President Obama has signed a bill giving railroads at least three more years to upgrade train safety technology.

The White House says Obama signed the legislation Thursday. The bill also extends until Nov. 20 the government's authority to spend money on transportation programs in an effort to buy time for Congress to pass a long-term bill.

The measure was sought by the rail industry, which said many railroads were likely to miss a deadline for installing the technology, known as positive train control or PTC. Railroads had seven years to install PTC. They now have until Dec. 31, 2018, to complete the upgrade or seek a waiver.

Federal investigators say PTC would have prevented an Amtrak derailment in Philadelphia last May that killed eight people and injured about 200 others.