As politicians call for more crude-by-rail safety measures, Valero recently defended its plans to bring up to two 50-car trains per day of Bakken crude from North Dakota to its refinery here...[R]efinery officials said the project -- which would allow Valero to import up to 70,000 barrels of crude per day by rail -- would benefit the economy and the environment by creating jobs and reducing emissions from smoggier boat deliveries of oil...Valero officials...tried to ease concerns about fiery rail accidents. They highlighted the city's finding that transporting oil by train carries a lower risk of spills than marine shipments. Project opponents, however, have questioned the study, which relies on safety data before the crude-by-rail boom in recent years. The Union Pacific trains traveling between Roseville and Benicia would always be attended, Cuffel said, unlike the runaway oil train that exploded and killed 47 people last year in Lac-Megantic, Quebec.