All told, advantages in life cycle, capacity, and speed mean that a light rail car is functionally equivalent to at least 11 buses for equivalent types of service. Light rail projects always have terrible cost overruns, so the cost of Austin's light rail project will be much higher than expected. In reality, most new LRT systems have been completed on time and within budget. But light rail lines in Austin would be routed entirely on the surface, with little need for expensive civil works. New light rail construction in Salt Lake City, Denver, and East Saint Louis should be used as the measuring stick.
All light rail does is move transit riders from buses into trains.
All rail riders are taken from buses, not cars. While many light rail riders do indeed come from buses, many others are attracted to light rail from cars. And, while anti-transit zealots promote the notion that only new riders attracted from cars are worth counting, bus riders who are diverted to the new LRT service are also major beneficiaries. Light rail will carry such an insignificant portion of urban travel that it won't have any impact on traffic congestion or air pollution. While no single light rail line will miraculously make congestion and pollution utterly vanish, statistics do suggest an impact.