SAN DIEGO — The San Diego Association of Governments and Caltrans will begin three nights of overnight closures of northbound Interstate 5 Tuesday night after completing overnight work along southbound I-5 ahead of schedule.

Work crews will close northbound I-5 from state Route 52 to Genesee Avenue from 9:30 p.m. to 5 a.m. each night though Thursday, according to SANDAG. The closures are necessary to remove wooden structures that supported the recently completed construction of a trolley overpass at Voigt Drive

Neither agency expected to begin closures of northbound I-5 until later this month or early July due to similar work on a trolley overpass spanning southbound I-5 at Nobel Drive, which began June 9. Those closures were expected to last until June 28 but concluded early last Tuesday morning. SANDAG expects to conduct additional closures of northbound I-5 June 23-27.

The closures are part of the $2.17 billion Mid-Coast Trolley Blue Line Extension, which includes a planned 11-mile extension of trolley service by San Diego's Metropolitan Transit System from Santa Fe Depot in downtown San Diego to University City. The extension will add trolley stops in Mission Bay Park, UC San Diego and Westfield UTC. SANDAG is receiving $1.04 billion in funding from the Federal Transit Administration to complete the project.

The extension and related projects are intended to reduce traffic congestion as the county's population increases. Construction on the extension began in 2016 and is scheduled to be completed in 2021.