Mr. Tim Duggan:

Essentially any time they like, but they would have to convince us the circumstances had changed sufficiently for us to consider undertaking surveys because it is quite a significant piece of work to undertake a survey of a route or a set of routes. Consequently, if an operator requests one, we would have to be reasonably convinced that it is worth doing. A period of six months must have elapsed to conduct a survey. If a survey was conducted, for example, at the end of 2016, we would be fairly reluctant to undertake another one in the first half of 2017, or even in 2017 in total, unless there were very good reasons to do so.