  Urban traffic congestion is a chronic problem faced by many cities in the US
and worldwide. It results in inefficient infrastructure use as well as
increased vehicle fuel consumption and emission levels. Congestion is
intertwined with delay, as road users waste precious hours on the road, which
in turn reduces productivity. Researchers have developed, and continue to
develop, tools and systems to alleviate this problem. Network perimeter control
is one such tool that has been studied extensively. It attempts to control the
flow of vehicles entering a protected area to ensure that the congested regime
predetermined by the Network Fundamental Diagram (NFD) is not reached. In this
paper, an approach derived from sliding mode control theory is presented. Its
main advantages over proportional-integral controllers include (1) minimal
tuning, (2) no linearization of the governing equations, (3) no assumptions
with regard to the shape of the NFD, and (4) ability to handle various demand
profiles without the need to retune the controller. A sliding mode controller
was implemented and tested on a congested grid network. The results show that
the proposed controller produces network-wide delay savings and disperses
congestion effectively.
