The Long Island Rail Road, under pressure to meet a 2018 deadline to install a $1 billion crash prevention system, will spend another $1.9 million to outsource some of the work, officials said Monday.

The Metropolitan Transportation Authority’s LIRR Committee on Monday approved the $1,863,919 contract with its positive train control developer, Bombardier Transportation/Siemens Rail Automation, for the wiring and assembly of several communications cases that will house radio transponders installed along the LIRR’s tracks.

The LIRR’s own employees were originally tasked with assembling all the cases. But changes to the project’s original design will require the LIRR to install significantly more of the transponders than originally planned — 108 instead of 60.

And because of delays in the delivery and design of some of the system’s components, “the necessary manpower to perform the additional . . . installations is currently strained,” the LIRR said.

Having the LIRR’s positive train control, or PTC, vendor help assemble the cases will allow the railroad’s work force to install about twice as many at a time and reduce the risk of missing a federal deadline to have the technology in place by December 2018. The LIRR could face fines of up to $25,000 a day if it misses the deadline.

With the Federal Railroad Administration reporting in August that the LIRR had made relatively little progress in installing the PTC equipment on trains, tracks and along its right of way, the railroad recently announced it was beginning installation of some components without having a final design for the system in hand.

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LIRR president Patrick Nowakowski said the railroad continues to “push” developers to get the project done on time.

“We remain very diligent in our efforts to make sure that the deadline is met,” Nowakowski said.

PTC works by having computers on trains communicate with radio transponders on tracks to automatically slow or stop a train when it is going too fast, violating a stop signal, or about to hit another train. Experts have said PTC could have prevented several serious train accidents in the Northeast in recent years.

The MTA Board on Monday took an important step in another key LIRR project. The LIRR Committee approved issuing a request for qualifications from construction firms interested in bidding on a contract to design and build a third track on the railroad’s Main Line.

The LIRR expects to pare the pool of qualified firms to about three or four and award a contract in mid-2017.

The plan, proposed by Gov. Andrew M. Cuomo in January, follows several failed efforts over decades to advance a third track, which proponents say will allow the LIRR to better serve its growing ridership and more easily recover from service disruptions.

MTA Board member Mitchell Pally of Stony Brook said the committee’s vote Monday marked “a day that many of us thought would never happen.”

“This is a very important and essential part of bringing the Long Island Rail Road to the 21st century to be able to provide the service that the people of Long Island not only want, but deserve,” Pally said.

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LIRR officials said they are especially interested in plans to minimize the impact of the project to communities along the 9.8-mile track, which will stretch from Floral Park to Farmingdale. The LIRR expects to release a draft environmental impact statement, listing all those potential impacts, before the end of 2016.