By Chris Dunn & Donna Lieberman — So far, public debate about Mayor Bloomberg's congestion-pricing proposal has focused on issues like the specific boundaries of a congestion-pricing zone, the fees drivers will pay, the impact on mass transit and how much congestion pricing will actually reduce traffic congestion.

Lost in this discussion has been the fact that implementation of congestion pricing could involve the creation of a massive system of surveillance cameras.

Like the program already in place in London, the congestion-pricing plan being considered here would use cameras to read and record the license plate of every car, truck and motorcycle entering or leaving the congestion-pricing zone, as well as of many vehicles traveling inside the zone. The system then would match that license plate information against a database of vehicle owners to bill drivers the congestion-pricing fee.

This type of plan raises enormous privacy concerns. A system of thousands of cameras would allow the government to build a massive database of the daily movements of the hundreds of thousands of people who drive around Manhattan. Also, it would create the infrastructure that could open the door to even broader tracking of pedestrians.

Consideration of this scheme comes at a time when surveillance cameras are proliferating in New York City - on the streets, in our schools, in public housing, on transit systems and elsewhere. And just as the number of surveillance cameras is increasing, so, too, are the technical capabilities of cameras, which now can capture the most private of information from considerable distances.

Given the privacy threat posed by a camera-based congestion-pricing program, the city must carefully consider alternative ways to reduce traffic that do not require massive (and costly) tracking systems. And should the city ultimately choose to proceed with a congestion-pricing scheme that uses cameras, any such plan must include stringent privacy protections to assure that a program to reduce traffic and protect the environment does not become a vehicle for blanket video surveillance and a massive database of the innocent comings and goings of New Yorkers. Without reasonable safeguards, your trips to doctors, homes or businesses may all be recorded by the government and available to the police.

For starters, the images collected must be strictly limited to the license plate of the vehicle. Camera design and operation must ensure that the system cannot capture images of people traveling in vehicles, images of the cars' contents or images of nearby pedestrians or residences.

Next, any plan must guarantee that information collected will be used solely for collecting tolls. This massive database cannot become a treasure-trove of information for the police, credit card companies, immigration authorities, the IRS, employers, private eyes or disgruntled spouses.

And those people who do not want to end up in a government database every time they go to work or drive into the city to see a play must be given an option that would allow them to pay any congestion-pricing fee without being videotaped, as through the use of "camera-free" toll lanes. And to minimize possible privacy violations, information collected through the system should be retained for only the minimum period of time.

Finally, any congestion-pricing plan must provide for independent oversight of the camera system and database to assure that privacy rights are not being violated and for clear complaint procedures for individuals concerned about privacy violations.

With a commission charged with reviewing the mayor's proposal now hammering out the details of a congestion-pricing plan, now is the time to draw the line when it comes to surveillance cameras. Cameras can, of course, serve useful purposes, but they also pose the enormous risk of exposing our daily and lawful activities to constant - and permanent - government scrutiny.

Dunn is associate legal director and Lieberman executive director of the New York Civil Liberties Union.