Amtrak has slackened its regulations to allow passengers to carry firearms with them on a limited number of trains.
The US train operator has previously banned guns on all trains since the September 11 attacks.
The new law follows restrictions similar to those imposed for air travel. Firearms must be stored in checked bags and placed in a locked and hardened container.
However passengers can only carry the guns aboard a train and into a station that offers checked baggage service. Amtrak runs about 300 trains a day nationwide, and less than a third offer checked baggage service.
The new law was passed by Congress last year after a senator from Mississippi was able to get support for a proposal to force Amtrak to allow guns or risk losing its funding.
Congress approved the proposal but gave Amtrak more time to comply with the new mandate.
Amtrak has subsequently spent months planning the new initiative, and has paid about $2 million to change its reservation system, install secure storage areas at checked baggage stations and modify 142 baggage cars.
“We think it’s reasonable for people who are going on hunting trips or going to winter homes and are traveling on Amtrak to have the right to transport their firearms just as they would on an airplane or in their cars,” said Rachel Parsons, spokeswoman for the National Rifle Association.
Amtrak spokesman Marc Magliari said he is confident that changes made on the trains will keep guns safely secured. He said Congress gave Amtrak the time it needed to make the needed security adjustments.