  We propose a cellular automata model for vehicular traffic in cities by
combining (and appropriately modifying) ideas borrowed from the
Biham-Middleton-Levine (BML) model of city traffic and the Nagel-Schreckenberg
(NS) model of highway traffic. We demonstrate a phase transition from the
"free-flowing" dynamical phase to the completely "jammed" phase at a vehicle
density which depends on the time periods of the synchronized signals and the
separation between them. The intrinsic stochasticity of the dynamics, which
triggers the onset of jamming, is similar to that in the NS model, while the
phenomenon of complete jamming through self-organization as well as the final
jammed configurations are similar to those in the BML model. Using our new
model, we have made an investigation of the time-dependence of the average
speeds of the cars in the "free-flowing" phase as well as the dependence of
flux and jamming on the time period of the signals.
