There hasnt been a terrorist attack on the London transport network since 2005 so by looking at a journey to explosion ratio, it would appear we're fairly safe. However, you'd be crazy if you didn't think about it every now and again. After all, the UK threat level for international terrorism has bounced between substantial, severe and critical ever since 2005. Bear in mind that severe means that a terrorist threat is highly likely and when and where are they probably going to attack if it happens again? Probably exactly the same time and place as last time. On a tube and/or bus in London during rush hour. It's a sad, kind of terrifying fact that we just have to try not to think about.