Gov. Mark Dayton is joining the chorus of voices demanding a full environmental review of a possible rail connection in Crystal that would reroute mile-long freight and "high hazard" oil trains south through Minneapolis along Theodore Wirth Park.

BNSF and Canadian Pacific tracks now cross each other in Crystal, but do not connect. Adding a connection would allow eastbound freight trains to turn south. Trains would slow to 25 miles per hour to navigate the turn, potentially blocking five intersections in Crystal and Robbinsdale at the same time.

In the letter to Deb Miller, the acting chairwoman of the Surface Transportation Board, Dayton wrote that the federal agency that oversees rail construction has "the legal responsibility to ensure a full and timely environmental review."

Specifically, Dayton is asking that the railroads not be allowed to use an exemption process outlined in federal law.

A BNSF spokeswoman said creating the connection is "routine and on a smaller scale than the construction of new mainline track."

"The proposed new connection directly impacts the cities of Crystal, Robbinsdale, New Hope, Golden Valley, Plymouth and Minneapolis because a high volume of mainline traffic, including High Hazard unit trains originating in the Bakken oil fields, would be diverted onto a lightly constructed and maintained single track line," Dayton wrote. "This traffic would travel through downtown Minneapolis and residential communities that have not previously been exposed to such traffic."

Dayton said he shares concerns about the potential effects of the proposed diversion of rail traffic, including increased noise and vibration, decreased vehicular and pedestrian safety, simultaneous blockage of grade crossings, delay of emergency vehicles and "exposure to High Hazard unit trains."

Leaders in Crystal and Robbinsdale and of the Minneapolis Park and Recreation Board have all sounded the alarm about the possible connection.

Canadian Pacific's line now carries as many as two dozen freight and oil trains a day, while the BNSF line, which runs along Bottineau Boulevard, serves only two short trains a day.