  We study two perpendicular intersecting flows of pedestrians. The latter are
represented either by moving hard core particles of two types, eastbound
($\symbp$) and northbound ($\symbm$), or by two density fields, $\rhop_t(\brr)$
and $\rhom_t(\brr)$. Each flow takes place on a lattice strip of width $M$ so
that the intersection is an $M\times M$ square. We investigate the spontaneous
formation, observed experimentally and in simulations, of a diagonal pattern of
stripes in which alternatingly one of the two particle types dominates. By a
linear stability analysis of the field equations we show how this pattern
formation comes about. We focus on the observation, reported recently, that the
striped pattern actually consists of chevrons rather than straight lines. We
demonstrate that this `chevron effect' occurs both in particle simulations with
various different update schemes and in field simulations. We quantify the
effect in terms of the chevron angle $\Delta\theta_0$ and determine its
dependency on the parameters governing the boundary conditions.

Statistical Mechanics