[woodruffw]

> You can do that with a bus

Right, at which point it's a cramped, bumpier trolley. It no longer has the main advantage that buses offer, which is being able to alternate their routes based on traffic or blockages.

You can make bigger buses, but they still need to conform to a different set of safety and size standards. Trolleys can make better use of standard lane space (and frequently fit better into standard lanes in older cities, since they can articulate for turns much better).

Laying track does not have to be expensive. Small-to-mid-sized cities in Europe do it cheaply and sustainably; many of the US's cities have streets that are already graded for streetcars and could be replanted without full surveys. I won't claim that it's uniformly cheaper than running a bus network, but that's not the sole factor in our civic construction process -- we also consider quality of life, performance, and appeal.