Zollars has been the head of Yellow since 1999 and has been president of Yellow Freight System since 1996. Prior to joining Yellow, Zollars was senior vice president of Ryder Integrated Logistics, a division of Ryder System Inc.
ProLogis said Zollar is replacing John E. Robson, formerly senior advisor with Robertson Stephens, who stepped down from its board to accept the presidential nomination to serve as CEO of the Export-Import Bank. Robson, 70, joined the ProLogis Board in 1994.