This　paper　considers　the　optimal　control　problem　of　a　class　of　constrained　switched　systems　based　on　the　model　predictive　control　approach.　For　a　pre-specified　sequence　of　active　subsystems,　the　optimal　switching　instant　sequence　is　obtained　by　solving　a　finite　horizon　constrained　nonlinear　optimization　problem　and　the　first　switching　instant　is　applied　to　the　system.　Then,　as　an　example,　this　result　is　applied　to　the　traffic　signal　control　of　a　single　intersection.