In November 1984, the bridge that carries the MBTA commuter rail tracks over the Danvers River was destroyed in a horrendous fire. The cause was traced to an electrical box in the mechanism that swings the center portion of the span open to allow vessels to travel between the river and Beverly Harbor.

For an entire year, passengers on the Ipswich (the line had not yet been extended to Newburyport) and Rockport branches of the railroad had to be bused between the Beverly and Salem depots.

Given the amount already being spent and the year it took to build a new bridge, one would think this would have been a good time to replace the turning mechanism, parts of which dated back to 1886.

But that would have made too much sense for a state that can spend billions of dollars on a highway project and still end up with a tunnel that leaks like a sieve.

So today, we are left with a bridge deck that's relatively new, but a turning mechanism that is extremely susceptible to damage and which some experts say is badly in need of a $3.7 million overhaul. As of the end of last week, problems with the swing span had required the MBTA to close the bridge to train traffic four times within a month - causing passengers to once again be bused between Beverly and Salem. Many people who commute from the Newburyport, Rowley and Ipswich stations faced delays and hassles getting to and from work.

That's made for some extremely frustrated commuters, many of whom are no doubt looking for an alternative to commuter rail. That's not good for the MBTA or for the environment, since many will likely end up driving to work, rather than relying on public transportation.

Commuter rail is generally a good way to travel and it should be a success, but its success and popularity depends on a reliable system that gets people on and off the train on schedule. Let's hope that the state gets this problem fixed, and that lessons can be learned from it.