Highway 520's the better transit choice

As part of the failed Proposition 1 ballot measure in November, Puget Sound voters were asked to authorize $4.7 billion in bonds to fund expansion of Sound Transit's high-capacity transit from downtown Seattle to Redmond, via Bellevue, along the Interstate 90 corridor.

From the perspective of cost, disruption, number of employees served, and population per square mile along the rail corridor, a Highway 520 route is more logical.

The plan for high-capacity transit — light rail — on the I-90 floating bridge was adopted in May 1996, more than 11 years ago. Over that time, such significant change has occurred in the Seattle-Redmond corridor that Sound Transit's proposed I-90 route needs a thorough reconsideration.

Since the Washington state Department of Transportation already plans to replace Highway 520, high-capacity transit could be a part of that right of way. The 520 route would provide a much more direct link to Redmond from the University of Washington light-rail station.

The distance between Seattle's Pioneer Station and Overlake is 14.5 miles along the I-90 route. From the University Station, it is 9.93 miles along the 520 route to Overlake, including a spur down I-405 to central Bellevue.

The population served along each right of way (within approximately one mile of the transit line) is about 84,000 (3,845 people per square mile) along the I-90 route, and 45,400 (3,645 people per square mile) along the 520 route.

More importantly, though, are the key burgeoning employment centers that will be directly tied together with the 520 route: South Lake Union, UW and Microsoft. By 2020, it's estimated that 45,100 more employees will be added to the current South Lake Union/university/Redmond base of 113,300 workers. They'd be separated by a distance of 11.8 miles along 520, versus 18.7 miles on the I-90 route.

In its light-rail system, Sound Transit would provide high-speed/high-capacity service with few stops between high-density employment centers, in comparison with Metro bus service, which provides many stops — some 9,500 — over a vast, low-density residential network.

Cost is another important consideration. Sound Transit's most recent cost estimate for the Pioneer Square-to-Overlake route is $2.54 billion in 2006 dollars, or about $175 million per mile for 14.5 miles.

Assuming the same cost per mile for the 9.93-mile 520 route — same lake, and similar topography and right-of-way acquisition challenges — its cost would be $1.74 billion; only the segment from the university to Redmond with the Bellevue spur would be required. This is an $800 million savings, or a 31-percent decrease in cost.

Based on our initial analysis of costs and other factors, it seems logical to give serious consideration to a high-capacity transit route on Highway 520, rather than along Interstate 90.