It will probably take 10-15

[spdrun]

It will probably take 10-15 years to do. Meanwhile, there’s a perfectly good rail line running along the coast about 2.5 miles away.

It looks like the UTC blue line extension will share the Coaster’s right-of-way for much of the way, making a lot of it easy to build.

San Diego Plans Extension to Its Trolley Network, Mostly Skipping Over Inner City

So building a long divergent right-of-way to Carmel Valley would likely be more expensive and time-consuming.

It’s a shame that the Blue Line isn’t being built now. With improved signaling and train control systems, the trend is for regulators to grant exceptions to allow lighter rail cars to use “heavy” rail lines.

Blue Line should have had shared/interchangeable tracks with the Coaster line and been electrified at 25,000 volts A.C. (world standard) or 3,000 volts D.C. (if they didn’t want transformers in the cars) not at lower trolley voltages. Done right, it could have been a back-door way to start electrifying the main coast line towards LA.