THE CHICKENS, BRONCOS, Mustangs, and Beetles all came home to roost for King County last week. In a decision that could throw hundreds of new housing developments into doubt, Hearing Examiner Stafford Smith ruled against the county government in a closely watched lawsuit over traffic.

The case involved the appeal of a “concurrency” certificate given to an East Sammamish Plateau development called the Greens at Beaver Crest. To certify concurrency, King County relies on a computer forecasting model that attempts to predict how many car trips a new housing development will generate, at what time of the day, going where, and on what roads. With the help of a Bellevue traffic engineer, Plateau resident Scott Hamilton argued that the county’s forecasting methods were full of erroneous data and dubious assumptions—all of which serve to underestimate the traffic impact of new housing projects and thereby ease their way to approval.

Hearing Examiner Smith agreed, saying that the county’s methods “systematically and consistently produce artificially low [traffic scores].” He ordered that the Greens be subject to an onerous environmental impact statement and that the county rerun its concurrency test after correcting its numerous errors.

Immediately after it was issued last Friday, County Executive Ron Sims promised “a vigorous appeal” of several parts of the decision. In a later interview, Sims’ public-policy chief Ethan Raup took a softer stand, saying that the county will “embrace some of [Smith’s] other recommendations.”

As of this past Monday, county officials were still trying to sort through the highly complex, 57-page ruling. It is unclear whether the county will be able to continue accepting new housing applications now that its initial tool for evaluating those permits has been thrown out by the court. Even more troubling from the developers’ point of view is the threat posed by this decision to the thousands of proposed homes that have already received a concurrency certificate but have not yet made it through the rest of the county’s approval gauntlet. Those projects could well be “exposed to the ruling,” according to Raup.

ALTHOUGH SMITH’S CRITICISM of the county’s traffic forecasting model received the most attention in recent days, Smith demanded an equally important—and, from the developers’ point of view, alarming—change to the county’s growth practices. Smith ruled that the county has been wrong in ignoring a development’s impact on traffic in nearby cities. Most specifically, Smith ruled that, in the case of the Greens, the county must take into account the traffic impact on some key suburban intersections that are located in neighboring Redmond and Issaquah, rather than look only at intersections in unincorporated land. This is an important ruling to the cities, who have become increasingly uneasy with the county’s go-go development policies.

For developers, the Greens ruling could be a nightmare. The most desirable, buildable suburban land is in unincorporated areas, but traffic is often funneled to a few congested choke points in nearby cities. Smith’s ruling could help grind new development to a halt. Anticipating the decision, Sims—who will decide in two weeks which parts of the ruling to appeal—has already moved to subvert it. He has proposed a change in the county code that, while tightening up some traffic standards, would also explicitly remove non-county intersections from the concurrency test.

In an interesting twist, the case—to be heard in Superior Court—will pit the county against itself. The Department of Transportation is part of the executive branch, and the hearing examiner reports to the County Council. Both sides will be represented by attorneys from the King County prosecutor’s office.

The Greens case seems to have shaken the faith of some county officials in a growth-management system that they have, until now, vigorously defended. The evidence presented in Greens made it painfully clear that responsibility for the county’s growth decisions has been removed from elected officials who can be held accountable and lodged instead in a computer program understood only by a closed circle of county engineers. Approval of the Greens ultimately relied not on the public interest but on arcane, and falsely exact, forecasts—such as the precise percentage of car trips that would make a pm/peak hour trip in a northerly versus a southerly direction.

In his statement last Friday, Sims declared, “We believe that our transportation model is a reasonable tool for implementing growth management.” But Raup says there is now talk of finding another way. “We’re working directly with the council staff to look at other ways to make these growth-metering decisions, so they’re not made on the basis of the model,” he says. “That’s not the best tool.”