Complex sentence: DB Schenker has a policy of only operating air braked trains, whereas many trains operated by WCRC use vacuum brakes, which meant that DB Schenker was unable to operate those charters in place of WCRC.
Split into simpler sentences: DB Schenker has a policy of only operating air braked trains. Many trains operated by WCRC use vacuum brakes, which means that DB Schenker is unable to operate these charters in place of WCRC.