Control technology will make subway service faster, safer.

Hordes of commuters and tourists are voting with their feet n favor of the discount transit fares offered by Metrocards and free transfers between bus and subway lines in New York City.

While this has achieved the goal of encouraging the use of mass transit, crowding on subway station platforms has become so severe, according to recent media stories, that conductors are hard pressed to even close the subway car doors.

But help is on the way. Six companies, including mine, have entered bids with the Transit Authority to introduce communications-based train control technology that will make New York City's subways safer, faster and more reliable.

Among other major benefits, subway platform congestion should be reduced because trains will be able to arrive as frequently as every 90 seconds. That would be good news to the real estate industry, especially to building owners in the congested Wall Street area where, along with the daily commuting workforce, a growing number of people are living in office buildings converted to residential use.

While it is "next generation" technology for the New York subways, communications-based train control isn't new. Alcatel pioneered the technology 30 years ago and now has systems in revenue operation at 23 sites around the world. Last month, the Port Authority of New York and New Jersey awarded a contract for the JFK rail link to a consortium that includes Alcatel. We will supply our communications-based train control technology for the operation of this new and important airport rail line.

The signaling technology currently in use on the subways is essentially the same that was put in place when the first line went into revenue service in 1904.

While transit employees working in signal towers throughout the system control the track switches, operation of the subway trains rests entirely with the train operators. The current signaling system attempts to control operation of the trains through a rigid system of manual train movement. This is far from perfect.

This system separates trains by fixed blocks - pre-determined lengths of track which create the "headway" or safe operating distance between trains. To insure that a moving train does not collide with the train ahead of it, the blocks contain mechanical devices that are designed to trip the brakes and stop a train that overrides the block separating it from the train ahead.

One of the more significant problems with current fixed block signaling is that safety is not pro-active. In 1995, a train on the Williamsburg Bridge crashed into the rear of another train, killing the operator and injuring 54 passengers. The National Transportation Safety Board later determined that the operator had fallen asleep and ran through the safety stop at high speed. The train crashed before it could stop.

Similarly, in 1991, an operator running his train at high speed ran through a safety stop near Union square. The train brakes set, but the train jumped the track and crashed into the tunnel walls, killing five passengers and injuring numerous others.

In effect, the system worked, but did not avert collisions.

But more important for daily operating efficiency, fixed block technology does not allow for adjustments in frequency of train service at rush hour. As a result, subway platforms are jammed by riders waiting for the next train. Common sense dictates that if trains could arrive and depart quickly while still maintaining a safe headway, crowding would be alleviated.

Equally frustrating for passengers are the times when trains are held at or between stations for no apparent reason, especially when a train is close enough to a station where passengers could get off and find an alternative mode of transportation. But the inflexible operations of fixed block technology dictate this procedure.

The solution to fixed block limitations began appearing in the early 1970's when the first communications-based train control systems were put in service in Europe by Alcatel. In this system, a wayside computer communicating with computers on board each train is constantly aware of and is monitoring the locations and speed of all trains on the system, pro-actively controlling their operation as well as their movement.

The computer adjusts the headway spacing between trains according to their speed and the position of other trains, whether they are running or stopped. Because the block between the trains in this system is not fixed but is constantly monitored and adjusted by the computer to maintain an appropriately safe operating distance, this system is called "moving block signaling."

The train's computer slows or stops a train when it detects that the train is exceeding the speed limit, and can be configured so that the train driver cannot override the computer's orders. Had Alcatel's moving block technology been in place on the New York subways, neither the Williamsburg Bridge nor the Union square wreck would have occurred.

While the safety features of communications-based train control are impressive, what will mean the most to commuters is the short time between trains at rush hour.

With ridership on Re subways likely to go even higher when unlimited use weekly and monthly Metrocards are introduced, the Transit Authority is moving in the right direction to make the system meet the demand placed on it.