Complex sentence: An expansion to Reno, Nevada on the UP line over Donner Pass has been considered, which would add a stop in Truckee, already served by the "California Zephyr".
Split into simpler sentences: An expansion to Reno, Nevada on the existing UP line over Donner Pass has been considered. This would add a stop in Truckee, which is already served by the "California Zephyr".