  Improving road safety is hugely important with the number of deaths on the
world's roads remaining unacceptably high; an estimated 1.35 million people die
each year as a result of road traffic collisions (WHO, 2020). Current practice
for treating collision hotspots is almost always reactive: once a threshold
level of collisions has been overtopped during some pre-determined observation
period, treatment is applied (e.g. road safety cameras). Traffic collisions are
rare, so prolonged observation periods are necessary. However, traffic
conflicts are more frequent and are a margin of the social cost; hence, traffic
conflict before/after studies can be conducted over shorter time periods. We
investigate the effect of implementing the leading pedestrian interval (LPI)
treatment (Van Houten et al. 2000) at signalised intersections as a safety
intervention in a city in north America. Pedestrian-vehicle traffic conflict
data were collected from treatment and control sites during the before and
after periods. We implement a before/after study on post-encroachment times
(PETs) where small PET values denote a near-miss. Hence, extreme value theory
is employed to model extremes of our PET processes, with adjustments to the
usual modelling framework to account for temporal dependence and treatment
effects.
