Three future Metro transit projects may be built sooner rather than later under a plan announced Friday.

The Los Angeles County Metropolitan Transportation Authority is bringing private investors on board to help with three different projects:

Designing and building a train through the Sepulveda Pass

Building a light-rail line from downtown Los Angeles to southeast L.A. County cities

And creating additional pay lanes on crowded freeways

Although listed for funding under Measure M, the one-half cent sales tax approved by voters in November, the projects are not scheduled for completion for years, some even decades.

By adding private cash up front, the county transportation agency can start designing next year and possibly complete these projects earlier than scheduled.

“By creating innovative partnerships with the private sector, we can accelerate Measure M projects and ease traffic across our region even more quickly than we expected,” L.A. Mayor and Metro Board Chairman Eric Garcetti said in a statement.

The three public-private partnership projects and their private partners were announced Thursday by CEO Phil Washington at the Metro board meeting:

Parsons Transportation Group Inc. and Cintra US Services will join with Metro on the Sepulveda Transit Corridor, but only on the 11-mile train portion. That project is scheduled to be completed in 2033. Any additional carpool or pay lanes element connecting the Westside with the San Fernando Valley would be a separate project, said Pauletta Tonillas, Metro chief communications officer.

Skansa and Kiewit agreed to work on the West Santa Ana Branch Transit Corridor, a 20-mile light-rail from Artesia to downtown Los Angeles. Metro has scheduled breaking ground in 2022.

Goldman Sachs will participate in bond underwriting to help with building more ExpressLanes, freeway lanes that charge tolls to single-occupancy drivers. Carpoolers are charged less or zero. ExpressLanes currently exist on the 10 Freeway from El Monte to Los Angeles and the 110 Freeway from South Los Angeles to the 105 Freeway in Norwalk.

Public-private arrangements would add funding up front so Metro doesn’t have to wait for the tax revenues to accrue. The partnerships would also bring on private planners and designers who can suggest faster, more efficient methods, as well as require a payback plans, Tonillas said.

“It’s kind of a concept of a home mortgage. Not many of us have all the money to buy our homes upfront. So we work out an arrangement with the bank … then we pay the bank back over a long term period,” she explained.

Often a project using private funding will add tolls as a form of payback, she said.

Metro will work on project proposals that would include these private partners. No timetable was given.