"Modern urban planning literature is filled with references to grid street patterns and their alleged superiority to the cul de sac--a loop or dead-end street pattern typical of modern suburban developments. The new urbanists claim grids are needed to reduce traffic congestion and smooth the flow of traffic.
But advocates of grid street patterns contradict themselves. They claim local grid streets are needed to smooth traffic by easing the load on higher-capacity streets ... but then they also propose traffic calming measures, such as speed bumps and roundabouts, to make traffic move more slowly on the local streets. Such measures nullify any advantage local grids might be argued to have over cul de sacs."
Thanks to Brenda Meyer