"I'm glad you're back," the officer says, throwing the cruiser in gear.
The milkman returned to the Philadelphia area in August, when Mast's Lancaster company, Doorstep Dairy, added the far-western suburbs to its old-timey routes.
Not since 2007 has the metropolis seen a milkman. That's when Rosenberger's gave up delivery, six years after giving up its glass bottles.
Changing habits, technological innovation, and industry consolidation squeezed milk delivery. What's driving its comeback is a combination of nostalgia, the farm-to-table craze, and Karen Mast, who said yes to her husband's latest big plan.
"I'm always coming up with ideas," Daryl says in the cab of his blue-and-white 2007 Isuzu delivery truck, as we're trying to read the street numbers on cul-de-sac mailboxes. "I run them by my wife, who just listens, then shoots holes in them. This one she just latched on to."
On this night, one of three a week that Daryl delivers, he was relying on Google maps and a GPS device to find his newest customers, 68 households around Downingtown and Exton. He'd been up for 18 hours and wouldn't be in bed for seven more.
"It's not exactly ideal," the father of three young boys said. "I'm juggling a lot at the moment." The margins are tight, and he's not ready to hire a second driver for his two-year-old business. His wife and mother help in the office. They have hired a part-time salesman and marketer, Jeremy Leaman, who's responsible for customers like Richard Whiteford of Downingtown's Williamsburg development.
One day about two weeks ago, Whiteford, 66, was sitting on his front porch, writing a speech about global warming. The environmental activist says he liked Leaman's low-key pitch, and, as the young man spoke, Whiteford's mind danced.
"I was remembering - the thickness of the bottles, the sound of them clanking together. I grew up on a farm, and we had 58 cows we milked. I was remembering the smell of fresh milk right out of a cow."
Whiteford likes the idea of supporting local farmers. His wife raves about the milk.
So does Meadow Smith, who, like Whiteford, has been taking delivery for only two weeks. She, too, left a giant iced cooler outside her door Tuesday night and awoke to find fresh skim and whole milk and a dozen brown eggs.
"My kids are so picky with their milk - they can tell the difference between Wawa milk and Rosenberger's milk. If I get another brand at the grocery store, they can tell. They won't drink it."
But they devoured a half-gallon of Doorstep Dairy's milk in half a day. The milk comes from Guernsey cows on Warwick Manor Farm in East Earl, Lancaster County. Yoder's Country Market in New Holland does the bottling.
Mast grew up on a dairy farm himself. His grandfather had a grocery store that made deliveries. Doorstep combines the two ideas, and from 11 years of livestock hauling, Mast can tap a community of local farmers for his products.
He's the first to explain that the milkman of 2012 is not for everyone. His product is expensive. A glass gallon of whole milk costs $3.75, plus a $2 deposit. The delivery charge for Downingtown or Exton is an additional $3. At the Wawa, where he takes his nightly coffee break, a gallon jug of whole goes for $4.05.
"We don't try to compete with the supermarket. We need to push the local product, a premium product. You know where it's coming from. We try to connect the consumers to the producers."
There's a certain irony, he says, in delivering fresh milk to subdivisions built on land that was once farms. He's hoping there's also money in it.
To see a video of the Doorstep Dairy delivery, go to www.philly.com/milkman
Contact Daniel Rubin at 215-854-5917, firstname.lastname@example.org, or follow on Twitter @danielrubin or Facebook at http://ph.ly/DanRubin.