Macadamia

It would, but conductors keep costing you money. The question is will the ticket machines cost more than conductors? In most cities, they don't, which is why the complicated CTA and the even more complicated MTA have gone to ticket machines and cards.

The ideal is the travel card, which when travelling in NYC or Chicago, I love. You get this magic piece of plastic, swipe in through, get on, go. Works on the trains and busses. You can either get day cards, multi-day cards, or "pay as you go" cards, with a given amount of value on them, and it deducts the fares as it goes (and, in Chicago at least, displays how much is left -- another usability win.) The CTA system is pretty good about human interface, compared to the London Transport system. The again, the LT system is a paragon of virtue compared to the MTA machines.

This was one of the things I noticed when I moved back to Dublin from Brussels: the amount of time spent stopped at bus stops while people bought tickets and the driver dispensed change. In Brussels, hardly anyone bought a ticket from the driver. You could buy pre-paid 5- and 10-journey tickets at substantial discounts from newsagents and ticket desks and when a bus came, you could get on through any door (the newer buses had three sets: front, middle and back) and there was a ticket reader at each door.
They've since improved things slightly in Dublin. You drop the exact fare into a slot and you are given a ticket. No cash change. (You get a change ticket which can only be redeemed from the Dublin Bus central office in O'Connell Street)

Hear, hear! I'd *love* to see more RouteMaster style buses. Quicker, and you feel safer if there's a conductor about, too.