Compared with many of those posting on transit geek sites I have participated in, and the signal engineers at New York City Transit where I once worked, I’m not an expert in subway and road capacity. But compared with those who have been making an issue of it, well, in the country of the blind the one-eyed man is king, so I’ve elected to provide an overview of what I know in a post. Before getting technical, however, the most important thing about the capacity of the region’s rail transit service is this: there is more room on the tracks than the region will ever be able to use during most of the day; the only capacity problems are during the AM and PM weekday peak periods, and the only severe capacity problems are during the peak hour within those periods. Meanwhile, the streets of Manhattan and some parts of the outer boroughs are congested for much of the day, and in some cases increasingly congested as the day goes on. That is because during the AM rush hour, the capacity of the bridges and tunnels entering Manhattan, and their approaches, limits the number of vehicles on the streets, but as the day goes on more and more are present and trying to move. During peak hour most people are already taking transit, so congestion pricing is more likely to shift drivers to transit during the off peak period, when there is plenty of room to add more riders and, if needed, trains.