Like all good Boston commuters, even those who don't, technically, drive in from the South Shore, I was furious to learn the new Liberty Tunnel shaves only three minutes off the morning rush hour trip from Braintree into the city.

And if there's one thing that bugs me even more than the minuscule dividend we're reaping for all those hours spent in Big Dig traffic, it's this: While people like me will inevitably fritter away the daily 180-second morning bonus, the goody-two-shoes among us will be busy making themselves and the world better with their little time savings.

They'll be reading James Gleick's celebrated new biography of Isaac Newton, a few pages at a time, and rubbing your face in all the interesting things they're learning. ``I didn't realize that he discovered the optics of color!'' they'll chirp, as you search your mind for grade-school factoids about the man.

The Pollyannas will spend their found time flossing, writing thank-you notes, performing simple one-minute stretching exercises at their desks, balancing their checkbooks.

You'll see them seeking out the lonely guy in the tech department to inquire, ``How's it going?'' - and then actually listen to his response.

Even more annoying, they'll exude a newfound calm behind the wheel. When questioned about why they didn't go Russian when the !@#$ driver in front of them refused to blow through a red light so they could too, they'll smile and explain they just take the time spent waiting for the light to turn back to green out of their three-minute earnings.

Me, here's how I look at this supposed time savings: It's going to be used against us. You gotta figure that by now your boss probably has seen the data on commuting times collected by Smart Route Systems, and he or she will expect you to start coming into work, if not on time, at least three minutes less late than you were before.

But actually it's going to be harder than ever to get to work by the start of business. Knowing you have three extra minutes, you'll linger just a little longer over coffee and the ``Today'' show, and then - oops! - you'll get caught up in thinking about Katie's hair, or checking out the crowd gathered outside the studio and wondering who would stand in the broiling sun - and next thing you know, you're 10 minutes behind schedule.

Of course, you could make up the 10 minutes on the other end of the day, since the report by Smart Route Systems found that the evening rush hour commute dropped from 25 minutes down to 15.

But, hey, if the time has to come out of your own pocket, what good will the $14.6 billion Big Dig do you at all?