Most of the recent research on factors affecting vehicle speeds is summarized in http://onlinepubs.trb.org/onlinepubs/circulars/ec151.pdf http://onlinepubs.trb.

Most of the recent research on factors affecting vehicle speeds is summarized in http://onlinepubs.trb.org/onlinepubs/circulars/ec151.pdf http://onlinepubs.trb.org/onlinepubs/circulars/ec151.pdf In it, Dimauita et al credit every foot of lane width with a 2 mph increase in vehicle speeds, and Wang et al credit each additional lane with a 6.5 mph increase.