He knew the commute was getting to him when he began sleeping under his desk on those nights when he worked so late that the trains ran infrequently.
"As horrible as it sounds, I could have bought a house in the suburbs," he says. Or he could have taken another job offer, in Washington.
Instead, something happened that represents an extraordinary trend for Philadelphia, which for decades had been trying and failing to stem the loss of its most promising graduates.
Bentley's bosses started talking about a move back into the city, where the company was founded in 1985. At a meeting in May, staffers learned that management was opening a satellite office for as many as 50 workers at 1601 Cherry St.
Two days later, Kerr was unpacking his belongings in his new work space - after a 13-minute bike ride from the house he has bought in Powelton Village.
"Since I was in high school, there's been such an amazing amount of positive growth in this city," he said one day this week at Capriccio's, an outdoor cafe along the Benjamin Franklin Parkway. "There's so much diversity, so much going on."
I was looking for someone like Kerr. He puts a face to an astonishing figure I came across recently.
Between 2000 and 2009, Philadelphia added 16,032 people ages 25 to 34, with a college degree or more, to neighborhoods within three miles of the city's center.
That's better than Washington did. Or Atlanta, Seattle, San Francisco, or Chicago. Only Boston and New York City added more of these holy grail residents.
Here's one take, from Paul Levy, president and CEO of the Center City District:
"Between Girard and Tasker, Front Street and 43d Street, it's a totally 21st-century city."
Good jobs are the driver, Levy said. "You've had huge growth in high-skill positions in large and small firms."
Here's another take, from David Hollister, Bentley's financial officer:
"We're a tech company, a software company, and new, fresh, energetic ideas are what we need. Some of the young professionals . . . would prefer to live in the city, so we figured it was time."
For the city, this development translates to real dollars. This fall, Philadelphia officials hosted representatives of the three major credit-rating agencies, and shared a series of impressive numbers - not just the increase in educated young people, but also the nearly 10 percent hike in household income over the last decade and the 156,000 students of higher education who lived in the city in 2010 - more than in Boston.
The views of Standard & Poor's were of particular interest, since the agency two years ago gave Philadelphia a BBB credit rating, which is relatively unimpressive. Afterward, S&P increased the city to BBB-plus with a "positive" outlook.
And that let the city borrow $96 million this April while paying less of a premium, Treasurer Nancy E. Winkler says. That adjustment produced savings of about $4 million.
Kerr told me about another colleague who will calling Philadelphia home soon. Programmer Mark Dane plans on moving his office from Exton to Center City within weeks. The former West Philly resident has put a 1920s rowhouse in Northern Liberties under contract. Bye-bye, Downingtown.
"I missed the city," he said. "I missed being able to walk out my door and see people on the sidewalk. Here, I'd walk out of my apartment complex and maybe see someone if they were walking to their car."
Contact Daniel Rubin at 215-854-5917, firstname.lastname@example.org or on Twitter @danielrubin.