In a blur of white, a Peugeot 205 swerves in front of the visitor's car, its passengers gesturing wildly to show there are drugs for sale.
For thousands of young people who head for the Netherlands with drugs in mind, the next stage is simple - follow the "runner" in his car to a Rotterdam backstreet lair and agree on a price."These guys cut us up in their car, lights flashing, then started making joint-rolling and coke-sniffing gestures," said Briton Jon H. "The game goes on like this until you give them either the thumbs up or the finger."
Anyone driving north from Antwerp on the A1 motorway in a car with French or Belgian license plates can expect a similar unsolicited offer.
"It's very good marketing," said Detective Superintendent Albert Hagen, head of Rotterdam police narcotics unit, who says competition among pushers is forcing them to take to the highways to promote their wares.
"Drug tourists" pour over Dutch borders, drawn by the Netherlands' tolerant attitude to possession. The cheapness of the product makes it attractive to commute to score.
"The coke here is about 30 or 40 percent cheaper than London and much purer," said Steve D., an advertising manager from Britain.
On the streets of Amsterdam a gram of moderate-quality cocaine, diluted perhaps only to 30 percent, costs $65, compared with London prices of $90 to $105 for inferior quality, he said.
Steve D. and thousands like him are giving Dutch authorities a headache, but they keep coming while drugs are cheap.
"It doesn't matter from which direction you approach Rotterdam, the runner will pick you up," said Hagen. He doesn't like it but has few ways to stop them.
Runners never carry drugs, and arresting them for dangerous driving is a poor deterrent in this high-stakes game.
To get a conviction, undercover officers use unmarked cars with foreign licence plates and wait for a proposition.
But Hagen said he lacked the resources to mount this type of operation on a scale that would drive the runners off the streets.
In common with the Dutch government, he blames the stricter laws of the Netherlands' neighbors rather than the lax Dutch regime as the cause of the problem.
"What can we do? Close the border? What about a borderless European Community?"
This thought has haunted the Dutch throughout the debate over a Europe without borders and led the French to argue strongly against the Netherlands becoming the site for Europol, the European Community's fledgling police headquarters.