The laws of the physical universe are simple. Every action has an equal and opposition reaction. Matter is neither created nor destroyed. And light rail projects always, always cost much more than politicians promise.

Metro Seattle's 8.5-mile Lynnwood Link light rail extension is no exception to this rule. Sound Transit disclosed the already exorbitant $2.4 billion the project is six months behind schedule and will cost an additional $500 million.

It is just the latest in a long series of delays and cost increases added to the project, and it casts doubt on the ability of Sound Transit to bring in the Sound Transit 3 initiative approved by voters in November 2016 at anywhere near its staggering $54 billion estimated cost.

Sound Transit CEO Peter Rogoff didn't let a little bad news get him down. "It's certainly a disappointment to everyone," Rogoff told the Seattle Times. But he assured the paper cost overruns would not prevent Sound Transit from expanding the Lynnwood line, first approved by voters in 2008, deep into the Seattle suburbs.

Mariya Frost, a transportation policy analyst with the Washington Policy Center, wasn't nearly as chipper.

"Who at Sound Transit got fired for this," Frost responded to a Reason inquiry in an email. "How can the public hold Sound Transit officials accountable for their consistent pattern of broken promises?"

According to a 2013 Federal Transit Administration document, Sound Transit initially projected the Lynnwood line to cost as little as $1.2 billion. In April 2015, a final version of the project's Environmental Impact Statement said Sound Transit's "preferred alternative" would cost somewhere in the $1.5-1.7 billion range.

By November 2016—just as voters were approving the $54 billion ST3 plan—Federal Transportation Administration ratings of the project assumed it would cost $2.3 billion.

Now, according to staff reports released last Thursday, the Lynnwood line will cost $2.9 billion, and will begin operations in mid-2024, not December 2023, as first promised.

The cost increases include $101 million for the escalated price of the real estate needed for the project; $140 to $190 million in added construction costs; and another $150 to $190 million to expand the original project, $32 million of that for landscaping and tree planting.

Sound Transit built its reputation, such as it is, on broken promises. The agency won approval in 1996 for completing a 21-mile light rail network by 2006 for $2.3 billion. The agency completed the network a decade after that for $5.3 billion.

To handle this latest round of miscalculations, Sound Transit announced it will be issuing "a modest amount of additional debt", the final sum of which will be known to taxpayers sometime in the fourth quarter of its fiscal year after the agency has a more complete idea of the different sources for the money.

One likely source is revenue from increased taxes and car registration fees voters approved for the ST3 initiative. Those revenues are supposed to buy 62 miles of new light rail lines, but the ballot initiative was written in such a way as to allow taxes and fees to be spent on the Lynnwood line.

Witting or not, voters have seen their car fees triple, and will be paying out $300 to 400 per household in new taxes. Popular support for ST3 has since plummeted, and the Washington State Senate is now conducting an investigation into how Sound Transit assesses its fees.

Funneling fees from a new light rail project into older, overbudget, light rail projects for which they've been paying taxes for almost a decade is a questionable way to win public support for an expansion that is unlikely to come it at its projected $54 billion.

"If Sound Transit officials can't project what they need year to year," Frost says, "then how can the public trust them to be on time and on budget over the next 25 years?"