  The spatio-temporal structure of traffic flow pattern is investigated under
the open boundary condition using the optimal velocity (OV) model. The
parameter region where the uniform solution is convectively unstable is
determined. It is found that a localized perturbation triggers a linearly
unstable oscillatory solution out of the linearly unstable uniform state, and
it is shown that the oscillatory solution is also convectively stabilized. It
is demonstrated that the observed traffic pattern near an on-ramp can be
interpreted as the noise sustained structure in the open flow system.
