IT'S HARD TO STOP A TRAIN. Service on the Metra Electric (the old Illinois Central electrification) has resumed a day earlier than expected. A trestle under repair caught fire at a particularly bad time, just before festival week (Taste of Chicago and the downtown fireworks on July 3.) Metra crews expected to be running again by July 2, but had temporary repairs in place this morning. Railroads are subject to all sorts of abuse, from Nature, from truckers misjudging the height of bridges, and from their own equipment taking a dislike to the tracks. Military observers have discovered that bombing tracks generally doesn't disrupt train service for long, because crews have had lots of practice putting unintentional damage right.