DALLAS (AP) _ Union Pacific Railroad will start carrying containers and truck trailers from Chicago to two Texas cities again Monday as the nation's largest rail carrier begins to resume normal service that was disrupted by gridlock.

Six weeks after suspending the service to ease the congestion, one train to Houston and one to Dallas will resume daily service, spokesman John Bromley said Sunday. Northbound service is set to start up again Wednesday.

Union Pacific's year-old merger with Southern Pacific created gridlock along the company's 36,000-mile system that has stranded grain harvests, clogged California ports and stalled production at Gulf Coast petrochemical plants, Northwest lumber yards and steel mills.

The company has said nationwide service should be back to normal by early January.

Most customers have chosen the costlier method of trucking cargo between the affected areas. Bromley said the company wasn't sure how much business may have gone elsewhere permanently during the suspension.

As to how much the service cuts helped, Bromley said, ``it's impossible to quantify. By eliminating some traffic out of that corridor, we opened up the corridor, and also released a lot of locomotives to other service. We felt it contributed.''

The Omaha, Neb.-based railroad, a unit of Dallas-based Union Pacific Corp., is the nation's largest rail carrier.