Principally designed and built under the personal, often on-site direction of CPRR's Chief Assistant Engineer, Lewis M. Clement (1837–1914), the original (Track 1) summit grade remained in daily use from June 18, 1868, when the first CPRR passenger train ran through the Summit Tunnel, until 1993 when the Southern Pacific Railroad (SP) (which operated the CPRR-built Oakland-Ogden line until its 1996 merger with the Union Pacific Railroad (UP)) abandoned the 6.7 mile (10.7 km) section of Track #1 over the summit running between the Norden complex (Shed 26, MP 192.1) and the covered crossovers in Shed #47 (MP 198.8), one mile east of the old flyover at Eder. All traffic has since operated over the Track #2 grade crossing the summit south of Donner Pass through the -long Tunnel #41 running under Mount Judah between Soda Springs and Eder. SP made this change because the railroad considered Track 2 and Tunnel 41 (which was opened in 1925 when the summit section of the grade was finally double tracked) to be easier and less expensive to maintain during the harsh Sierra winters than the Track 1 tunnels and snow sheds over the summit.