Drivers in Cedar Rapids will find some big delays tomorrow. While the Union Pacific repairs its mainline bridge across the Cedar River, mile-long trains will be diverted onto downtown tracks. U-P’s Mark Davis says the problem is low speed limits. While the trains go 60 miles an hour out in the country, they’ll be limited to about ten miles an hour in town. The headaches should be during daytime hours and could cause delays up to 40 minutes. Union Pacific Railroad spokesman Davis says commuters who take downtown streets would be wise to plan ahead.Davis says most trains will simply go around town, and only high-priority trains will be sent down the midtown tracks. He adds the last time they had to divert the trains through Cedar Rapids was 1990.