Capacity Analysis

There are a number of critical flaws in the proposed East Link system; insufficient capacity, unresolved engineering issues, bus transfer location, and lacking consideration of reasonable alternatives.  Each of these raise significant issues which have not been adequately addressed, given the public safety, fiscal and mobility impacts at stake.

Capacity Analysis

The primary selling point of transit and East Link in particular is that is buys us extra capacity in the system.  The analysis in this section is focused on providing as close to apples to apples comparison of the floating bridge capacity with and without the Light Rail system.

Data for this analysis is based on the Task 9 Report and East Link FEIS <add links>

Light Rail Capacity
8 minute headway (7.5 trains per hour max)
4 car trains
200 max capacity per car
6400 persons per hour absolute max

Lane Capacity
Assuming no change from current 3 outer roadway / 2 HOV configuration the forecast demand from the FEIS provides the detail to estimate the capacity of a single lane.  There are lots of factors that determine actual lane performance. 


40,900  I-90 PM East-bound 3 hour vehicle demand (2010)
13,633 vehicles per hour
5 lanes (3 outer lanes + 2 HOV)
2,726 vehicles per hour/per lane
1.2 persons per vehicle
3,272 persons per hour per lane

58,400 I-90 PM East-bound 3 hour vehicle demand (2030)
19,466 vehicles per hour
5 lanes (3 outer lanes + 2 HOV)
3,893 vehicles per hour / per lane
1.2 persons per vehicle
4,672 persons per hour per lane

The 2030 numbers represent a significantly degraded level of service, but from experience we know what the PM commute looks like with ~3000 vehicles per hour.

I would love to put transit mix numbers into this analysis but the way it was done in the FEIS, it conflates the SR520 numbers with the I-90 ones, so it is not possible to easily determine how much existing transit capacity is provided/consumed solely on I-90.    That said, an articulated bus can hold ~150 passengers and simply running a bus at the same interval as the train would provide 1/4 of the capacity that the train provides while having no meaningful impact to other vehicle traffic. 

 

 

East-side bus / train transfer (a.k.a bus turn-around)

Alternatives not considered / dismissed