Why ST3 Can’t Reduce Congestion

A PSRC 2015 “Stuck in Traffic: 2014 Report” details the thousands of hours commuters are delayed by congestion on the area’s freeways.  Even those able to use HOV lanes are experiencing 75-minute commutes between Everett and Seattle and 55 minutes between Federal Way and Seattle.

The report’s “Commute Mode Share” chart shows that roughly 85% rode in cars, with ~10% of those in car pools, while ~10% used transit.  The obvious way to reduce delays for everyone is to convince more of those who ride cars to switch to transit.   The best way to do so is to provide them with the option of leaving their car at a P&R near where they live with access to transit with capacity to take them to near where they work.

The problem with the parking part of the solution is that the approximate 20,000 spaces in P&R lots in Snohomish, King, and Pierce counties for those commuting to Seattle or Bellevue are essentially already “in use”.  Thus thousands of added parking spaces are needed at existing or new P&R lots to attract additional transit commuters.  Yet neither Prop 1 nor ST3 include the billions required for the additional 50,000 or more parking spaces needed.  (While that seems like a lot commuters have to park their car someplace and it’s likely to be cheaper near where the live rather than where they work)

Once they provide the added parking reducing congestion requires providing commuters with access to transit with sufficient capacity to take them to within acceptable distance of where they want to go. The two options are routing the connecting buses to light rail stations or routing them directly into Seattle (or Bellevue and Overlake T/Cs).   Buses benefit from having the flexibility to be used on routes that don’t justify light rail service.  More importantly light rail in Seattle doesn’t have the capacity needed to significantly reduce congestion.

A 2004 PSRC report concluded the tunnel limits Prop 1 maximum capacity to 8880 riders per hour (rph) in each direction. They based that capacity on their conclusion the tunnel limited light rail to one 4-car train every 4 minutes and that the 74-seat cars can reasonably accommodate 148 riders.  Assuming that capacity is split between East Link and south Central Link limits their capacity to 4440 rph each.  These light rail capacities are less than what’s currently available with buses.

At best Sound Transit could continue with current bus routes and use light rail to increase transit capacity.  They would still have to provide the as yet unfunded added parking with bus routes to light rail stations.  The limited capacity also means light rail cars could be full before they reach some of the light rail stations nearer Seattle during peak commute.  

Sound Transit could achieve the increased capacity of light rail in Seattle for a fraction of its cost by adding BRT routes from the added parking   A 70 ft articulated bus can accommodate a total of 119 sitting and standing riders.  Each bus can be routed from one or two P&R lots directly into Seattle.  Eighty such buses an hour would more than match Central Link capacity along north I-5 and forty would match East Link and south Central Link capacity. 

The benefits of potential BRT capacity go way beyond simply matching light rail.  A bus-only lane can accommodate more than 900 buses an hour.  If one of the two I-5 HOV lanes between Everett and Seattle were limited to buses during the peak commute, transit capacity would exceed 100,000 rph, dwarfing foreseeable requirements.  The only limit would be the needed parking and buses.      

The same capacity would be available on the I-90 Bridge center roadway if it were divided into inbound and outbound BRT lanes rather than light rail.  (Sound Transit plans for light rail on center roadway will increase cross-lake congestion for vehicles.) Less frequent BRT service on SR 520 Bridge and Central Link south of Seattle could be facilitated with +3HOV requirement during peak commute. Egress and access for all the bus routes in Seattle could be facilitated by converting 4^th Ave into an elongated bus-only T/C with one or two designated drop off and pick up locations for each BRT route 

The bottom line is without additional funding for parking and bus routes to light rail stations Sound Transit’s $54 billion ST3 package will have a “miniscule” effect on congestion.   That even with this additional funding ST3 won’t have the capacity to significantly reduce congestion and pales in comparison to what could be achieved with BRT in a fraction of the time and for a fraction of the cost.