Slip switches combined 4 junctions and a diamond, in the space normally reserved for one junction.  They allowed for a very compact interlocking when reducing space was important.  But they made for a very complicated interlocking.  West Detroit had numerous slip switches in it's heyday but by 2000 they had been reduced to a few.  This photo, taken in December 2001 from the cab of an eastbound locomotive, gives a good view of the remaining West Detroit slip switches, before they were removed in 2003.   The Detroit downtown skyline is visible in the background.  

[John Boehl photo]

West Detroit

Conrail