In the environmental research literature, option value is commonly interpreted as the value of preserving threatened natural resources so that they might be available for use in the future. It has been applied for establishing the value of preserving wildlife habitats,[2] wilderness areas,[3] and water recreation resources.[4] In the transportation research literature, option value is most commonly interpreted as estimated the value that non-users are willing to pay to ensure continued availability of a rail transport facility and its service (as an option that will be available in the future).[5] It is recognized as a type of benefit to be considered in cost benefit evaluation of transportation investment alternatives by the UK Department for Transport[6] and the Scottish Government,[7] and has also been used for assessment of regional rail projects in the Netherlands.[8] In the US, option value is recognized in several transportation benefit-cost analysis guides, including those of the Transportation Research Board's Committee on Transportation Economics,[9] the Transit Cooperative Research Program,[10] and the Victoria Transport Policy Institute.[11]