Caro’s highway planning

Robert A Caro’s famous 1300 page book “The Power Broker” remains one of the great weapons in the war against roads and the automobile. It is an extremely readable tale of the career of Robert Moses and of the great road and bridge sagas that he led in New York between 1924 and 1968. The book is a sustained vilification of Moses but it is so encyclopedic in its scope, and so well written, it continues to sell well 26 years after it was first published.

And its simpleminded treatment of the roads/transit issue probably continues to influence New Yorkers. Caro ridicules roadbuilding that Robert Moses promoted on Long Island on the grounds that an extra 90k drivers commuting from Nassau, Suffolk and Queens needed to be catered to, and he says the capacity of an expressway lane, under optimum conditions is only 1,500 cars/hour, so sixty lanes of new highway would be needed just to keep up with expected growth. (p943) Cars have improved and an expressway lane can now carry 2,400 veh/hr. Moreover the extra commuters won’t all want to travel in the same single hour. The peak will be spread over 2 to 3 hours, so an extra lane might carry 2.5 x 2,400 or 6k veh vs the 1.5k Caro mentions. Further, some carry passengers so that the average vehicle carries about 1.5 people boosting that to 9k people/lane. Another factor is that in a long highway, such as the Long Island Exwy being discussed by Caro, many trips are local trips. A minority of trips are the length of the highway, so an extra lane built the length of the highway will cater to trips that are a multiple of the point flow capability.

Because so many trips are on-and-off trips that only use a part of the highway - average commutes are 10mi vs the 50mi length of the LIE - it is not unreasonable to think that over the length of the roadway an average of at least three separate trips may be catered to. We’ve now got (3x9k) to 27k commuters/lane and 3 to 4 lanes (90/27) required versus the implied awesome, impossible, ridiculous, stupid, absurd 60 extra lanes (90/1.5) of Caro’s scaremongering calculations.

Moses had serious flaws. He was no doubt a huge egoist, and apparently authoritarian. He was deeply prejudiced against buses, and tunnels. But his critics like Caro have their own agenda and play fast and loose with data in their vilification of the man and his works.