ROSEVILLE, Calif. (AP) — Union Pacific said on Monday that it will spend $20 million testing low-emissions locomotives in California.

The railroad may eventually test up to 25 locomotives with various low-emissions technology. They include one, to be based in Roseville, Calif., that will use several emissions-reducing technologies, including recirculating its exhaust gasses.

The railroad and the California Air Resources Board will analyze the emissions reductions achieved by that locomotive over the next year and a half.

Nine other locomotives based in the Colton, Calif., area will also recirculate emissions gasses.

Union Pacific said 15 other locomotives could be outfitted with emissions-reducing technology as testing progresses.

Those locomotives have already had smaller 12-cylinder diesel engines installed to replace their larger 16-cylinder engines, according to Union Pacific spokesman Aaron Hunt. Those locomotives used to be able to haul freight cross-country, but the smaller engines mean they will now be used for shorter trips within California, he said.

A California emissions-reduction program paid $10.3 million toward the cost of installing the new engines, according to documents on the program's website, which said the locomotives were built between 1989 and 1992.

Shares of Omaha, Neb.-based Union Pacific shares fell 32 cents to close at $121.69 amid a broader market decline.