Seattle Light Rail's Fatal Flaw

The Preface to the 2008 Draft and 2011 Final East Link Project Environmental Impact Statements include the following statement regarding the selection of light rail for I-90 high capacity transit (HCT)

Local, regional, and state agencies have been studying high-capacity transportation alternatives to connect Seattle with the Eastside of King County since the mid-1960s.  In 2004, the Puget Sound Regional Council (PSRC) prepared the Central Puget Sound Regional High Capacity Transit Corridor Assessment to establish a basis for more detailed planning studies and environmental analysis.  The report found that the cross-lake corridor, connecting the urban centers of Seattle, Bellevue, Overlake and Redmond, had the highest potential for near-term development of high-capacity transit (HCT) alternatives. Sound Transits updated Long-Range Plan (2006) includes HCT across I-90 serving these urban centers, and the Sound Transit Board has adopted light rail as the mode for this corridor, now referred to as the East Link Project.

Section 3 of the PSRC study included a survey of several HCT options and an assessment of their capabilities.  Enhanced bus, bus rapid transit (BRT), and light rail were the most applicable to cross-lake service.    

The study compared each option in terms of their people per hour per direction (pphpd) obtained by multiplying the number of potential riders in each vehicle by the number of vehicles per hour.  They considered the buses to operate as “platoons” of two or four together with 4-minute intervals (headways) between “platoons”.  The primary difference between the enhanced bus and BRT was the enhanced buses could accommodate up to 80 riders vs. 90 for BRT.  The resulting capacity for the 2 and 4-platoon enhanced buses was 2400 and 4800 pphpd and 2700 and 5400 pphpd for BRT,

The PSRC light rail analysis assumed each 74-seat car could accommodate 148 riders with 4-minute headways between trains.  Again, 2 and 4-car trains were assumed giving a capacity of 4440 and 8880 pphpd for light rail.  Thus along a single route, light rail has a greater capacity.

The problem in Seattle is the tunnel restricts light rail to a single track in each direction or 8880 riders per hour (rph).  Assuming half of the capacity will be diverted to East Link the maximum cross-lake capacity is 4440 pphpd or 8880 in both directions with 4-car trains and half those levels with the more likely 2-car trains (see below).  Both of these capacities are a small fraction of the 24,000 rph Sound Transit has promised for East Link.

The only cross-lake restriction on BRT frequency is providing minimum headways for safety between subsequent buses.  Each bus-only lane can safely accommodate up to 1000 buses per hour. (60,000 pphpd with 60 passenger buses)  The lanes could provide direct bus routes from every east side P&R into Seattle to one or two dedicated drop off points along 4^th Ave and pick-up points along 2^nd Ave for the return route.  (Both avenues would be restricted to buses only at least during peak commute hours.)  

The BRT access at each P&R as well as Bellevue T/C could provide eastside commuters with cross-lake capacity that dwarfs light rail at a tiny fraction of its cost.  Thus it’s clear the Sound Transit Board made a monumental blunder when they “adopted light rail as the mode for this corridor, now referred to as the East Link Project”.

The problems associated with the tunnel limits go far beyond East Link.   Maximizing Central Link ridership requires operating 4-car trains at least during the peak morning and afternoon commute hours.  However, their high operating costs ($24 per mile per car) result in prohibitively expensive trip costs for the 13-mile extension to Lynnwood and the 11 miles to Federal Way.  

Sound Transit has a choice.  They can accept the 4440 pphpd tunnel capacity with 2-car trains and operate the light rail extensions to Lynnwood and Federal Way.  (obviously East Link trains would also be limited to 2 cars.) The operating costs will still far exceed fare box revenue, which along with the extension construction costs will be a perpetual drain on the areas transportation funds.  

The other option is to avoid spending the $20 billion on the Prop 1 extensions, limiting Central Link to connections between University and Sea Tac, and initiating BRT service on I-90 and 520.  Also create a T/C at the University Station as an interface between the 520 BRT service and Central Link light rail.  The 4 car trains would provide the capacity for the thousands of BRT riders in both directions and make Central Link operations financially viable.    

This shouldn't  be a difficult choice!