Boston is the most congested city in the U.S.

Much of its population of more than 450,000 is concentrated in a one-square mile area downtown. Some 8,400 horses power its streetcars. There are more than 70 different lines. Some are color coded to denote various routes (e.g., green-Roxbury; purple-Dorchester; scarlet-South Boston; pale blue-Brookline; brown-Brighton; maroon-Somerville & Charlestown. There are even plaid and chartreuse lines.) In a one-hour period, 183 streetcars cross in one direction and 73 streetcars in the other at the intersection of Tremont Street and Boylston Street,