  We present a microscopic driving algorithm that prescribes the acceleration
using three parameters: the distance to the leading vehicle, to the next
traffic light and to the nearest stopping point when the next traffic light is
in the red phase. We apply this algorithm to construct decision trees that
enable two driving behaviors: aggressive and careful. The focus of this study
is to analyze the amount of aggressive drivers that are needed in order to
generate a traffic gridlock in a portion of a city with signalized
intersections. At rush hour, aggressive drivers will enter the intersection
regardless if they have enough time or space to clear it. When their traffic
light changes they block other drivers, thus providing the conditions for a
gridlock to develop. We find that gridlocks emerge even with very few
aggressive drivers present. These results support the idea of promoting good
driving behavior to avoid heavy congestion during rush hours.
