For the Johns Hopkins University, the breaking point came when consultants showed college leaders photos of campus tours in which prospective students were crossing paths with soda delivery trucks.
At the University of Maryland, the realization arrived more gradually, over the course of countless traffic jams on the congested College Park campus.
But at both institutions, the decision has been the same. Following the lead of colleges around the country, the state's largest private and public universities have embarked on ambitious missions to rid their campus cores of cars - even as more students are arriving at the colleges with their own wheels.
"Schools are realistic and know cars aren't going to go away completely," said Adam Gross of Ayers Saint Gross, the Baltimore architectural firm advising both universities. "But they're trying to build intellectual communities, to encourage people to use bikes, walk, use transit. It's part of an education in being less reliant on cars."
At Hopkins, the campaign began last year with the closing of a main drive that runs from the "Beach" - the circular lawn between the Milton S. Eisenhower Library and Charles Street - and curves north past dorms to the baseball and lacrosse fields. The drive's asphalt was covered with bricks and is now a pedestrian and bike path, open only to emergency vehicles.
The university plans, during the next few years, to close off auto access to most of the south end of the campus, turning the road between Levering Hall, the student center, and Garland Hall, the administrative building, into a pedestrian mall. Traffic will be routed along a redesigned road on the campus' western edge with several peripheral unloading docks for truck deliveries.
The University of Maryland is taking the same approach a few steps further. Its master plan, presented to the Board of Regents this month, calls for closing several internal roads to cars - including the main leg of Campus Drive that runs from the rotary at the heart of campus (the one marked with a large 'M') to the Stamp Student Union and Cole Field House.
The plan, to be implemented during the next few years, would replace cars with an internal shuttle system of frequently running minibuses - which the university lacks - that would link the campus with mass transit and with several parking garages to be built during the next five years.
In the long run, the plan contemplates building a new garage several miles from campus, near the junction of I-95 and I-495. The garage would be linked to campus by a new road that would spare commuters from traveling on congested U.S. 1 to reach campus.
At Hopkins, the move to keep out vehicles is driven partly by aesthetics. With few students bringing cars to the parking-deprived campus, the university was more worried about delivery trucks.
Maryland was motivated by more practical concerns. With an estimated 50,000 cars and trucks entering the campus every day - and with about 23,000 parking permits issued to students and employees - the campus has become nearly impossible to navigate by car at key hours.
"If you try to move around campus by automobile in the 10 minutes between classes, you basically go nowhere because of the gridlock," said William W. Destler, the university provost and a member of the master plan steering committee.
For both universities, there is another reason to reduce traffic: creating more room for construction. Moving cars out of the campus core frees up land used as parking lots for new buildings or green space, officials say.
In advising the two schools, Gross and his colleagues pointed to the University of North Carolina, Princeton University and Emory University, where they also served as consultants, as proof of the benefits of reducing traffic. Although blocking auto access in a car-dependent country always meets with some resistance, they said, it has proved surprisingly popular on campuses.
"You're always dealing with the chemistry professor who wants the gas tank delivered right to his lab, who can't imagine that the beauty of the campus will be worth the sacrifice," Gross said. "Our job is to show him you can do both."
At Hopkins, bicycle use has soared since the road closure - the campus has 20 bike racks, up from three. "It's great - if you're running late for class, you can just go whatever's the quickest way possible, and not worry about traffic," said Alex Forman, a freshman from Colorado who was skateboarding on one of the converted drives.
At the University of Maryland, car owners said they'd be willing to leave their vehicles at the edges of campus if a reliable shuttle system were in place. "I don't have a problem with it - when you walk around campus you see people almost getting hit," said Mike Bengel, a senior from New Jersey who was waiting in his car to pick up his girlfriend on campus last week.
Lenny Sturner, a junior from Severna Park, said blocking auto access would be a hard sell for some car-owning students who "want to be responsible adults and brag about their vehicles."
But eliminating traffic from the campus core would help Maryland feel less like a suburban commuter school and more like the collegiate idyll it aspires to be, he said: "It would add to a more nature-like ambience that the school could really use."