Answers About Transportation in New York City, Part 1 Transportation in New York City is universal, mysterious and idiosyncratic - which is why we're here to answer all your questions about it. We've been taking questions from readers about anything that moves in the five boroughs, from yachts and helicopters to defunct subway trains and long-lost rail routes. Here is the first set of responses. We'll keep posting answers throughout the week. When, why, and how, did 30 miles per hour become the default speed limit inside New York City? Posted by David, Stuyvesant Town New York City's streets used to be governed by rules dating to the horse-and-buggy era, which limited the speed of "pleasure cars" to 15 miles per hour within the city limits. While many safety advocates would prefer a return to that figure - and, frankly, it's not often that a car can reach even half that speed in Midtown Manhattan - a proposal to increase the limit to 30 miles per hour was put forth in March of 1936. "Everyone goes beyond the speed limit now," said a city official at the time. If we enforced the old law, we would tie up traffic in the whole city. The proposed higher limits coincided with the introduction of progressive traffic signals, allowing for "express streets on which vehicles will be able to maintain the maximum speed," according to a contemporary report in The New York Times. Still, various reports seem to suggest the city's speed limit fluctuated over the years depending on borough or type of road - until 1964, when, on Oct. 1, the city's speed limit was officially increased to 30 m.p.h. from 25 m.p.h. It was a change made reluctantly, and apparently forced on the city by Albany. Henry Barnes, the traffic commissioner at the time, told newspapers that the change was mandated by a new state law, which forced every municipality to set a minimum limit of 30 m.p.h. Mr. Barnes told The Times that he could circumvent the law only by posting 500,000 signs across the city that specified a lower limit, which would have cost $7.5 million. The result, he said, would have been an "unsightly mess." These days, the city is recording record lows for traffic fatalities. In 1936, the streets appeared to be far more dangerous: The Times reported that 10 people had been killed in a single week that year from automobile accidents. They called that number "encouraging," since 17 people had died in the corresponding week a year prior. On Tuesday, Janette Sadik-Khan, the current transportation commissioner, announced that more city neighborhoods would be adopting a 20 m.p.h. limit. The city plans to install more of these "slow zones" in the future. Michael M. Grynbaum Why does it take so long for subway doors to open at the final stop on the line? Posted by James, New York Why did the M.T.A. recently switch the A trains (with orange/yellow seating) with the C trains (blue seating)? Posted by BRKaplan, Inwood The answer to both questions has to do with air-conditioning. Subway cars often idle for several minutes at their terminal stations before departing on their routes. During this period, the conductor keeps nearly all the doors closed to keep in cool air (or, in winter, to retain heat). It may seem like a pain to squeeze through that open half-door, but the environment will be far more comfortable inside the car than the alternative. With the A and C trains, the M.T.A. is again thinking about passenger comfort. The old steel R32s on the C line are about a half-century old - among the oldest subway cars in operation anywhere in the world. It means that their air-conditioning systems are not quite as powerful as the newer cars on the A line. So starting last summer, about half of the C cars were switched onto the A line as a way to lessen the demands on overtaxed air-conditioning units. The C runs entirely underground in stifling conditions, while the A has a long outdoor run in Queens that provides natural cooling. The cars are expected to return to the C line after Labor Day. Why do the Second Avenue subway and the No. 7 train extension cost so many billions of dollars, while major cities in Europe and Asia can build new subway lines at a much cheaper cost? Posted by Stephen Smith, Villanova, Pa. This is a complex issue that spans many decades" worth of history and politics. But City Room, as you know, is here to tackle the big questions, so we turned to one of the city's leading thinkers on transportation planning: Jeffrey M. Zupan, a senior fellow at the Regional Plan Association. His reply is below: One reason projects cost more in the United States is that we allocate less money per capita for infrastructure. Funding for big projects is often uncertain and is delivered in phases. This forces agencies such as the M.T.A. to stretch out the time frame for major projects, which can lead to increased costs. And transit agencies end up borrowing money to finance projects, saddling them with debt and interest payments for years. We also generally have more layers of government than in Europe or Asia; that allows for citizen input - which is good - but it can make things more complex. Cities such as New York also go to great lengths to minimize disruption from construction - for example, relocating residents or building temporary sheds to mitigate noise and dust at Second Avenue subway sites. But that also costs money. And there are stringent environmental regulations that must be followed, although the Regional Plan Association has proposed ways to reduce the time and money required for that [PDF]. Wages for American workers can be far higher than places like Asia, though this is not necessarily the case in Europe. In the United States, New York has some of the strictest work rules, mandated either by government or by union contract, which can lead to higher labor costs and longer project timelines. Finally, denser residential areas, like Second Avenue in Manhattan, require an immense amount of effort to build around existing infrastructure. There are fewer disruptions, and a smaller budget, for the extension of the No. 7 subway line, which is being built in a mostly nonresidential area on Manhattan's Far West Side. Jeffrey M. Zupan