Carpooling considered for congestion

The ARTM has been asked by the transport ministry to set up a carpooling system to reduce the congestion inevitably coming when the REM construction and the L-H-Lafontaine tunnel work overlap. But why make this a temporary measure? I know some American cities have permanent carpooling lanes and a culture called slugging has grown up around it. Montreal may be attaining that kind of size and sprawl.