IT WON'T make the holiday best-seller lists, but an intriguing report on migration patterns of capital area commuters is out -- offering statistical fodder to support all sorts of inconclusive and sometimes conflicting theories on life in the not-so-fast lanes and underground as well. In this latest anatomy of a commuter, another in a series of biannual studies by regional transportation experts at the Metropolitan Washington Council of Governments, the central figure seems to be the Solo Driver. The lone motorist is commuting into and out of central employment areas -- the District, Ross-lyn, the Pentagon and Crystal City -- in greater numbers. That clogs roads, which makes this commuter a villain in the eyes of all other commuters, as well as those who study this stuff.

But that's only part of the story. It turns out that more commuters than ever are piling into subways. Then add this finding: the number of commuters bunching up in cars is down. This leads the study to ask, "Why, after a major investment in Metrorail, expansion of high-occupancy vehicle lanes and promotion of ride sharing, have we not been able to reduce the proportion of persons traveling to the core area in single-occupant automobiles from the 33 percent observed in 1977?" This is a multiple-choice test, and any choices you make are part of the answer:

(a) The investment in Metrorail has obviously helped considerably. Its percentage increase in ridership is far greater than the percentage increase in the total number of commuters.

(b) People like to go door to door in the comfort of their cars, on their very own schedules, even if they can't qualify for HOV lanes.

(c) Many people don't live anywhere near mass transit -- or even near people with work habits like theirs.

(d) Some people get subsidized or free parking at work, making it even more attractive to go it alone.

(e) Others are willing to pay quite a bit to park, either because they have to or because they would rather fight than switch from car to bus to subway and back every day.

The one-word answer is convenience -- and neither carrots nor sticks are going to turn too many hard-core soloists into groupies. Eliminating parking perks may help. Subsidizing those who use Metro may help just as much. Reasonable HOV rules, too, encourage group riding. Additional and adjusted bus routes and the completion of the full 100-plus-mile rail network should attract even more riders. But overly stiff parking fees and taxes can drive some employees out of the central job area entirely -- eventually nudging more and more businesses to the outer suburbs. And though flexitime or staggered government hours may ease some traffic flows, it may well create more solo drivers who can't or don't find neighbors with their schedules.

Hitting the right combination of options is no mean feat, which makes the periodic findings of the council of governments all the more valuable to the local, state and federal officials as well as private employers whose decisions are so unrelentingly interdependent.