It's the people. Mainly that there's too many of them. Although the quality often leaves much to be desired as well. I remember once reading that the "far-sighted" metro planners made the platforms twice as long as the original trains because they knew that one day there would be many more people using the system. Well, it was a shame they weren't a little more far-sighted because the Moscow metro has reached capacity. As an example, centre bound trains on the south green line in the mornings are almost impossible to board from Kantemirovskaya onwards, even though they come as often as every 30 seconds. You literally have to put your shoulder into the people and push to force your way on. The 'people's palaces' are now no better than overcrowded farmyards running stinking, stuffy cattle trains.

And the question is, where do they go from here? The frequency definitely can't be increased. The only option would be to extend the platforms and who knows if that would even be possible with many of the existing stations or how long it would take to do it. How would the system have coped if Moscow had won the Olympics? This post might upset a few travelers who have marveled at the pretty decorations and been surprised by the efficiency of the system. But ride the metro every day and then see how wonderful you think the little statues at Ploshchad Revolutsii are.