I have heard via a site visitor that there are two new OSIs in place for the period of the Olympics and Paralympics. The first one is between Aldgate and Aldgate East and works as long as you touch back in within 20 minutes, either way round. The second one is between London Bridge NR and Monument allowing 30 minutes to walk across the river. In both cases the OSIs are active between July 22nd and August 12th, and again between August 29th and September 9th.