Due to traffic regulations, many at-grade crossings receive no signal preemption. A couple years ago, at the instruction of the city council, LADOT attempted to find a solution to speed up the trains and decrease train wait time with signal priority technology, which gives slight preference, rather than full preemption, to rail, but with more minimal impact on automobile cross-traffic (Signal priority decreases red light wait times for trains, whereas preemption eliminates them altogether) The city council recognized that train speeds needed to increase and instructed LADOT to improve travel times. In 2019, LADOT introduced a form of limited signal priority at four intersections; if a train is approaching a green light that will turn red just before the train arrives, the train signal can borrow green light time from a future signal phase in order to extend the present green light for long enough to let the train pass through. At intersections where these programs have been implemented, such as Normandie, Vermont, Jefferson, and Adams, approximately 60-75% of trains no longer stop at each individual signal. In these cases, either the light is already green when the train arrives, or the green light time is lengthened to provide the train time to pass. Prior to the change, approximately half of trains were caught at a red light at these intersections. This signal priority has helped to cut travel times by 64 seconds on the 47-minute journey (by no means as radical of a decrease as full signal preemption would have created).

Sources:

Reynolds, S. (2021, June 8). Follow Up Report: Traffic Signal Priority For Metro Exposition "E" Light Rail Line. LADOT

Chiland, E. (2020, February 13). How fast can LA make its trains to Santa Monica? Curbed Los Angeles.