On Thursday there was a tube strike in London. This meant I had to take the overground train to work. I got to the station early knowing there would be a lot of people taking the same train. It was hot and I was dreading the journey in to work. I managed to get on the first train that came by. In front of me there was a young blonde woman (early 20s), who had an amazing body and was wearing denim mini shorts and a white tank top.  I got on to the train with her...there was very little space to stand. I was stood next to the door which just about closed. I found myself standing right up against her with her back towards me. As the train set off she looked back and gave me a smile. I thought nothing much of it at the time. As the journey continued I found that this girl was backing into me....I looked down and saw her amazing ass grind me up and down slowly around my cock area. I moved forward in to her slightly so that she could feel my now rock hard cock up against her ass. She looked back sideways with a smirk....she liked the fact that she turning me on.  She kept grinding her ass in to me slowly up and down against my body. Her ass looked so good...so fuckable. I looked around to see if anyone noticed but there were all in their own world. I was rock hard and if I had my flies unzipped my cock would literally be inside her ass. The train came to a sudden halt which made me lean in to her more...and to keep my balance my hands groped her ass so that I didn't fall on top of her. She didn't mind at all as she looked back with a smile. The train stopped at it's last stop where everyone got off. When we got off we just smiled at each other and walked our seperate ways.