More than a dozen companies and business groups, urged by railroads including Union Pacific Corp., are warning regulators that cutting speeds to 40 miles an hour from 50 would have a cascading effect, delaying other trains sharing the tracks carrying cargo such as furniture, grain and electronics.

“It would impact the whole rail system, is what it will do,” said Will Higman, chief operating officer for Reliable Wholesale Lumber Inc., a family-owned business in Huntington Beach, California, with about 100 employees. Slower trains would add days to a two-week trip for wood from Canada, raising costs and frustrating customers, Higman said in an interview.

Regulators in the U.S. and Canada are considering rules to prevent accidents involving trains hauling crude oil, such as one that killed 47 people in Lac-Megantic, Quebec, last year. Carloads of crude surged 40-fold since 2008, which safety advocates say poses a risk to communities near the tracks.

In addition to new speed limits, proposals have been issued to require sturdier cars that are less prone to puncture.

Some tank-car makers and companies that lease the cars, including Trinity Industries Inc., have said the standards will cost more than regulators anticipate and will push more shipments onto trucks, increasing highway traffic.

Safety advocates say the speed limits and other proposed regulations are important to cut the risks of hauling crude. The U.S. Transportation Department is reviewing more than 1,000 comments submitted on the proposed standard. Final rules may be issued this year or in early 2015.

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