Density done right could alleviate traffic congestion, but no one is considering the cumulative impact of spiked demand for access and service to a new round of towers in downtown Seattle.

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Seattle has learned the hard way that an overturned fish truck or sudden protest can grind all downtown traffic to a halt.  But permanent gridlock is coming from a cluster of skyscrapers now nearing approval without space to contain their own moving and delivery functions.

In our hypergrowth environment, builders prioritize density and revenue-producing space over that for loading and maintenance. They downplay tower impacts on the transportation system and assume existing streets and right-of-ways will serve their demands. This comes at the public’s expense.

With streets strained to capacity, the city now requires vehicle access to buildings funnels through alleys. In two square blocks between Stewart and Lenora Streets from Third Avenue to Fifth Avenue, alleys 16-18-feet wide will do the work of arterials carrying traffic for 11 new projects with 2,000 parking stalls and more than 10,000 residents, hotel guests and workers.

Down narrow alleys, each mega-tower will generate an average 1,000 new vehicle trips a day. Even with a mandatory two-foot setback, the alleys won’t support continuous two-way traffic because they’re lined with three-to-five-foot waste bins.

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Density done right could alleviate traffic congestion, but no one is considering the cumulative impact of spiked demand for access and service to mega-towers. Their outsize traffic will compete with that of existing buildings, many of which lack self-contained space for moving, deliveries and waste collection.

Service trucks without parking will block alleys, creating backups and slowdowns that will be felt by hundreds of cars, trucks and emergency vehicles on adjacent streets.

Alleys may be a space for traffic innovation, but not as they were designed for Seattle 100 years ago. The city has studied downtown congestion but shows no urgency to require tower designs contain their transportation impacts.

A 2016 study by the University of Washington and Seattle Department of Transportation (SDOT) surveyed capacity for individual streets, alleys and buildings in the city core. The report was named “The Final 50 Feet” because that’s where deliveries get bogged down as truck drivers jockey for parking or are delayed riding skyscraper elevators to make deliveries.

It finds even without population growth, delivery trips to the city core will double within five years due to e-commerce.  Further, 87 percent of buildings downtown must depend on the city’s curbs and alleys for deliveries.

As neighbors who live nearby and share an alley with some of the largest planned towers, we’ve attended Design Review meetings appealing for towers to include enough self-contained, accessible loading space to keep trucks from blocking alleys that will now carry thousands of cars a day. So far these requests have been met with a collective shrug.

At a recent review meeting for a 44-story tower with 900 residents and a large restaurant, the architect proposed a single loading berth with maximum capacity for a 17-foot U-Haul truck.  When his turn radius diagram showed the truck couldn’t access the berth, he explained, “that was something the public requested, and we were just checking off a box.”

At that same review meeting, the board was instructed not to consider transportation design in its decision. But once a tower’s design passes, there’s no chance of converting a grand lobby or restaurant into space for moving, delivery and waste collection for a vertical village of 1,000 people.

Current municipal codes give building requirements for loading and waste collection, but some specifications, notably loading for residential towers, are left to the city’s discretion, and developers frequently request departures or outright exemptions.

Developers have also sought to reduce infrastructure requirements by offering loading-management plans. As yet untried, these include posting no-parking signs, requesting truck deliveries be made on a schedule and, in some cases, naming a dock manager.  Not part of city code, the plans rely on voluntary compliance and are meaningless without enforcement and similar plans for all buildings on the alley.

Facing a “period of maximum constraint,” the city is desperate for proactive transportation solutions. A new report confirms the ’50 Feet’ study, and SDOT now says it will examine standards for site and building designs for future developments.

That will be too late. The city should start immediately with towers under approval, applying the maximum current requirements for loading and maintenance design. If it fails to act now, Seattle streets will be crippled for decades.