Only one of the two people movers is now regularly in operation at Pittsburgh International Airport, the latest in a series of cost-cutting measures.

A three-car train shuttles passengers and airport personnel through a half-mile tunnel that connects the landside and airside terminals while the other train on a parallel guideway is used on alternating days.

Allegheny County Airport Authority spokeswoman JoAnn Jenny called it a pilot program to determine if the airport could operate efficiently while reducing people mover costs. The experiment began Aug. 7 and is to continue indefinitely.

Some passengers have complained, saying they face a wait twice as long as when both trains were in service and sometimes have to wait for the next trip because of rush-hour crowding. Although the wait may be only several minutes, time is critical for late-arriving passengers or for those delayed by security.

"We've had a couple of e-mails from travelers, but once we explained what we're doing, they were somewhat more understanding," Ms. Jenny said.

It represents the latest cutback in a facility where relocated operations by US Airways, fewer flights overall and a tight economy have meant unused gates, vacant boarding areas, blocked-off concourses, less foot traffic and lower airport mall sales.

The move comes at a time when travelers who start and end their trips here has soared from 6.2 million passengers two years ago to 8.2 million this year. But the increases haven't come close to offsetting losses in connecting traffic caused when US Airways dropped Pittsburgh as a hub. The airline is down to 58 daily departures, compared to more than 600 at one time.

Ms. Jenny said although only one people mover is being used, the other is ready to go should the need arise, which hasn't been the case thus far.

"So the train isn't really out of service, it's just sitting in idle," she said. "We're working with the Transportation Security Administration, Bombardier [the people mover builder and operator] and our facilities operations people and constantly monitoring the situation."

She said airport officials picked August to test a single-train operation because it's typically busier than many other months and they wanted to make sure one train could accommodate everyone.

However, at the request of the airlines, the authority will be running two trains into at least early next week in anticipation of heavy vacation and business travel, Executive Director Bradley D. Penrod said yesterday.

"We will run two trains into the weekend and then early next week, then go into alternating mode as traffic warrants," he said.

A three-car train can handle about 150 at a time on a 63-second, computer-controlled one-way trip between the airside and landside terminals. Counting the time while people exit and board, a round trip takes a little over three minutes, with the train reaching a 32 mph speed.

Ms. Jenny said that it's too early yet to determine the cost savings, mostly from reduced electricity usage. If the program becomes permanent, airport officials would likely renegotiate Bombardier's contract to operate and maintain the system. Without the people mover, there is no passenger access between the two terminals other than using another tunnel where people could walk in an emergency.

In 2000, when times were more promising for the airlines and Pittsburgh International Airport, officials spent $9.5 million to renovate the four original people mover cars, build two more cars and expand the two stations to accommodate three-car trains.