East Lyme — The lead drawbridge tender in the bridge control tower sounded the warning siren Monday morning, and less than two minutes later, the new Niantic River Bridge was lowered and locked into place for an approaching train.

The regional train passed by about 11:30 a.m. on the third day since trains began using the bridge.

Peter Finch, the project manager for Amtrak, said switching over to the new track and removing the existing 105-year-old bridge from service late Friday went smoothly. The first train crossed the new bridge around 5:30 a.m. Saturday. Non-passenger trains went across beforehand to check the wires, clearance and signaling system, Finch added.

The roughly 50 trains that pass over daily are allowed to go 60 mph, which is 15 mph faster than the track speed on the old bridge because the new system is much more robust, Finch said.

Amtrak built a two-track, electrified, railroad bascule bridge across the Niantic River between East Lyme and Waterford, 58 feet south of the old bridge.

The old bridge will remain upright but will have to close periodically as the contractor takes it apart. It will be fully removed next spring.

Initially all rail traffic will share one track over the new bascule lift bridge, which could delay commuter trains by up to 20 minutes. Express trains are given priority, Finch said, but the schedules were adjusted to minimize any delays.

The second track is scheduled to be ready in November.

The $140 million project began in April 2010 and remains on schedule to be completed in May 2013.

j.mcdermott@theday.com