After the great London fire of 1666 destroyed 80% of that city, Sir Christopher Wren was given the monumental task of rebuilding. His influence can be seen everywhere, with some of the most beautiful and lasting buildings, including St. Paul’s Cathedral standing as a lasting tribute to his great works. Despite this, one thing Sir Christopher did not achieve was better transportation. Because many building basements survived, legal disputes arose over land ownership and the plan for a grid city with wide avenues was abandoned. The city was rebuilt along the lines of its existing street plan but with modern additions like a sewer system. Thus even today London consists primarily of many small, congested streets and small, congested sidewalks.

Paris, in contrast, was rebuilt under the direction of Napoleon by razing entire city blocks in order to create wide, modern boulevards and thoroughfares, dozens of bridges over the Seine, and massive parkways and sidewalks that, one would think, would serve to make the city a clean and pleasurable place in which to travel. Remarkably, the amount of congestion in Paris is similar to that of London. The main streets are massive, with a dozen lanes, their sidewalks wide enough to let two dozen people march side-by-side. Areas outside monuments and landmarks contain huge amounts of open space. Paris is simultaneously a dense urban center and a comfortable, spread-out, well-designed transportation conduit.

So why are the Paris streets and walkways just as packed as those of London? Why are the bridges just as crowded? I think that people have a remarkable ability to expand to eat up all available space. If two dozen people can walk side-by-side along the sidewalk, then three dozen will try to, jostling and passing and bumping and getting frustrated. Had London more room and the same number of buildings, shops, restaurants, and attractions, more people would come. In California every time a huge new road works project is finished and new freeway lanes come online, they are instantly filled and soon enough we have the same traffic jams. It isn’t going to ever end as long as resources and people are plentiful.

One of the best things about London, Paris, and other dense urban centers that were forward-thinking is that there is plenty of public transportation in the form of trains, subways, and busses. These transportation systems, of course, have the remarkable virtue of becoming *faster* the more they are used. Think about it: the more people you put on a train, the more cars they will add, the more trains they will put in service, the more people will get to their destinations more quickly. Up to a (very high) saturation point, trains and subways and monorails can continue to be expanded in a way that makes them *more* efficient, not less. For busses this is true to a lesser extent. The Paris Metro trains I’ve ridded have all been crowded. Same goes for their commuter rail. Same goes for the London Underground. These services *do* start to reach their saturation point, but the sidewalks and the roads serve as the necessary bottleneck that keeps all the other services functioning at their peak efficiency.