[5] Los Angeles County Transportation Commission acquired the Southern Pacific Railroad Burbank Branch in 1992.

[7] It was incrementally extended to Claremont that December, Montclair the following February, then finally to San Bernardino in May 1993.

By December 2015, SANBAG decided that this second phase of the project, from the San Bernardino Transit Center to Redlands, would no longer be a Metrolink extension, but rather an independent system.

[citation needed] SANBAG planned to use diesel multiple units (DMUs) and have Omnitrans operate the system.

Omnitrans was removed as the system's operator in 2019 amid mounting deficits, and Metrolink took over construction and procurement.

[27] Arrow's DMU sets have been studied for wider deployment on the rest of the San Bernardino Line.

The Los Angeles County Metropolitan Transportation Authority (LA Metro) has plans to add the current LA General Medical Center station on the El Monte Busway as an infill station to the line.