Response to Comment on "Fuels for Urban Transit Buses: A Cost-Effectiveness Analysis".

The article responds to comment on fuels for urban transit buses. In response to the cost-effectiveness analysis of alternative propulsion technologies for urban transit buses, researchers noted two points. First, they note that emission controlled diesel (ECD) technology is improving rapidly. Any comparative evaluation of propulsion systems is of course complicated by the "moving target" nature of the technologies, a factor that is relevant to both the ECD and compressed natural gas (CNG) technologies. Second, the wide ranges reported for the number of Quality Adjusted Life Years saved by ECD and CNG as evidence that quantifying in this way is not useful.