If you’re planning to take a road trip this week—Triple A estimates that 42.3 million Americans will do so for the the Fourth of July holiday, up nearly 5% from last year—and you’re planning to drink a frosty beverage during that journey—if a new Dunkin’ Donuts survey is to be believed, 59% of roadsters will stop for food or drinks two or more times during a summer road trip—then you owe Chris Shinouskis a debt of gratitude. She’s the reason you don’t have to balance that Big Gulp or Venti Soy Latte or Yoo-hoo between your legs while trying to keep your hands on the steering wheel. Shinouskis has devoted her career to a very specific part of a car’s design: The cup holders.

Her office in Warren, Michigan, where she works as an “Engineering Specialist for Storage” at General Motors’ Technical Center, is a veritable junkyard of empty containers in every conceivable size and shape. Although she’s never counted, she ballparks her collection at several hundred cans, cups, bottles, boxes, and fast foot soda buckets. “My co-workers are constantly dropping off new containers for me,” says Shinouskis, 50. “They’ll say, ‘Oh, I was at Kentucky Fried Chicken and I picked up a Mega-Cup for you.’ Have you seen this thing? It holds something ridiculous like 64 ounces, which is like a half gallon barrel of pop.” She still has that KFC Mega-Cup in her office, she says, as well as the other Yeti of her industry, 7-Eleven’s iconic 44-Ounce Super Big Gulp.

Although she joined General Motors as an engineer 30 years ago, she’s only been exclusive to cup holders for the past 12. “I migrated to an area in the company called Human Factors,” she says. “Which deals with the things that a customer interfaces with in the vehicle.” One of those things, which she felt wasn’t being given nearly enough attention—and as a mother of three who regularly carpools with thirsty children, something she has a personal investment in improving—was beverage storage. Her job, which technically didn’t exist until she convinced her boss to invent it, involves “translating customer needs into engineering metrics that the design center can work with.” In layman’s terms, she studies cups.

Shinouskis is used to the jokes. “People always laugh, because they think, ‘Cup holders? That’s not a real job,'” says Shinouskis. “But there’s a lot more to it. You have to think about the cupholder within the environment of the vehicle. How is it going to fit with everything that’s surrounding it?” With the increasing number of special features available in modern vehicles—the extra knobs and control panels taking up space—a cup holder has to fight for real estate. “We don’t want a design that basically gives you the choice between using your cup holder or your shifter,” she says. “My job is about making sure everything fits.”

There’s a growing number of differently shaped containers out there—squares and circles and everything in between—and Shinouskis has tried to find ways to accommodate them all. She talks about cup circumference like it’s an art form; an architectural challenge to be outsmarted and outmaneuvered. “Bottles are easy, because they’re a similar diameter throughout the height,” she says. “Cups have what we call a ‘draft’ to it. It changes the diameter as the height increases. Squares kind of mess that up a little. We do have other regions, like China, where they use tea boxes. We just make sure the box has a place to sit, whether it’s within the cylindrical shape of a cup holder or by doing something unique with the cup holder.”

But it’s not always the shape that poses the biggest challenge for Shinouskis. It’s the volume. Cups, not unlike our waistlines, are expanding to hold an increasingly massive amount of fluid. And in the United States, customers want cars with enough storage space for not just one gigantic container of carbonated beverage. “They want two,” Shinouskis says. “And in some cases they want more than two.” But, she points out, plotting adequately-sized drink holders for U.S. drivers is a breeze compared with Europe. “Instead of using multiple smaller containers, their common drink receptacle  is a one and a half liter bottle,” she says. Because it’s used throughout the day, they don’t generally drink from it while driving. “A typical cup holder probably isn’t the appropriate place to store it,” she says. “So what is appropriate? Where do we put it so it doesn’t become a temptation while they’re on the road?”

Shinouskis, as a believer in that old adage “the customer is always right,” tries not to weigh in with her personal opinions on beverage container girth. “Our job is not about telling our customers what they should do,” she says. “It’s about understanding what our customers want and designing to that.” But when asked about the New York City ban on beverages larger than 16 ounces, she can’t hide her personal bias. “It would be much easier for me if we got rid of some of those large sizes,” she says. “But do I see it really happening? No.” The real problem isn’t New York, she says. In many parts of the southern United States, the usual “extra large” cup sizes aren’t large enough for what many drivers are bringing into their cars. “People are in their trucks all day and it’s really hot and humid and they’re drinking a lot,” she says. “There’s been discussion that maybe we need to increase the standard cup holder size to fit a double or even triple Big Gulp.” She pauses to consider this—a grim future of sodas bigger than most passengers—and laughs at the absurdity of it. “I really do hope it doesn’t come to that.”

(This story originally appeared, in a slightly different form, on the Bloomberg Businessweek website.)