Washington State’s 18th Amendment: Shaping Transportation Funding for Generations

Washington State’s 18th Amendment: Shaping Transportation Funding for Generations
​

When people hear the “18th Amendment,” they often think of the Prohibition era in U.S. history. However, in Washington State, the 18th Amendment has an entirely different meaning—one that directly affects how we build and maintain roads and highways.
​
Adopted by voters in November 1944, Washington’s 18th Amendment, found in Article 2, Section 40 of the State Constitution, shaped the state’s transportation system for more than 80 years. At its core, the amendment ensures that the money collected from motor fuel taxes and vehicle license fees is used exclusively for highway purposes. This provision has become the cornerstone of Washington’s approach to transportation planning and infrastructure investment.

A Constitutional Guarantee for Road Funding
The 18th amendment mandates that revenues from gas taxes and car and truck license fees go into a dedicated fund. This money can only be used for highway-related expenses, such as building and repairing roads, bridges, and highways; paying for engineering and legal work tied to these projects; installing and maintaining traffic signals and signage; and operating elements of the highway system such as bridges and ferries. Importantly, it cannot be spent on public transit systems, bicycle infrastructure, or pedestrian walkways.
This strict allocation of funds was intended to protect the interests of drivers, ensuring that the money they contribute through taxes and fees is reinvested in the roadways they use. Before 1944, those funds could be diverted for other uses, sparking concern among voters who wanted greater transparency and accountability in how transportation dollars were spent.

Why It Matters Today
The 18th amendment plays a vital role in Washington’s ability to fund long-term transportation projects. Providing a consistent and protected revenue stream allows the state to plan and execute major initiatives, such as freeway expansions and bridge replacements, with greater confidence. The amendment also reinforces fiscal transparency by preventing lawmakers from reallocating highway funds to unrelated programs, a safeguard that helps maintain public trust in government budgeting.
Beyond financial management, the amendment supports the state’s economy by sustaining a reliable network of roads and highways. An efficient transportation infrastructure is critical for moving goods, services, and people throughout Washington. By securing funding for these purposes, the amendment underpins broader economic activities and regional trade.

Impacts on Budgeting and Policy Decisions
The influence of the 18th amendment extends well beyond road construction. Over the past two decades, increases in gas taxes have helped finance landmark transportation projects, such as the I-405 corridor improvements, the new SR 520 floating bridge, and critical repairs to I-5. However, the amendment also creates budgetary challenges. Because its rules only allow spending on highway-related purposes, funding for public transit, ferries, and non-motorized transportation must come from other, more flexible sources such as general sales tax revenue or carbon pricing programs.
This division of transportation funding into “protected” and “unprotected” categories adds complexity to the state’s budget planning. Lawmakers must carefully assess each proposed project to ensure it aligns with the amendment’s legal definition of “highway purposes.” Courts have weighed in on several gray areas, sometimes ruling that park-and-ride facilities or utility relocations related to road projects qualify—and sometimes not—depending on the circumstances.

A Key Piece of Transportation Policy
For legislators, the 18th amendment set clear boundaries on how gas tax revenue can be used. Careful planning and legal review are required to ensure compliance and to avoid misallocations that could trigger legal challenges. More broadly, it shapes the way Washington prioritizes transportation spending and infrastructure development.
While the amendment has provided funding stability and helped build a robust highway system, it also limited the state’s ability to shift focus toward modern transportation needs, such as expanding public transit or preparing for a low-emission future. As Washington faces growing challenges—traffic congestion, climate change, and the shift to electric vehicles—some policymakers and advocates are beginning to question whether the 18th amendment still reflects the state’s transportation priorities.

Washington’s 18th Amendment is more than just a financial rule; it is a foundational element of the state’s transportation strategy. This ensures that funds collected from drivers are reinvested in the roads and highways on which they rely, providing transparency and economic support. However, as transportation needs evolve, the amendment also imposes constraints on innovation and flexibility. The debate over its future is likely to continue, but for now, it remains a guiding force in how Washington builds and maintains its transportation infrastructure.