WHAT EFFECT would an HSR system have on existing transportation patterns? It is possible to speculate based on the experience of the French TGV system.

In September 1981, TGV began a 160-mph service between Paris and Lyon, which in terms of population density and length (250 miles) is analogous to the New York-Washington corridor. TGV rates are competitive with air travel, and the service makes the distance in two hours versus one hour by plane.

The result? Although airline travel in France as a whole has skyrocketed, air travel over the Paris-Lyon route has dropped by half since 1981. In a typical year, TGV also takes 1.8 million passengers off the roads, cutting auto traffic between the two cities by 20 percent.

If a 225-mph maglev system were installed between Washington and New York, the effect on air travel could be even more marked, following the old railway axiom that for each percentage point of reduced travel time, passenger share rises by the same amount.

Interestingly, the airlines might not be unhappy with this development. All three airports in the New York area are at capacity, with overcrowding expected to rise to frightening levels by 2000. HSR could free up valuable landing slots for longer-haul flights. Hartford's airport, for example, could be linked to LaGuardia by maglev, allowing it to serve as a "reliever" at peak periods. Or airlines using specific airports as hubs could replace short-haul flights with maglev service straight from the airport, allowing the diversion of planes and facilities for other services.

Current New York-Washington travel is approximately 55 percent by car, 30 percent by air, and 15 percent by rail. All things (time, cost) being equal, experience has shown that rail service naturally attracts more customers than air. TGV, for example, carried 15.8 million people between Paris and Lyon in 1985, 1.5 million of whom -- according to TGV company statistics -- would not have made the trip otherwise. Nevada estimates that such "induced" travel on their proposed Las Vegas-Los Angeles line would be as high as 28 percent, a fact that -- considering the dollar value of increased tourism -- had enormous significance in the state's plan to go ahead with the HSR project.