For 63 years, the federal Highway Trust Fund has supported the construction and maintenance of our nation’s highways and transit systems. But it’s going broke (again). Congress has failed to ensure the fund’s long-term sustainability, opting instead to pursue a handful of accounting gimmicks and one-time measures to plug gaps between the fund’s declining revenues and ever-higher infrastructure needs. As a result, the trust fund faces a cash flow crisis and will run dry between 2021 and 2022.

On both sides of the balance sheet, the Highway Trust Fund faces a series of both existing and emerging challenges that threaten the fund’s sustainability. As Congress once again gears up to reauthorize trust-fund-supported programs, it must face the unavoidable truth that without structural reform, the future of the fund is bleak.

The problems with the trust fund stem from two underlying flaws in how the money comes in, and the growing challenges of how (and how much) needs to be spent.

Highway Trust Fund implications: Core transportation infrastructure assets have been neglected for decades and will now require vast sums to be restored to a state of good condition. Yet this comes at a time when our roads are more trafficked than ever, necessitating additional investments in new capacity in our highway and transit systems. This puts new pressure on policymakers to increase outlays from the Highway Trust Fund or face the negative consequences of underinvestment—increased congestion, jeopardized safety, and diminished economic potential.

Outlay Problem #2: Damages from Climate Change

While the political debates on climate change continue, our nation’s highways are already dealing with increased extreme weather and disasters. Across the country, there is roughly $3.4 trillion worth of highways, and from 2011 to 2018, damages from disasters required them to receive $6.4 billion in emergency relief appropriations (on top of the existing $100 million annually allotted for emergency repairs). As climate change fuels more frequent and more severe disasters, both inland and coastal highway assets are at risk of further damage. Without reductions to emissions, the EPA estimates that by the end of the century, 190,000 inland bridges across the country will be structurally vulnerable as a result of climate change.

While direct damage from a storm is typically covered by supplemental funding and doesn’t necessarily threaten the solvency of the trust fund, climate change is also increasingly inflicting small-scale damage that increases the need for routine highway maintenance.

Highway Trust Fund implications: As our climate changes, more frequent disasters and extreme weather events will inevitably damage highways, increasing repair and maintenance costs. Avoiding increased risks and mitigating damage requires using more resilient materials and designs, but those inevitably come with higher price tags. These mounting costs will further increase demand on the Highway Trust Fund amid declining revenues.

Shifting Transportation Priorities

As vehicle miles have increased dramatically in recent years without a significant change to our transportation systems, congestion has skyrocketed. Traditionally, policymakers have looked to reduce congestion by expanding highways, but recently researchers have discovered that those projects are not achieving the desired effect. Instead, the phenomenon of “induced demand” can occur—where, as more lanes are added to a highway, more people are encouraged to drive along that route, and, in the end, congestion remains the same. New York City has taken a new approach. Instead of building more lanes, the city plans to implement a congestion pricing model that directly increases the cost of driving in congested areas. In addition to the hopes of reducing congestion, a significant portion of proceeds will directly support the infrastructure of transit alternatives.

Similarly, while driving remains fundamental to the way of life for a most Americans, a growing number of cities and states are holistically examining past land use decisions as they plan future projects. Along with setting emission and congestion reduction goals, the series of health risks associated with living near highways are being taken into consideration. In an overall effort to reduce or eliminate the day-to-day necessity of driving a car, some urban centers are going so far as to tear down large segments of highways and replace them with better infrastructure for pedestrians, bicycles, and transit systems.

Highway Trust Fund Implications: If efforts to reduce driving are successful, it will be directly reflected by a decline in the revenue collected by the gas tax (barring the introduction of an equivalent transit or bicycle tire tax). While today only a handful of cities and states are prioritizing infrastructure projects and policies that directly aim to reduce driving, these developments could represent an early warning sign that views on the role of highways are shifting. If so, the Highway Trust Fund’s entire structure and mission would need to be reformed in order to support the divergence in transportation needs of urban and rural communities.

Reform is Needed

The economy and transportation networks of the United States are designed around the Interstate Highway System. The Highway Trust Fund that supports this network is in a troubled state, built on the back of a fuel tax that has remained stagnated and one that repeatedly fails to engender political support. Meanwhile, America’s highways are both being used more today, and are more at risk of disaster damage, than at any point in history. As such the need for maintenance and repair has reached similar unprecedented levels.

Simply raising the gas tax would go a long way in addressing the trust fund’s balance sheet problems. However, without any further reforms, the future of the fund looks bleak. The current structure and mission of the trust fund are not designed to withstand several of the emerging technological and policy trends, from the potential shift to electric vehicles, to the impetus to radical transformations as necessitated by climate change.

A larger conversation around the funding and function of the Highway Trust Fund will be required for the program to both stay relevant and to be a part of the solution rather than part of the problem.