Do Storrow Drive lane closures add to greenhouse gas emissions?

The most common complaints that I have heard about the Storrow Drive lane closures center on either the safety concerns associated with closing one lane of a major highway (to allow parking for a few dozen cars during a concert) or on the slightly sour-grapes basis of why should a tiny convenience for a few lazy drivers cause such massive inconvenience for thousand of others. You are quite correct, however, that it also dumps huge quantities of unnecessary greenhouse gas into the atmosphere and perhaps that's the biggest concern.

A typical automobile uses gasoline most efficiently when it is traveling between about 30 and 60 miles per hour. At speeds below about 20 to 30 miles per hour (including idling at a full stop) it uses about a gallon an hour and a gallon of gasoline produces about 20 pounds of greenhouse gas (so-called carbon dioxide equivalent). If you were stuck for an hour or so, your engine wasted approximately one gallon of gas. Normally you would zip through in a matter of minutes and use perhaps a tenth of a gallon.

So, if there were 1,000 motorists like you, about 20,000 pounds, or 10 tons of unnecessary emission were delivered into the atmosphere over Boston. If 10,000 motorists were similarly inconvenienced, then 100 tons of nasty pollution were dumped into the atmosphere. That's a lot.

Of course many approximations and assumptions go into this sort of estimate and it could easily be wrong by a factor two in either direction, but it does give you the uneasy feeling that we probably should not be slowing traffic down, or stopping it for no good reason. And that includes many traffic lights and drivers who leave their cars and trucks idling, as well as Storrow Drive lane closures.

Dr. Knowledge is written by physicists Stephen Reucroft and John Swain, both of Northeastern University. E-mail questions to drknowledge@globe.com or write Dr. Knowledge, c/o The Boston Globe, PO Box 55819, Boston, MA 02205-5819.