Bridge Engineering – LIRR Post Avenue

Standout Features

McLaren Engineering Group provided bridge engineering design services for this $9.7 million project to replace the Post Avenue Bridge in Westbury, NY – which serves as a connector for the Long Island Rail Road. As part of the LIRR upgrades, the Third Track project was approved to add a tertiary track to 9.8 miles along the congested Main Line of the LIRR between Floral Park and Hicksville. The first completed project initiative since the Main Line Expansion Project has been the Replacement of the Post Avenue Bridge in Westbury, NY.

Originally built in 1914, The LIRR Post Avenue Bridge was a 63-foot single span structure carrying two tracks supported by steel thru plate girders with a concrete deck and reinforced abutments made of concrete. The 100+ year structure has been a conduit for train traffic that cars and buses pass under with an original roadway clearance of only 11 feet 10 inches. The dimensions had made it extremely vulnerable to vehicular strikes, particularly from trucks failing to clear the underpass. Although still considered in good condition, the bridge was struck over 80 times, causing numerous train and roadway delays in both directions.

The McLaren Difference: Applied Ingenuity

McLaren Engineering Group in association with Halmar International was awarded the $9.7 million Long Island Railroad design-build contract for the replacement of the Post Avenue Bridge. As engineer-of-record, McLaren was responsible for completing the final design by expanding preliminary work developed during the RFP process. McLaren was tasked with designing the replacement of the two-track bridge with a three-track bridge and increasing the vertical clearance to 14 feet to reduce outages. The team effort required extensive planning and precision to keep the project on schedule and within budget.

Five months prior to replacement, the bridge superstructure began to be assembled in a parking lot adjacent to the bridge on temporary shoring towers in order to minimize rail disruptions. As part of this design-build contract, McLaren was responsible for completing the final design in order to provide LIRR with the most economical design with the least amount of impact to the community. The new bridge was installed entirely during a 48-hour weekend track outage. Throughout this meticulously planned 48-hour period, the existing bridge superstructure was rolled out and the new superstructure was rolled into its new position via self-propelled modular transporters (SPMTs) from the adjacent parking lot. Crews from Halmar International, Inc. worked around the clock using a unique construction method with a remote-controlled lifting device. That transporter lifted the 103-year-old bridge, which remained intact after it was cut away from its connection to the abutments, and placed into an adjacent parking lot. The contractor then had to modify the abutments to support the new bridge height. Then, the new bridge was lifted, in its entirety, and put into place over the roadway.

Work was completed in just 36 hours, all timed down to the minute to ensure no disruptions to the first train of the Monday morning rush hour. Additional work to fully complete the project included adjustments to the station platforms, installation of stairs and concrete painting and sealing work. The roadway underneath the bridge is being re-graded to provide improved sight lines for motorists, enhancing safety and meeting the latest design standards and requirements of the New York State Department of Transportation.

The project was completed ahead of schedule and within budget due to the amount of collaborative planning involved. The LIRR Post Avenue Bridge is now 50 feet wide — 13 feet wider than its predecessor — a width that allowed for a section of third track to be placed with a clearance of 14 feet. Traffic disruptions were minimized and a strategic plan to accommodate commuters during the 48-hour rail shutdown was accomplished. The industry-wide collaboration of many moving parts proved to make the entire project a huge success.

This project was awarded the 2020 Engineering Excellence Platinum Award in Category C: Structural Systems by the ACEC New York and the 2018 Project of the Year by the American Society of Civil Engineers, Long Island Branch.