The long-under-construction subway arrives in a famous part of town.

A dig in 2023 exposes the guts of LA under one of the city’s busiest intersections. COURTESY OF LOS ANGELES COUNTY METROPOLITAN TRANSPORTATION AUTHORITY

Los Angeles deserves its reputation as the quintessential car city—the rhythms of its 2,200 square miles are dictated by wide boulevards and concrete arcs of freeways. But it once had a world-class rail transit system, and for the last three decades, the city has been rebuilding a network of trolleys and subways. In May, a new four-mile segment with three new subway stations will open along Wilshire Boulevard, a key east-west corridor that connects downtown LA to the Pacific Ocean. What today can be an hours-long drive through a busy, museum-­packed stretch of the city will be, if all goes well, a 25-minute train ride.

The existence of subway stops in this part of town—known as Miracle Mile—is a technological triumph over geography and geology.…