I found this sentence in an IELTS book and am questioning whether it is correct:
"It would be a good idea to ban cars from city centres on Sundays, so as to makes cities quieter and cleaner for people to walk around."
No. It should be 'so as to make', not 'makes'.
But if you're curious about the 'so as to make' part in general, in situations like this, 'so as' means something like 'the manner previously mentioned'.