Toward a Better State Climate Action Plan

Abstract

A major body of transportation greenhouse gas (GHG) reduction strategies is contained in state-level climate action plans (CAPs). There has been some concern among major stakeholder groups that CAPs are not rigorously developed documents and that the reductions estimated in CAPs are unrealistic given real constraints on funding and implementation authority. This paper analyzes a subset of 84 strategies in nine states’ CAPs to determine how reliable reduction estimates are and where significant sources of uncertainty arise. Measures from these CAPs are evaluated according to requirements for enactment, external factors that play a role in implementation, quantification methods, and variables used in the quantification. For enactment of strategies, nearly all of the transportation GHG reductions estimated in state CAPs would require new state legislation or state agency rulemaking. Half of the reductions would require major new funding. For implementation factors, one-third of state CAP GHG reductions relies heavily on assumptions about the future price of transportation. A relatively small portion (10%) of the estimated GHG reductions depends on changes in land use. Some of the greatest uncertainty stems from strategies that are quantified with goals rather than empirical data and are not supported by a feasibility study. The authors judge that if state CAP transportation strategies are enacted as stated, roughly one-third of the estimated reductions in GHG emissions is highly uncertain. As states develop and revise CAPs in the future, they can focus on developing and quantifying strategies in a way that increases the likelihood that strategies will achieve at least the reductions estimated.