The Dublin MetroLink has moved a step closer, after the planning application was submitted to An Bord Pleanála.
The application from Transport Infrastructure Ireland (TII) is for the rail route.
MetroLink consists of a new fully segregated railway, most of which will be underground, between Swords and Charlemont areas in the city.
The route will also serve Dublin Airport - the first rail link to the country's largest airport - as well as major education facilities.
The Department of Transport says MetroLink will connect to more than one million people by interchanging with rail, DART, Luas and bus services.
Construction is set to begin in 2025, with a view to it beginning operation in the early 2030s.
Transport Minister Eamon Ryan said this marks a key stage in its development.
"In July I secured Cabinet agreement to progress the major MetroLink project.
"I am delighted that today we have met our commitment with the submission of a planning application for the route.
"MetroLink is a flagship project, but it is also one of a suite of major public transport investments that we have secured ongoing funding for within Budget 2023".