1) Like the others are saying, you need to find a (better) designer
2) Playing the game seems to be a massive time sink. I could never spend that much time on a game, regardless of how good it is. And I don't think it's just me, pretty much nobody with a job could spend a few minutes every half hour to run their taxi company. Which ties into..
3) Too much micro management. This is mostly a personal preference, but I'd get tired of micro managing my cabs pretty soon.
Things that would make it easier for me to play:
a) Make it possible to play in a rewarding and competitive way spending no more than a quarter to half an hour per day.
b) Less micro management, but that should be a requirement to achieve a) anyway.
I can see the Challenge thing as a mini-game, maybe it could make it on its own as a game widget. Maybe make a Wordpress et al widget that doubles as a game and as an ad for the "big" game?
You have an interesting idea, looking forward to see how it evolves!