Dedicated vehicles are designed to run strictly on natural gas. Dedicated Original Equipment Manufacturer (OEM) vehicles are built from the manufacturer to run only on natural gas while dedicated conversion vehicles have the gasoline or diesel fuel system removed or de-activated. Bi-fuel vehicles can run on either natural gas or gasoline. Dedicated vehicles generally run slightly more efficiently when running on natural gas than do bi-fuel vehicles because the engines are adjusted to run solely on natural gas.
Dedicated vehicles are limited by the range of the particular vehicle and work well for local fleets that return to a fueling site regularly or commuter vehicles that do not require an extended range. Bi-fuel vehicles work well for vehicles that occasionally need to travel beyond the range of fueling stations.
Conversion costs for dedicated or bi-fuel vehicles are typically about the same. However, bi-fuel vehicles did not qualify for the previously available Federal tax credits. There is pending legislation before Congress that could reinstate those incentives and possibly extend them to bi-fuel vehicles as well. Details of the currently available vehicle incentives are at: http://www.ngvamerica.org/incentives/federalTax.html.