On Sunday, September 29, San Diego MTS will add the Copper Line to the trolley system. Instead of a system expansion, this line will replace the Green Line between El Cajon and Santee. Passengers traveling beyond El Cajon will transfer from the Copper Line to the Green or Orange Line in El Cajon.

The rationale for the new line is to improve service reliability, as the segment beyond El Cajon has only a single track, causing delays to both the Green Line and the Orange Line. Additionally, by operating it as a separate route, the Copper Line can use shorter 1 or 2-car trains, reducing operating costs by about $1 million.