The grassland area of freeway rights-of-way in Kentucky was estimated to determine its potential to produce switchgrass (Panicum virgatum L.) for bioenergy feedstock. Kentucky's freeways include 9.2×10³ ha of mowed grassland within their rights-of-way. This area could produce approximately 64×10³ t/yr of switchgrass, sufficient to make 21×10⁶ L of cellulosic ethanol, or generate 64 GWh of electricity annually. Switchgrass grown on freeway rights-of-way could offset about 0.5% of fossil fuel currently used on Kentucky freeways if converted to ethanol, or 0.8% if converted to electricity for vehicle propulsion. Future changes in vehicle efficiency and traffic volume will have much greater impact on the volume of fossil fuel used on Kentucky freeways than conversion of freeway-grown switchgrass to alternative fuel. Kentucky's state government's projection of a 42% increase in traffic volume by 2025 contrasts with this study's projection of 28% decline derived from extrapolation of linear trends observed since 1983. If such a decline is realized in combination with federally mandated vehicle efficiency improvements then freeway-grown switchgrass used for electric vehicle propulsion could offset up to 2% of freeway fossil fuel use in Kentucky by 2025. The contrast between the implications of these estimates reflects considerable uncertainty, but emphasize the importance of conservation in conjunction with alternative fuel production.