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The Pricing Plan

By Carmen Nobel  |  Posted 2008-02-21 Print this article Print

New York, London, Seoul and other major cities are desperate to eliminate traffic gridlock. Congestion fees may provide relief, but Zipcar co-founder Robin Chase believes she has the perfect wireless solution. 

The Pricing Plan

Mesh networks—including those used in municipal Wi-Fi deployments—dynamically route data packets among wireless access points. Only one access point must be connected directly to the wired network, with several others sharing a connection over the air. In urban Wi-Fi networks, these nodes usually sit on rooftops and lightposts. In Chase’s plan, each car would become a node in a dynamic mesh network, routing and repeating packets of data. The nature of the mesh guarantees there is no single point of failure.

In most congestion pricing plans, including the one New York is proposing, the fee is a set rate determined by time of day and by whether a car enters a certain cordon, or geographic belt, during peak hours. Bloomberg’s leading plan calls for a per-use fee of $8 for cars and $21 for trucks that enter Manhattan below 86th Street between 6 a.m. and 6 p.m. weekdays.

For congestion pricing, a mesh would make it relatively simple for cities to expand—and contract—the pricing cordon gradually, without much additional on-street hardware, Chase says, because drivers would install the wireless boxes in their own cars.

Further, a mesh would enable a system that could measure actual congestion, charging cars according to real-time density rather than arbitrary geography, she adds.

Because her vision relies on open-source technology, Chase was chagrined to see that New York’s “request for expressions of interest” (a precursor to a request for proposal) called for a system that can interoperate with E-ZPass—the proprietary, RFID-based electronic toll-collection system employed on most toll roads in the northeast United States. Thousands of commuters already have E-ZPass transponders in their cars.

She’s hoping that cities considering congestion pricing will also consider driver privacy. As popular as E-ZPass is, it raises the ire of civil libertarians who complain that states don’t always dump individual tolling data from their systems. In fact, E-ZPass records emerged last summer as a popular way to prove infidelity in divorce court: The records could prove that a car and its driver strayed from their usual path, according to Associated Press reports.

To that end, Meadow Networks has developed a “locational privacy” protocol that promises to compute the tolls for a particular driver without being able to reconstruct the driver’s route.

“Most of the existing mechanisms that try to preserve locational privacy do so after the fact,” says Roy Russell, senior consultant at Meadow Networks, former CTO of Zipcar and Chase’s husband. “They rely on discarding information, scrubbing logs, erasing details that are used to create invoice entries, etc. They don’t really preserve locational privacy; they just try to delete the information after it has been collected. They still leave trails, however. Just imagine a bill with each individual line item that shows which toll you went through and how much it cost.

“The Meadow Networks mechanism is quite clever and relies on cryptography and ‘zero-knowledge proofs,’” he says. “It is possible for the tolling authority to know how much you owe while at the same time not know where you traveled and what individual tolls you incurred. So it protects your locational privacy and ensures that you pay the tolls at the same time.”

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