Last week we looked at Urban regeneration and some of the consequences of this, one of which was the relocation of people from urban to suburban areas to to largely allow them a better standard of living. Because housing is cheaper in the suburbs so they have more disposable income but they have to commute and commuters need rapid transport to get them from A to B. So subway construction is wrong with brooming in some parts of the world. It's clearly being seen as the answer to the type of migration that I just mentioned. It often gets huge public support because when you have subways going to help you have a better lifestyle then what's that argue about. Well, quite a lot actually. In order to go ahead with the major project of this kind, you need to be absolutely sure set the ground and more to the point What Lies beneath the ground can support underground transport and to address questions like that engineers have to be really experienced to really knowledgeable about the local area. Water levels land formation and so one and those key issues or what I want to focus on today. Passengers don't think about construction. They trust other better qualified people to do it for them and governments have to choose these people very carefully.