Back in the day, they used to build elevated railroads in Boston

[sup]      Widen the street to accommodate twelve lanes of traffic?[/sup]

Underground construction was still quite primitive. The Tremont Street Subway wasn't (and still isn't) a real rapid-transit line; it was only built so that trolleys could avoid the worst congestion in the center of town.

Twenty years later when the Red Line was constructed, mechanized equipment made it practical to build straight tunnels for much longer distances.

Of course, an underground subway would have been better, but in 1899, an elevated rapid-transit line was much better than doing nothing at all.

Visiting in Chicago this summer (after a too-long hiatus), I have to say that I think Els get too much of a bad rap. Chicago's "L" is pretty nice for the most part, and you get such a great view too.

One major difference between Chicago's system compared to Boston's old El and NY's though is the fact that the Chicago "L" largely runs along alleyways behind buildings (outside of the central Loop area where it really does cover streets). The "L" doesn't really run for long distances above main streets in the outer neighborhoods. That probably helps, and wasn't really an option here.