THE EVIDENCE is incontrovertible that red-light cameras save lives and could save many more if they were in wider use. They do so mainly by deterring and reducing the number of side-impact accidents, known as T-bone crashes. The rancorous, misguided debate over the cameras, which capture images of vehicles as they run through red traffic lights, is now settled. The District and other cities are well justified in expanding the deployment of such life-saving equipment.

A definitive new study by the Insurance Institute for Highway Safety shows that in 14 big cities where the cameras were in use, including the District, the rate of fatalities stemming from red-light crashes fell three times faster than in 48 cities that did not install the cameras. What's more, the institute, a nonprofit group funded by the insurance industry, found that the cameras saved 159 lives in the 14 cities over five years starting in 2004. If the cameras had been in use in every big American city, 815 lives would have been saved during the same span, the researchers concluded.

Those findings will be discomfiting to the scofflaws and libertarians who have long believed they have a God-given right to run red lights without the nuisance of risking a fine. They have felt put upon that the government is somehow invading their privacy by training cameras on intersections or "profiting" from the resulting fines. Never mind that in the great majority of cases, the real victims are not the drivers who ignore the red lights; rather, they are the pedestrians, cyclists and drivers of other vehicles who are run over, rammed, maimed and killed by the red-light runners.

The rationale for red-light cameras is firmly grounded in common sense. Police can't be everywhere, and officers should not be diverted from high-crime areas to police every high-risk intersection. As practically anyone who travels in and around the District can see for themselves, drivers tend to decelerate and exercise caution in red-light and speed-camera zones - which are listed on the police department's Web site. The result: slower-moving traffic and fewer fatal accidents.

Gnashing their teeth at Big Brother's supposed intrusion, opponents of the cameras have argued that the cameras violate their privacy or that local governments use them simply to generate revenue. But there are plenty of examples of government levying fines to promote public safety - think of hunting violations, or unsafe job-site conditions - and there's no greater reason to impugn officials' motives in deploying the cameras than any in other areas of public safety administration.

Opponents have also cited studies linking the installation of red-light cameras to an increase in rear-end collisions. But the more important point is that the cameras have sharply reduced T-bone crashes, which are far more dangerous and cause more deaths.

The real question for those who continue to complain about the cameras is: What is the alternative? Do they really want to remove the cameras and accept hundreds more deaths in order to save red-light runners from paying fines of $50 or $100? By that calculus, opponents of red-light cameras must value life very cheaply indeed.