U.S. railroad company Union Pacific Corp said on Monday that a rail line on which a train derailed in northern Colorado was back in service. The line, which is used about once a day, connects Windsor, which is in the Niobrara shale play in northeastern Colorado, as well as other towns in the state. The train, which was heading from Windsor to an East Coast destination, spilled 5,300 gallons of oil on Friday morning. Over the past several months, the industry has been under heightened government scrutiny due to an increase in train derailments involving oil tank cars. The amount of oil moving by rail from shale formations has risen sharply because the region is not well-connected to pipelines.