▁out ▁of ▁these ▁locomot ives ▁they ▁were ▁replaced ▁by ▁Ein heits d ampf lo kom ot ive ▁(" standard ▁steam ▁locomot ives ") ▁of ▁class ▁ 6 4 ▁and ▁ 8 6 ▁based ▁in ▁Stuttgart ▁until ▁the ▁mid - 1 9 6 0 s . ▁These ▁were ▁replaced ▁by ▁class ▁ 2 1 2 ▁dies el ▁locomot ives ▁based ▁at ▁K orn west heim . ▁ ▁In ▁September ▁ 1 9 8 0 , ▁the ▁S - B ahn ▁S 4 ▁opened ▁between ▁Mar bach ▁and ▁Stuttgart - Sch w ab straße . ▁The ▁original ▁ 2 0 - min ute ▁interval ▁service ▁was ▁increased ▁to ▁a ▁ 1 5 - min ute ▁interval ▁service ▁in ▁ 1 9 9 6 . ▁The ▁S - B ahn ▁service ▁uses ▁class ▁ 4 2 0 ▁electric ▁multiple ▁units . ▁ ▁Until ▁ 8 ▁December ▁ 2 0 0 8 , ▁services ▁on ▁the ▁eastern ▁section ▁Regional bahn ▁ran ▁from ▁Mar bach ▁to ▁Back n ang ▁during ▁peak ▁hours ▁at ▁ 3 0 - min ute ▁interval ▁and ▁hour ly ▁at ▁other ▁times . ▁On ▁S atur days ▁Regional bahn ▁trains ▁ran ▁hour ly . ▁These ▁used ▁a ▁class ▁BR ▁ 4 2 6 ▁electric ▁multiple ▁unit . ▁The ▁additional ▁service ▁in ▁the ▁pe aks ▁used ▁a ▁class ▁BR ▁ 1 1 0 . 3 ▁with ▁three ▁Sil ber ling ▁carri ages . ▁On ▁Sund ays ▁the ▁places ▁between ▁Mar bach ▁and ▁Back n ang ▁were ▁served ▁only ▁by ▁bus . ▁ ▁Since ▁ 8