The quality of the sustainability plans of 11 state departments of transportation (DOTs) is systematically assessed with a content analysis methodology. Analysis reveals that state DOTs that have created a sustainability plan are also likely to have developed a policy framework aligned with the principles of sustainable transportation within their plan. The quality of a sustainability plan is driven by the strength of its policy framework, including plan visions, goals, policies, strategies, and performance measures. External drivers of plan quality include the presence of a prescriptive state sustainability mandate, external funding for plan development, and the involvement of a policy entrepreneur in plan development. Prescriptive mandates and external funding bolster the quality of the plan development process and the degree to which the plan is integrated with existing policies and practices of the DOT and other agencies. A policy entrepreneur's involvement in plan development strengthens the policy framework and helps unify plan content toward a consistent vision. In addition to conclusions relating to the development of transportation sustainability plans, this study illustrates the value of systematic and objective content analyses in assessing the quality of transportation planning documents.