In the optimal velocity model with a time lag, we show that there appear mu
ltiple exact solutions in some ranges of car density, describing a metastab
le uniform flow, a metastable congested flow, and an unstable congested flo
w. This establishes the presence of subcritical Hopf bifurcations. Our anal
ytical results have implications for continuum traffic flow, such as hyster
esis phenomena associated with discontinuous transitions between uniform an
d congested flow.