Yep, the Westside would kind of be one, using a lose definition.. So would the Intercal, via the El Centro main, through Mexico, and back to the Sunset line at Algodones. Rhe El Paso and Southwestern also served as a kind of secondary main, even having long distance passenger services via Douglas AZ.

Maybe one of the last big "secondary" mains also a kind of "cutoff" (a two-fer?) that the SP constructed, or "re-constructed", and then connected directly into Pasadena Junction, and to the Shops, under Mission Road, and to El Monte, on the Alhambra line, via the El Monte "flyover", was the State Street line, in 1974. This was the former PE San Bernardino main line down the middle of what became the San Bernardino Freeway (I-10), which is now the Metrolink San Gabriel Subdivision, serving the SGV-San Bernardino commuter trains.