“To you, it’s a traffic jam. To state and city lawmakers, it’s concurrency management, an arcane-sounding concept with concrete applications – literally.The concept, articulated in the state Growth Management Act, is that transportation facilities must keep pace with population growth to prevent congestion from reaching unacceptable levels.What the law does not dictate, though, is what level of congestion is acceptable. That decision is left to comprehensive planners. And the Bainbridge Island answer may come as a surprise, particularly for downtown Winslow.The comprehensive plan accepts near-gridlock conditions, city engineer Jeff Jensen said, because that was considered better than the alternatives of widening roads or building new ones.The city council tonight will begin considering a concurrency management ordinance for the island.It will require any builder whose project will generate more than 50 trips per day to submit a traffic study showing that the additional traffic won’t reduce the so-called Level of Service below that called for in the comprehensive plan.The central concept – Level of Service, or LOS – is a measure of street capacity. It is expressed as a letter grade from A to F. An A level means there will be essentially no interference from other cars. An F level means a road is taxed beyond its capacity.The Winslow Master Plan accepts an LOS grade of E for the city core, meaning that the streets will be used at 100 percent of capacity.At intersections, the LOS is measured by length of wait. The cutoff between an E and F level is a one-minute wait. The critical qualifier, though, is that the waiting time is averaged over one full hour of traffic.You measure your peak hour traffic flow, Jensen said. For Bainbridge, that means when the commuter ferries unload in the evening.When the ferry traffic hits, several of the island’s intersections may have more than a one-minute backup, most notably Madison Avenue and High School Road.But 10 minutes later, the traffic there is gone, Jensen said. The recently approved traffic study will assess LOS levels in the Winslow core. Jensen said he would be surprised if any of the LOS levels fall below level D.If any development threatened to reduce LOS from E to F, then the proposed concurrency ordinance will bar that development unless the city or the developer has a specific plan to restore the LOS within six years and puts up the money to pay for it.The city’s long-range plan is to lure ferry traffic out of downtown Winslow by creating an attractive alternative – up the highway to Madison, which will have a left-turn light, back to New Brooklyn, west to Sportsman Club and down Sportsman to the south end of the island. Under that plan, the roads at the head of the bay would be reconfigured to tie Sportsman directly to the west end of Wyatt Way.Until then, though, islanders need to get used to some downtown traffic, at least when the ferries dock.I know it can seem like forever when you’re in a long line of cars, Jensen said. But it’s intermittent. Think about cities like Phoenix, where traffic is like that most of the day. “