Whenever you visit Mexico City make sure you use the metro...
It is modern, clean and compared to the continuous gridlock above ground, quite simply the only way to travel.
The trains are built by Bombardier (take note Mr Dave Cameron) and the rectangular (not arched) tunnels actually 'float' in the soft clay of underground DF, so that when there is an earthquake it doesn't collapse, or at least that is the plan and indeed in the 1985 quake it worked!
Best of all it costs 3 pesos (approx 15 English pence!) per journey from anywhere to anywhere (take note Mr Boris) and there is continuous live entertainment that money anywhere else in the world cannot buy, for example people carrying rucksacks with sound systems in them blasting out the latest Shakira/salsa/merengue/ heavy rock cd's which you then have the once in a life time opportunity to purchase for 10 pesos (50 English pence!!!) and if that wasn't enough you can purchase antiseptic plasters, torches, dvd's of childrens tv series, bouncing balls that behave like playdough - just some of this seasons collection.
To top it all, there was even a young man who jumped on with a bag of broken glass that he then prepared as a bed onto which he lay. Clearly (or at least it was to me) he was setting an example for Mr Boris to follow, so I gave him a few pesos for his trouble before he moved on to perform in the next carriage. Granted the blood running down one arm was a little off-putting, but all part of the daily grind I guess.