This short but fascinating article in The Atlantic explains why pedestrians in larger cities walk faster:
"Levine measured three "pace of life" variables — walking speed, work speed, and clock accuracy — though for the purposes of this post, in keeping with the previous literature, we'll focus on the first. The top ten cities for walking speed, according to Levine, were as follows: Dublin, Amsterdam, Bern/Zurich, London, Frankfurt, New York, Tokyo, Paris, Nairobi, and Rome.
With the exception of Nairobi — insert joke here about Kenyans crushing everyone at the New York City Marathon — the fastest walking cities were from wealthy nations. The statistical analysis confirmed this general perception: two of the three strongest social predictors of walking speed were a country's G.D.P. and its purchasing power parity (the other was its individualism). Indeed, when Levine considered all his "pace of life" metrics, he found that pace of life was swifter in "economically productive countries" like Western Europe and Japan than in undeveloped countries."