Disclosures from railroads about volatile oil shipments from the Northern Plains show dozens of the trains passing weekly through Illinois and the Midwest and up to 19 a week reaching Washington state on the West Coast.

The Associated Press obtained details on the shipments Tuesday under public records requests filed with state emergency officials. They offer the most detailed insights to date on the increasing volumes of crude being moved across North America by rail in the wake of a domestic shale oil boom.

The disclosures from railroads also underscore an unsettling fact: Many of those shipments pass through highly urbanized areas where the consequences of an accident would be most severe.

BNSF Railway, for example, reported moving as many as 27 oil trains in a week through Chicago’s Cook County and 13 in a week through King County, which includes Seattle.

The routing of oil trains has become an issue of rising concern after a string of fiery accidents. Those include derailments in North Dakota, Alabama, New Brunswick and Quebec, where a runaway oil train crashed last July in Lac-Megantic and killed 47 people.

Railroads had sought to prevent the public disclosure of the information obtained by the AP, citing security reasons. But the Federal Railroad Administration says the information is not sensitive information that must be withheld from the public to protect security.

Light, sweet crude from the Bakken region of North Dakota and Montana has been involved in most of the major accidents as the crude-by-rail industry rapidly expanded during the past several years.

Each train can carry 3 million gallons of the fuel. Foxx’s order covered all shipments of a million gallons or more.

U.S. Transportation Secretary Anthony Foxx in May ordered railroads to give the shipment information to states, saying it would help first responders and other emergency officials prepare for an accident. 

In Virginia, where a 105-car CSX Corp. train carrying Bakken crude derailed in downtown Lynchburg on April 30, officials revealed last week that 2 to 5 trains carrying at least one million gallons of oil pass through 20 Virginia counties weekly.

Montana officials plan to release information about oil trains in their state today. BNSF representatives have said it’s important for emergency officials to have the information so they can do the proper planning and training, but has urged states to use “discretion” regarding its public distribution.

Some states have agreed to requests from BNSF Railway, CSX and Union Pacific to keep the information confidential. Those include California, New Jersey, Minnesota and Colorado.

Officials in New York, North Dakota and Wisconsin said this week they still were weighing whether restrictions on the information would violate state open-records laws.

Kevin Thompson of the Federal Railroad Administration said Tuesday that officials consulted with national security experts before determining the railroad disclosures do not contain security sensitive information. He declined to answer further questions on how the determination was made.

U.S. crude oil shipments by rail topped a record 110,000 carloads in the first quarter of 2014, according to the Association of American Railroads. That was the highest volume ever moved by rail, spurred by the production of shale oil from the Northern Plains and other parts of the country.

Foxx’s order applied only to Bakken crude and not shale oil from other parts of the country. That’s raised concern from some members in Congress that the government might not be doing enough to prevent accidents.

State officials have been sharing the information on the Bakken shipments with county-level emergency management directors and other local responders who would be first on the scene of an accident.

Associated Press reporter Phuong Le contributed from Seattle.