On the northern edge of Jamaica Plain (east of Brookline in Boston proper), there's a pretty stark example of Brookline's accumulated advantages. On the Boston side of the pond that separates the two, there's Jamaica Way. It's a four lane road with few pedestrian crossings, and drivers regularly going way over the 25mph speed limit. The multi family housing on the Boston side is significantly cheaper and denser as well. It too has a trolley (the E branch of the Green Line), but unlike the Brookline side, the trolley on the Boston side isn't grade separated, so it's quite slow. It also typically runs older rolling stock.