Possibly, if there is a change. If so, it will be phased in, and the reduction in diesel demand may make it more economical to retain a mix.
If any are interested in the LNG train topic:
Chesapeake presses natural gas locomotives despite resistance by railroads
http://www.platts.com/weblog/oilblog/2012/03/28/chesapeake_pres.html
Westport Reports Second Quarter Fiscal 2012
http://www.stockhouse.com/News/CanadianReleasesDetail.aspx?n=8580032
Westport and Caterpillar Inc. have agreed to co-develop natural gas technology for off-road equipment. While the agreements initially focus on engines used in mining trucks and locomotives, the companies will also develop natural gas technology for Caterpillar’s off-road engines
More LNG Locomotives in Russia
http://www.fleetsandfuels.com/fuels/lng/2012/06/more-lng-locomotives-in-russia/
EMD to develop natural gas locomotive
http://www.railwaygazette.com/news/single-view/view/emd-to-develop-natural-gas-locomotive.html