  Bottlenecks occur in a wide range of applications from pedestrian and traffic
flow to mineral and food processing. We examine granular flow across a
bottleneck using particle-based simulations. Contrary to expectations we find
that the flowrate across a bottleneck actually increases if an opti- mized
obstacle is placed before it. The dependency of flowrate on obstacle diameter
is derived using a phenomenological velocity-density relationship that peaks at
a critical density. This relationship is in stark contrast to models of traffic
flow, as the mean velocity does not depend only on density but attains
hysteresis due to interaction of particles with the obstacle.
