Electric utilities in Colorado have watched their coal supplies drop in recent months because of clogged capacity on the nation’s rail lines. The congestion’s biggest impact so far is on coal transport, but other commodities such as oil, grain and manufactured goods also are experiencing shipping delays.

Federal regulators and grain shippers are particularly concerned about capacity constraints as this year’s wheat harvest is piling up at shipping terminals.

Utilities still are working to rebuild supplies that fell below normal levels last winter.

Xcel Energy, Colorado’s largest power supplier, said it suffered “a bit of a shortage” in the first half of this year when rail operators couldn’t deliver enough coal.

Fort Collins-based Platte River Power Authority said it has been “moderately impacted over the past nine months by railroad performance.”

Neither utility was forced to curtail generation, but their coal stockpiles fell below levels they seek to maintain in the event of supply disruptions.

Nationwide, a shortage of trains, tracks and rail workers are producing sporadic supply disruptions for a number of industries.

Part of the shortage stems from a surge in domestic crude oil production, some of which is transported in rail tank cars.

Analysts say other factors include an improving economy that is pushing demand for rail transportation, and the severe winter of 2013-14 that hampered rail operations.

“All these factors can congest the entire railroad system. It is a very slow process to bring things back into acceptable performance,” said Lee Boughey, a spokesman for Westminster-based Tri-State Generation and Transmission Association.

Like Xcel and Platte River Power Authority, Tri-State declined to say how much its stockpiles have been depleted by the rail backlog. Tri-State said it “continue(s) to work with the railroads to ensure adequate delivery of coal to our power plants.”

Capacity constraints have attracted the attention of the U.S. Surface Transportation Board, the chief federal regulator of rail operators.

“The Board has been closely monitoring the rail industry’s performance metrics and is concerned about service problems across the nation’s railroad network, particularly on the Canadian Pacific Railway Co. and BNSF Railway Co. systems,” the agency said earlier this year. “The board members have written to CP and BNSF to express concerns that poor service is negatively affecting agricultural, coal, passenger, and other traffic.”

BNSF responded with a plan to spend a record $5 billion this year on equipment, system improvements and new workers.

The Surface Transportation Board said it is particularly concerned about grain transport, with a backlog of shipments from last year’s crops and large amounts of new grain coming in from above-average harvests this year in many parts of the country.

The agency ordered BNSF and CP to file weekly reports on their progress in clearing backlogs.

In a July 18 report, BNSF said 6,329 of its wheat cars were listed as “past due,” defined as more than three days past a shipper’s desired transport date. The past due cars, on average, were 24.2 days late.

BNSF and Union Pacific are the largest rail operators in Colorado. UP is not being required to file backlog reports.

Colorado wheat growers weren’t affected much last year by rail constraints because the wheat crop was smaller than average, reducing the need for transport, said Darrell Hanavan, executive director of the Colorado Association of Wheat Growers.

But with this summer’s harvest estimated at 86.4 million bushels, nearly double last year’s 44.3 million bushels, rail capacity could become an issue.

Eighty percent of Colorado’s wheat crop is shipped out of state by rail, mostly for export to Asia and the Mideast.

At a shipping terminal in Byers, Cargill has filled its 720,000-bushel elevator with wheat and is now piling incoming deliveries on the ground as it awaits rail cars.

Terminal manager Michael Moore said a shortage of rail cars is an annual occurrence during and after the wheat harvest.

Wheat miller Ardent Mills, which recently established its corporate headquarters in Denver, said it hasn’t yet experienced any impact from rail delays but is preparing contingency plans.

“We are working with our customer base to anticipate any supply chain disruptions as a result of slowed rail transportation,” supply chain vice president Jeff Zyskowski said. “We are utilizing our network of mills and various modes of transportation to ensure there is no disruption in delivery … for both inbound grain to our facilities and outbound product to our customers.”

Booming production of crude oil also is stressing the nation’s rail system. Colorado output has more than doubled since 2008, to 177,000 barrels a day in 2013.

Anadarko Petroleum, one of Colorado’s largest producers, said shipping capacity is tight but production has not slowed.

New pipelines coming online this year are expected to ease rail tightness, Anadarko spokeswoman Robin Olsen said.

Steve Raabe: 303-954-1948, sraabe@denverpost.com or twitter.com/steveraabedp