The Central Contra Costa Crossover Project consists of two sections of track crossovers between the Walnut Creek and Pleasant Hill stations, according to BART officials.
The crossover closest to the Walnut Creek station opened earlier this year and the crossover near the Pleasant Hill station opened Wednesday, BART officials said.
BART Director Gail Murray said in a statement, "It was the first time BART cut into the middle of its original tracks and inserted new track crossovers, and the systems to make it work."
Murray represents BART's District 1, which includes the Walnut Creek and Pleasant Hill stations.
With both crossovers in place, BART will implement more 10-car trains during the morning and evening commute hours starting in mid-September to coincide with a planned schedule change, agency officials said.
The crossovers would be used to turn around trains. For example, a Concord-bound train coming from San Francisco with barely any passengers during the morning commute would be routed to the opposite platform through the crossover, BART officials said.
Cars would be taken from the train and added to San Francisco-bound trains that currently have less than 10 cars, providing more seats for riders, according to BART officials.
The trains would then make stops from the Walnut Creek station to Montgomery Street station, then turn back around, BART officials said.
Certain trains will run between the Pleasant Hill and 24th Street Mission stations during the evening commute, according to BART officials.
Currently, there are nine trains that make 13 trips to San Francisco during the morning commute and 11 trips during the evening commute, BART officials said.
Once the new plan starts in mid-September, there will be eight trains making 15 trips during the morning commute and 13 trips during the evening commute, according to BART officials.
The crossover closest to the Walnut Creek station has allowed trains to travel around planned maintenance work on the weekends, significantly decreasing travel delays from 40 minutes to five minutes, according to BART officials.
The Walnut Creek and Pleasant Hill stations are considered the line's two busiest stations along the Pittsburg/Bay Point line, which carries the most weekday commuters in the system, BART officials said.
A video depicting how trains would move through the crossovers to turn back for service and maneuver around disabled trains is available online at https://youtu.be/evVgLZFP5xU.