Not only was the weather exceedingly nice last weekend - an autumn gem really - but the weather forecasters knew it in time to advise us all in advance. It was predictable, then, that lots of people would take off for the great outdoors. And it was, accordingly, all the more inexcusable the traffic coming back from the Eastern Shore was backed up for an estimated six miles or more at times from the eastern approach to the Bay Bridge on Sunday afternoon and evening - and that doesn't take into account the three lanes of stalled traffic barely creeping across the five-mile length of the bridge itself. The holdup, as usual, was the toll-collection process at the bridge's western exit. But a large part of this particular holdup was that the 10 toll booths were not being put to full use. Exasperated motorists reported that, once on the bridge, it took them up to two hours to reach the toll gates - of which four were handling westbound traffic. Two other gates were programmed for eastbound traffic and four were closed. Yet between 4 p.m. and midnight, an average of 1,800 vehicles an hour were showing up to cross the bridge. According to news reports, officials were caught by surprise - "It's really unusual for this time of year," said one.

Well, we wuppose you could call it unusual - but only in the sense that Indian summer is, by definition, unseasonal. It is, however, a regular event, something you can pretty much count on, and prepare for. And yet the Bay Bridge was only the worst of last weekend's bottlenecks; there were other predictable, trouble spots where extra efforts might have been made to keep the weekend traffic moving more smoothly. Motorists checking out the autumnal splendor of the Skyline Drive, for example, said the traffic lights in and around Gainesville, Warrenton and Front Royal could have been adjusted to ease the flow.

Maybe there are more important matters of public policy in the world. But the question of how to make the most of Indian summer has been much on our minds the past few days, and we have reached a firm conclusion: People who go forth to enjoy a few hours of fresh air and unseasonably warm sunshine shouldn't have to spend equal time, as it were, in a cloud of carbon monoxide.