In July 1993, a Virginia law took effect limiting the number of handguns an individual could purchase to one gun every 30 days. Not to one gun a year, or one gun a lifetime — but one gun a month. The impact of this law on interstate gun trafficking was immediate, it was significant and it is impossible to refute. Prior to the law, Virginia gun dealers were the most important source of crime guns illegally trafficked along Interstate 95, also known as the “iron pipeline” from the Southeast to the states in the Northeast corridor.

The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) routinely traces the origin of crime guns from the location where they have been recovered by the police back to the firearms dealers who first sold the guns. In the 5 1 / 2-year period beginning in September 1989, 14,606 guns that were sold by dealers in one of the eight southeastern states were later recovered by the police and traced to their origin by ATF. An analysis of the trace data that I conducted with my colleague Rebecca C. Knox revealed that the odds that any of these guns would be traced back to a Virginia gun dealer fell by a third after the one-gun-a-month law took effect.

Our analysis, published in 1996 in the Journal of the American Medical Association, showed that the impact of the law on gun trafficking was even more dramatic along the iron pipeline. Specifically, the odds that a crime gun used in the Northeast would be traced to a gun dealer in Virginia fell by two-thirds.

Despite this, the Virginia General Assembly has voted to repeal the one-gun-a-month restriction, and Gov. Robert F. McDonnell has indicated that he will sign the legislation. Their logic appears to be that since exemptions to the law have been created (e.g., for law-enforcement officers and holders of concealed-carry permits), the state should exempt everyone. But there is simply no public health or public safety rationale for repealing the law.

The gun lobby is fond of saying that gun laws only burden law-abiding citizens — that criminals will always be able to get guns. The analysis of ATF’s gun-trace data proves that proposition is not true. The Virginia law applies to retail gun sales, but the impact, both large and immediate, was on illegal gun trafficking. The law places virtually no burden on individuals who are legally entitled to purchase a handgun. It isn’t a prohibition against the purchase or possession of firearms. It doesn’t limit the number of guns an individual can own. It doesn’t increase the time needed to complete a background check. The law burdens gun traffickers and the straw purchasers they hire to supply them with guns, and it makes it more difficult for the rare dirty gun dealer who is willing to look the other way when a single individual walks in to his store asking to buy five or 10 or even 20 or more inexpensive handguns to be sold on the street.

One-gun-a-month’s fate is now in McDonnell’s hands, and one hopes he will take an objective look at the impact of the law before acting. Rather than repealing this law, Virginia should be touting its success to encourage other states and ultimately the federal government to follow its lead and enact similar legislation.

The writer was research director for the Center to Prevent Handgun Violence, which is now known as the Brady Center, from 1994 to 2001.