In the end, out of the three questions we have to choose, we chose:
How do we prevent traffic accidents?
We chose this because we can think of more ideas for it rather than public transport of saving energy. We don't have the sufficient knowledge to solve the problem of limited energy. We also aren't able to find ideas for improving the efficiency of public transport as Singapore and many countries already have solutions to them.
We find this more important as traffic accidents involve lives, which is significantly more important than efficiency of public transport, while saving energy is out of our hands.