the space. Cars, little by little, chip and carry away the asphalt while simultaneously pushing the hole deeper. Eventually, the ubiquitous irritant to everyone's morning commute is developed, making our road taken a bumpy one indeed.