It would run from San Ysidro Transit Center at the Mexico–United States border to Kearny Mesa with a possible extension to Carmel Valley.

The Purple Line could include up to 12 stations, a new maintenance facility, and a storage yard.

With its mode being changed to higher-speed and higher-capacity commuter rail, a new study will eventually be conducted to determine how many more daily trips will be generated.

[5][6][7] In April 2019, SANDAG approved the final version of a November ballot initiative to increase the countywide sales tax by a half-cent, which further detailed future transit plans and specifically mentioned and estimated the cost to build the proposed San Ysidro-Kearney Mesa trolley extension.

As a commuter rail line, trains could run as fast as 110 miles per hour (180 km/h).