Accenture Assessment Centre - Idea Generation Exercise



I have my Accenture assessment day coming up, and needed some help for the idea generation task.

I got to this stage last year, and the reason for not getting an offer was because my ideas were not original enough. Does anyone have advice on what they would look for?

For example, I read that one person had a case study where the Underground was underfunded and over-crowded, and they had to think of different solutions. What sort of ideas would they look for in this case study???