WSDOT Problems Beyond Bridge Oversite

The May 18^th Seattle Times Traffic Lab article “Report: Time running out to salvage West Seattle Bridge” details how the bridge must be shored up to keep from collapsing under its own weight.  Clearly the bridge cantilever design was flawed from the beginning, whether from lack of depth at the mid-span to support its 590 ft length, lack of adequate post tensioning steel, or segmented construction.  (A retired Boeing propulsion engineer “suggested” solution could be a temporary mid-span support from below with long term plans for support from above with suspension cables from towers added to piers.)

However, the WSDOT oversight of the West Seattle Bridge is far from their first bridge failure. First there was the Tacoma Narrows Suspension Bridge.  It opened to traffic on July 1, 1940 and collapsed into Puget Sound on November 7 the same year. The original I-90 Floating Bridge sank in 1990 as had the Hood Cannel bridge eleven years earlier.  The original ST 520 Bridge was structurally deficient.  Its replacement endured costly delays due to design and construction problems and opened a year and a half late.

East Link was the first attempt to install light rail on a floating bridge.  The WSDOT used flat bed trucks to simulate light rail cars on I-90 Bridge to conclude “the test confirmed previous findings that the bridge can be structurally retrofitted to carry the loads associated with the light rail system under consideration, in addition to general traffic on the roadway”. 

It took an FHWA and legislature funded Joint Transportation Committee to convince WSDOT more testing was needed.  It remains to be seen how long the interface between the fixed and floating parts of the bridge can withstand the loads from four heavily loaded light rail cars.

The WSDOT problems go beyond bridge design and construction oversight to an apparent failure to understand transit basics.  Transit capacity is defined by the number of vehicles per hour times the number of potential riders in each vehicle.   The PSRC concluded in 2004 the Downtown Seattle Transit Tunnel (DSTT) limited light rail to 60 light rail cars per hour and that each 74-seat car could accommodate 148 riders or 8880 riders per hour. 

Yet the WSDOT agreed to Sound Transit splitting that limited capacity between Central Link south and East Link leaving neither with adequate transit capacity for future growth.  Even more egregious they allowed Sound Transit to confiscate the I-90 Bridge center roadway precluding two-way BRT with 10 times light rail capacity at 1/10^th the cost, 10 years sooner.

The WSDOT response to the Freeman litigation objecting to bridge confiscation convinced a federal judge the I-90 Bridge center roadway wasn’t needed for vehicles and thus could be used for light rail.  They simply ignored a 2004 FHWA study conclusion that, even with the 4th lanes added to outer roadways, the center roadway was needed for vehicles.  Increased I-90 Bridge congestion since center roadway closure validates FHWA concerns.

They’ve abetted Sound Transit plans to use East Link to replace cross-lake buses rather than add transit capacity.  Apparently not realizing bridge congestion was not due to too many buses.  Sound Transit “bus intercept” agreement with Mercer Island requires they and King County Metro halve current I-90 corridor vehicles, halving capacity.  East Link operation in 2023 will demonstrate the WSDOT abetted spending billions on a transportation system that increases congestion along the entire I-90 corridor into Seattle.

The WSDOT approach to I-405 congestion shows a failure to understand basics of lane capacity.  A lane’s maximum vehicle capacity is obtained by limiting traffic to 2000 vehicles per hour (vpr), assuring 45 mph.   HOT lanes improve HOV velocities by raising fees to reduce the number of vehicles from carpoolers to what’s needed to limit traffic to the 2000 vph. 

The WSDOT decision to impose HOT on two I-405 lanes is based on their “unique” assumption HOT fees increase lane capacity.  The slower HOT lanes with the 2^nd HOT lane along Lynnwood-to-Bellevue route have already debunked the assumption.  The problem being, during much of the commute, the 2^nd HOT lane increased GP congestion on remaining lanes, attracting more than 2000 vehicles willing to pay the WSDOT fees on the two lanes.  The result being GP lanes have slowed and HOV lanes have failed to achieve 45 mph for those paying for HOT.  Future growth will add to both problems.

In 2017 the WSDOT announced plans to begin adding 4^th lanes between Renton and Bellevue in 2019, again imposing HOT fees on 4^th lanes as well as on existing HOV lane.  One can only hope the delay is due to their belated recognition that HOT should be limited to one lane with fees raised to limit traffic to 2000 vph and use additional lane for GP traffic.  Again one can hope they’ll do the same to I-405 between Bothell and Bellevue.

The bottom line is the WSDOT history of failing to effectively oversee the design and construction of the area’s bridges has cost the area.  However those problems will eventually be resolved.  Far more damaging is their slavish support for Sound Transit Prop 1 extensions.  WSDOT abetting of Sound Transit refusal to add bus transit capacity shows their failure to understand the basics of public transit. That I-405 congestion will continue to increase on both GP and HOV lanes until WSDOT limits HOT to one lane.