The number of abortions plummeted by 50% in one out of every five counties in Texas, where an onerous abortion law caused the distance to the nearest clinic to increase by 100 miles or more, according to a new study.

The study, published online on Thursday in the Journal of the American Medical Association, examined the impact of house bill 2, a 2013 Texas law that forced more than half of the state’s clinics to close.

The study compares the number of abortions obtained by local women in 2012 to 2014, the year after HB2 took effect. In 56 counties, most of them concentrated in west Texas, the distance to the nearest abortion clinic increased by a hundred miles or more.

The study offers further evidence that the law originally justified as a health measure was in fact a powerful tool for preventing women from accessing abortion. HB2, in the guise of making abortion safer, required abortion clinics to meet expensive, hospital-like standards and medical professionals to be on staff at a nearby hospital. The US supreme court ruled last June that there was no medical justification for these requirements and thus they were unconstitutional.

The decision has caused federal courts to strike down similar laws across the south and midwest and effectively prevented other states from following in Texas’ footsteps. But in Texas, the changes wrought by the law have been profound and lasting. By the time the justices handed down their decision, the number of abortion clinics had dropped from more than 40 in 2012 to just 17. The state’s remaining abortion providers face steep barriers to opening new clinics and restoring those numbers.

The study found that the numbers of abortions obtained by local women also dropped in counties that experienced smaller changes in distance to the nearest abortion clinic. In the 33 counties where the distance increased from 50 to 99 miles, the number of abortions fell by almost 36%. Even a slight change in distance could provoke a drop in the number of terminations: in the 55 counties where the distance to the nearest clinic increased by only up to 24 miles, the number of abortions fell by 12.7%.

Meanwhile, in counties that saw no change in the distance to the nearest abortion clinic, the number of abortions fell by less than 2%.

The new study comes from four researchers with the Texas Policy Evaluation Project (TxPEP), of the University of Texas at Austin, which examines the impact of government restrictions on reproductive rights. It is the most detailed examination to date of the impact of clinic closures in Texas on the number of abortions.

Its finding are in line with a different study, released on Tuesday, which found that the proportion of pregnancies ending in abortion has reached historic lows. That study found a strong link, albeit not a conclusive one, between the decline in the abortion rate and better contraception use. But it also found a connection between the declining abortion rate and laws like HB2, which impose onerous restrictions on abortion clinics and cause them to close.

These laws, which reproductive rights activists call Trap laws, for “targeted regulation of abortion providers”, were the only type of abortion restriction that seemed to produce a consistent decline in the abortion rate. Trap laws place expensive or difficult and medically unjustified requirements on abortion clinics, with the aim, according to abortion rights supporters, of forcing clinics to shut down. The dozens of other abortion laws passed in recent years, such as increased counseling requirements designed to dissuade women from having abortions, seemed to have little to no impact on the rate of abortion.

“Our study gives further insight into the ways that the clinic closures due to Texas’s restrictive law resulted in an undue burden on women seeking access to abortion care in Texas,” said Dr Daniel Grossman, one of the TxPEP researchers and an OB-GYN at the University of California, San Francisco. “It corroborates the findings of our previous qualitative research, where we heard from women that the long distances to the nearest clinic created significant financial and logistical barriers to care.”