“A new vendor used to mean someone’s cousin coming in from Egypt,” said Zach Brooks, whose blog Midtown Lunch chronicles the sidewalk-food scene. “Now it’s a major culture clash.”

The early summer has brought at least a dozen new trucks, many of them run by people with advanced degrees and white-collar backgrounds: CupcakeStop is owned by a 2009 New York Law School graduate. Cravings, a Taiwanese food truck, is the brainchild of Thomas Yang, who developed the truck’s business model before graduating from Baruch College in 2008. The owners of Street Sweets both left six-figure jobs to build their business, and the Big Gay Ice Cream Truck is driven by Doug Quint, a doctoral candidate in bassoon performance at CUNY. “The whole Brooklyn Philharmonic season was canceled,” he said. “I have to get through the summer somehow.”

The new truckers, knowingly or innocently, often roll right over unwritten rules about which corner belongs to whom, and when. The city, other than blocking certain streets entirely and enforcing parking regulations, does not dictate locations for food carts. But spots are virtually owned by vendors who have worked them for decades; they are handed down within families and even sold on the black market.

“You can set your watch by it: park in a new spot, and within 15 minutes someone will come and check you out,” said Kim Ima, a former actress who owns the Treats Truck. Ms. Ima, one of the first upscale mobile vendors, had the tires of her truck slashed near her bakery soon after opening in 2007. “The street is like the playground when you’re a kid, and you have to learn your way around,” she said. “You have to learn where the sixth graders sit and where the dodgeball game is before you can safely sit and eat your lunch.”

Vendors say that the traditional code of the streets may be effective, but that it feeds on fear, intimidation and the city’s lack of enforcement of permit rules.

“It only works because everyone is a little bit in the wrong, and no one is 100 percent clean,” said Mr. Lao. “We can’t go through legal channels to resolve our disputes.” Mr. Lao was referring to the notorious black market in the food vendor permits issued by the city’s Department of Health. Most of the vendors interviewed would not talk publicly about the status of their permits. But several of them, asking not to be identified because of the dubious legality of the arrangements, said they had secured theirs by paying unauthorized “fixers” or by entering into partnerships with existing permit holders. A common form of retribution among vendors is to report one another to city authorities for permit violations.

The black market, vendors say, is nourished by the city’s bureaucracy. Many, especially those for whom English is not a first language, pay brokers to navigate the system. These illegal go-betweens are common in the central depots where food vendors are required by the Health Department to park their carts and trucks.