Although we are early in the ST3 program, some observers are already looking forward to extending Link light rail lines into the suburbs and adding more lines in Seattle. The ST3 plan funds several studies of suburban extensions. Current taxes do not support further expansions at the pace of ST3, however. Unless Sound Transit secures another large tax increase, capital spending beyond ST3 will be mostly squeezed out by the costs of managing what has already been built and financing the bonds accumulated in ST3.

The budget for future projects is constrained by Sound Transit’s tax authority. Sound Transit levies nearly all the taxes currently permitted by the Legislature; the only unused authority is a small rental car tax. Any prospect of further authority is hard to forecast. Certainly, it is difficult to imagine today’s Legislature granting more tax authority. Many legislators were unhappy about how the ST3 program far outran the smaller 15-year program they anticipated in 2015, and high car tabs remain unpopular. On the other hand, fifteen years is a long time in politics, and a new generation of legislators in the 2030s may take a sunnier view.

But let’s suppose we are limited by current law, or equivalently that voters resist new taxes. In that scenario, Sound Transit might ask voters in the waning years of the ST3 program to authorize more projects with an extension of current taxes. How much could Sound Transit build with voter approval if they just roll the current law taxes forward indefinitely? Less than you might expect. It turns out that a capital program extended to 2060 would have a run rate perhaps only a third as large as the 2016-2041 program.

Why is this? ST4 will face several constraints that were not present in ST3. Continue reading “Sizing ST4: future rail expansions will be smaller”