UP 48" AreoWedge #948001 - [2014 Winter Solstice Study] - Designed by UP employees to reduce drag on the forward end of a double stack train, the areo wedge was "[y]ears in development, [and] the Arrowedge® is the latest innovation in Union Pacific's ongoing commitment to design, build and implement fuel-saving technologies" (from to UP's marketing propaganda).
Introduced on their Long Beach to Joliet Illinois stack trains, the wedges started to appear in August of 2013, and this one is mounted on an eastbound stack drag heading towards Yuma Arizona.