When Honolulu was a less populated place, the general rule for behavior on the road was to assume that the driver you encountered in an irksome situation was somebody — a guy who worked at the shop your uncle ran, a woman whose daughter went to high school with you or a neighbor from down the street on the next block.

Even when there were no clear connections, you didn’t cut off another driver, lean on the horn, yell, much less flash the bird, because somehow, sometime, somewhere you’d come across that somebody again, or someone else who’d seen you act like a jerk.

That someone will soon be the police department after HPD installs on its patrol vehicles cameras to capture license plates as cars range the roads of Oahu.

Law enforcement officials will not be looking out for rudeness, but for patterns that might indicate criminal conduct.

The department is following the lead of cities and states on the mainland that have put up cameras and scanners on buildings, utility poles, bridges and police vehicles to “capture” images of their citizens’ cars.

They assemble and store data as a “reactive investigative tool,” according to Yonkers, N.Y., authorities, to catch bad guys and to gather evidence for prosecution. Many share their data about comings and goings with other agencies.

These cameras are not the kind aimed at the broad width of the H-1 Ewa-bound so people can check if traffic is backed up at the Punchbowl offramp, but closeups of drivers’ license plates as they turn into the Nordstrom parking garage at Ala Moana Center, depart for the less ritzy retailings of Don Quijote, then to a mental health clinic.

These tools have the blessing of the federal government, which bestows grants on police departments as part of the comprehensive fight against terrorism. Though narrower in scope, local watchful eyes mirror the government’s wide circle of surveillance across the Internet and telecommunications networks, which may soon be tested in lawsuits that contend it violates privacy and constitutional rights.

Advocates for vigilant surveillance will argue that more good than bad emerges, that if people are not engaging in illegal activity, they have nothing to fear.

This doesn’t mean that law enforcement should be allowed a free hand.

To its credit, HPD is devising a set of rules for its data-collecting program. These rules will determine how long information can be held. The department also says it has no plans to share data with other agencies.

That’s a good start to safeguard citizens. However, legislation — not internal rules — should govern these activities to allow people an avenue for redress, to assure their rights are upheld and that procedures and adherence to them are not concealed.

There is need for law enforcement to collect information. But the City Council, Mayor Kirk Caldwell and, more important, citizens should be the main participants in determining police conduct in using a razor-edged tool.