Trains are expected to roll along a northwest Shawnee County, Kansas, track late Wednesday evening, three days after a derailment collapsed a Union Pacific bridge, a company spokesman said.

Crews worked today to complete a temporary bridge spanning Soldier Creek. UP spokesman Mark Davis said the company hopes to return train traffic to the busy corridor by late Wednesday.

Union Pacific engineers are in the beginning stages of developing a plan for the permanent replacement bridge, but it won't be in place for several months, he said.

"The focus is to repair and reopen," Davis said. "The next will be to redesign and rebuild."

Davis said investigators haven't determined what caused 38 rail cars to derail late Sunday near N.W. 70th and Valencia Road and fall into the creek. The rail had been visually inspected earlier that day, and more extensive tests had been conducted earlier in the month.

Investigators will try to determine whether soggy ground contributed to the derailment. National Weather Service records show Topeka received 0.83 inches of rain Saturday and another 0.07 inches Sunday.

"Soil conditions are always looked at, rain or not," Davis said. "That's one of the things taken into consideration."

Davis said about 150 workers -- from UP investigators to private contractors -- continued working at the site today. Crews from surrounding states brought heavy machinery to the scene late Sunday to begin the cleanup process.