The next time you're in a parking lot, or when you're walking on the sidewalk along a street with lots of parked cars, take a look at the windshield wipers. On some cars, the wiper arms are mounted fairly close to each other and are designed to move in unison. On others, the arms are mounted at opposite sides of the car and face each other in the center of the windshield. Some wiper arms are short and some are long. Some are straight, and some, especially on newer cars, are curved or bent.

Like so many things we take for granted, wiper design turns out to be a surprisingly nuanced rabbit hole once you take a moment to notice it, with no two cars seeming to have the same configuration. It's fun to imagine an army of industrious wiper elves coming up with just the right design to provide the proper visual accent for each vehicle.

But the reality is that wiper design is driven primarily by practicalities, not aesthetics. "The wiper system is usually designed pretty late in the process," said Doug Patton, executive vice president of engineering for Denso International America, which makes wiper systems and other automotive components for many car brands. "That's why you see these variations from car to car. The wiper system is usually designed to work within the rest of the vehicle design."

The most common wiper configuration is what's called a tandem system, with the two wipers moving back and forth in concert. It usually consists of a motor with linkages that connect to the wiper arms, all located just below the windshield:

Space tends to be very tight in that area, because the car's instrument panel is on one side and the engine compartment is on the other. The amount of that space, which varies from car to car, is known in the industry as packaging, and it's one of the two major factors that determine wiper configuration. If you see a car with the two wipers facing each other—this is known as the opposed-arm pattern—that probably wasn't the result of an aesthetic choice or a marketing consideration. It more likely had to do with a packaging issue. "The tandem pattern is more cost-effective, but sometimes it doesn't fit," said Patton. "So if you see that opposed-arm configuration, it usually means there was no room for the motor in the middle area."

The opposed-arm format actually provides better wiping coverage, but it requires two motors—one on each side—which presents its own challenges. "You need more high-level electronics to make sure the two motors are synchronized, or else your blades are going to hit each other," said Matt Gausden, director of engineering design and materials at Hyundai. "Also, a dual motor means there are twice as many things that can go wrong. But you get a benefit in terms of packaging, because the motors are farther out on the edges of the car, where there's more space."

However the wiper arms are configured, they must satisfy the other major factor affecting wiper design: federal regulations, as spelled out by the National Highway Traffic Safety Administration. NHTSA standards specify minimum wipe percentages for three regions of the windshield—Areas A, B, and C. While the exact measurements of these zones vary depending on the windshield's dimensions, the three regions, listed from smallest to largest, break down roughly like so:

Area C is the region directly in the driver's line of sight. It must receive at least 99 percent wiper coverage.

Area B is a larger area that includes Area C and a corresponding region on the passenger side. It must receive at least 94 percent wiper coverage.

Area A is a still larger region that encompasses most of the windshield. It must receive at least 80 percent wiper coverage.

"As you're designing and styling the car, there are people who'll check it for engineering feasibility, including those wipe percentages," said Gausden. "If they can't meet those federal requirements, they may have to change the windshield angle and curvature, or even the hood placement. So the wiper system isn't always the red-headed stepchild. It can drive and impact styling regarding hood height and windshield angle."

Interestingly, car makers don't have to submit their wiper systems (or many other regulated vehicle components) to government inspectors. "The United States uses a self-certification system, meaning that vehicle manufacturers must certify that their vehicles, and specific motor vehicle equipment, meet all applicable regulations," said an NHTSA spokesperson. "We do random spot checks, however. We'll go out and anonymously buy cars from dealers in our area and then test them." Of the 33 vehicles NHTSA has spot-checked since 2000, all passed the wiper coverage test.

Meanwhile, why do so many newer cars have one wiper arm that's short and another that's long and curved? This, it turns out, is a result of new trends in windshield design. "The rake or slope of windshields is getting lower, because aerodynamics are becoming more important," said Patton, the Denso executive. "But as the windshield becomes more flat, air can get under the wiper blades and pop them up as you're driving, so you need countermeasures to keep the wipers on the glass. That curved design helps keep the arm tucked down as low as possible."

With so many variables affecting wiper design, that raises a question: are there people out there whose entire job consists of creating wiper systems? "Yes," said Patton. "Here at Denso, our wiper group includes 15 or 20 people for North America, and globally it would be several hundred people."

Hmmm. Could someone even spend an entire career designing wiper systems? "Oh sure," said Patton. "I've had a couple of guys who've gone by 'Mr. Wiper.' It is a very—what's the right word?—a very specific skill set."

And what about Patton himself—did he rise through the ranks of the wiper group? "No," he said, a bit sheepishly. "I came up as a power train guy."

Well, we can't all be Mr. Wiper.