Few American cities do as well as Chicago has done in terms of providing rapid transit service that covers the city like a blanket; only New York and Washington have systems that provide coverage that’s as dense or denser. But the blanket has some holes in it. The just-passed (but not yet signed by the president) coronavirus relief bill offers assistance to transit agencies struggling to avoid slashing service in the face of continued low ridership. That assistance will come a little too late to keep the Massachusetts Bay Transportation Authority (MBTA) from going ahead with previously announced service cuts that even its own advisory board objected to, but in response to those objections, the cuts the agency approved aren’t as big as they originally were to have been.