  We investigate the dynamics of the asymmetric exclusion process at a
junction. When two input roads are initially fully occupied and a single output
road is initially empty, the ensuing rarefaction wave has a rich spatial
structure. The density profile also changes dramatically as the initial
densities are varied. Related phenomenology arises when one road feeds into
two. Finally, we determine the phase diagram of the open system, where
particles are fed into two roads at rate $\alpha$ for each road, the two roads
merge into one, and particles are extracted from the single output road at rate
$\beta$.
