Wow, what can I say but “Don’t get K.P. started on one of his fantastical sidetracks”. [(-D]
The BNSF would save minimal mileage for its direct traffic between SoCal and the PNW by a ‘Barstow Cutoff’. A Devore LH connection says ‘oops, we built that expensive third track up Cajon Pass for nothin’. A LH connection with the UP at Summit will be very difficult and expensive to build. At any rate, UP won’t want them on Their cutoff even with some 2MT. Bottom line is, this traffic will stay routed on the 2/3MT transcon via Barstow.
The main traffic bottlenecks are in the Tehachapi mountains where improvements may be funded by Caltrans (ha ha) and BNSF - see the map for details. UP can’t even justify spending $$ on its own railway there!
EDIT - Vern, just noticed you’re new to Trains.com - Welcome! You may have not seen this epic topic on BNSF Cajon Pass Triple Tracking by this topics originator K.P. Harrier - it will be a good read for you - see you in a week [swg]