With so much reason for rejoicing about progress on the $104 million expansion of the Tower 55 rail junction southeast of downtown Fort Worth, it takes a pretty gloomy person to focus on the dark cloud on the horizon.Still, that cloud is there.The news this week is that railroad officials say the project is progressing quickly and could be completed by September. That means the four tracks that intersect there — two east-west tracks owned by Union Pacific, a north-south track also owned by Union Pacific and another owned by BNSF Railway — could see congestion relief soon.A third north-south track is under construction, to be owned by BNSF.The junction is named for the old switching tower where operators once controlled the traffic flow. That job is now done remotely by people watching computer screens.The intersection currently handles about 90 train crossings a day, mostly freight, but also Amtrak passenger trains.It’s been common in recent years for trains to be backed up for miles waiting to get through. That means residents of some neighborhoods to the north see intersections blocked for long periods.Children have been known to crawl under or between rail cars to get to school.The extra 9,000 feet of track will allow trains to move through more quickly.Financing includes a $34 million transportation grant and contributions from Union Pacific and BNSF.What’s the dark cloud?Railroad officials say the work will allow for about 10 years of growth and expansion of their business.But what happens in 10 years? Will Tower 55 be back to its old, congested self, the only difference being the additional trains backed up on the track that’s being laid now?Railroad and local transportation officials discussed several plans before announcing the current expansion — elevated tracks, below-grade tracks, even routing trains around Fort Worth. The unifying theme was that each option was very expensive and posed significant engineering challenges.Ten years will go by pretty fast. If the railroads grow like they plan, Tower 55 will be congested again before we know it.There’s no time like the present to plan what to do next.