downtown seattle transit capacity white paper final draft

7/21/2019 Downtown Seattle Transit Capacity White Paper Final Draft

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HIGH CAPACITY TRANSIT STUDY

SOUTH KING COUNTY CORRIDORS

2014 FINAL DRAFT DOWNTOWN SEATTLE TRANSIT CAPACITY WHITE PAPER


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INTRODUCTION

ANALYSIS FRAMEWORK

This White Paper presents an analysis of the

possible future of transit demand and

capacity in downtown Seattle. This is a

component of the South King County High

Capacity Transit (HCT) Study.

The central question is whether or notthere will be enough capacity on

downtown Seattle surface streets andin

the existing Downtown Seattle Transit

Tunnel (DSTT) to accommodate potential

additional HCT connections. The HCT

connections under consideration in the

paper are those between downtown and

Ballard, and between downtown and

West Seattle, Burien (and potentially

Renton). If there is not sufficient capacity

on downtown Seattle surface streets

combined with the DSTT, then

consideration of additional capacity willbe required as part of future High Capacity

Transit planning.

REGIONAL BUSES

ST LINK LRT

KC METRO BUSES

SEATTLE STREETCAR

FIG. 1 Principal existing & potential transit corridors in

Downtown Seattle

To address that question, 2035 travel demand and capacity in existing and planned HCT corridors

connecting to downtown Seattle was analyzed. The intent is to explore how HCT service evaluated in

the South King County HCT study could be connected to serve a variety of origins and destinations.

Connectivity and transfer demand were also analyzed using origin and destination information from

Sound Transits ridership model for 2035. This analysis identifies where travel could potentially be

constrained and how future HCT might serve to address those constraints.


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CONTEXT

DOWNTOWN SEATTLE TRANSPORTATION

Seattles Commercial Core and the surrounding neighborhoods comprising the Center City continue to

grow (Figure 2). Significant new private and public investments, as well as growing demand for transit,

are transforming this part of the city. This change is being brought about by substantial private

investment in jobs and housing paired with strong public investment in light rail, streetcars, bike

facilities and the new waterfront resulting from the Alaskan Way Viaduct replacement project. Figure 3

illustrates the new private development and transportation infrastructure projects planned or under

construction as of early 2014.

FIG. 2 Neighborhoods included in Seattles Center City (City of Seattle, Department of Planning and Development)


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I.D . CHI NAT O WN S TATION

FIG. 3 The future transportation network serving downtown Seattle, showing growing public investment in

transportationchoices. (DSA/SDOT Downtown Access Study, VIA Architecture, 2013)


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A RING OF CONSTRAINTS

In 2003 the City of Seattle issued the Center City Circulation Report which presented a comprehensive

conceptual approach for maximizing access to downtown Seattle by improving and integrating public

transit, bicycle and pedestrian networks. This is a macro-scale effort to integrate existing light rail, bus,

monorail, streetcar, ferry terminal, Alaskan Way Viaduct and Seawall (AWVS), and bicycle and pedestrian

projects, all independent transportation projects that will affect future circulation in downtown Seattle.

The Center City report emphasizes that access to downtown Seattle is limited by a ring of physical

constraints. An outer ring limits points of regional access and consists of the Ship Canal and Lake Union,

Lake Washington, the Duwamish Waterway, and Elliott Bay (Figure 4). An inner ring limits access to the

Downtown Core of the Center City. There are few points of accessto and from I-5, Spokane Street and

the Alaskan Way Viaduct (Figure 5).

To Ballard

To West

Seattle

North Link

SR 520

East Link

Central Link

Map Key:

Seattle Center City

Ring of constraintslimitingaccess

Existing and plannedSR 520 Bus Service

Existing and plannedLink light rail service

Existing Sounderservice

Potential Ballardto Downtown and

Downtown toWest Seattle HCTconnections

FIG. 4 The outer ring of constraints (Center City

Circulation Report, SDOT & Nelson/Nygaard, 2003)

FIG. 5 The inner ring and travel through the

Downtown Seattle: existing and planned corridors

However, there are several trends that will improve regional connections in coming decades despite

the mobility challenges posed by geography. A substantial portion of the regions residentialand

commercial growth is occurring within Seattle, particularly in and around downtown, meaning that

more people will be living and working there. Growth in downtown Seattle will provide moreopportunities for work and home locations to be within walking distance of one another, which will

help to alleviate the constraints described above.

Link light rail will provide new points of regional access, allowing travelers to bypass surface

constraints as the network expands north, east and south. However, on-street congestion in

downtown Seattle is projected to increase with additional development, and future HCT planning

may benefit from partnerships between transit agencies and the City of Seattle to ensure reliable

transit travel times.


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CURRENT TRANSIT CAPACITY

King County Metro buses are currently overloaded at peak travel times, both on downtown Seattles

surface streets and in the DSTT. There is a lack of both surface street throughput and available bus

stop curb space on north-south streets at peak travel times, which results in speed and reliabilityissues for bus routes serving downtown Seattle.

FIG. 7 2012 AM Peak Period Downtown Passenger

Load (TMP Briefing Book, Figure 4-18. Data from

King County and City of Seattle)

To understand the nature of these limitations, King County Metro studied bottlenecks in Seattles

Central Business District transit network and published a report identifying the maximum number of

buses per hour that can be accommodated by each Commercial Core street.1 In most cases, the

capacity of a street is constrained by bus stop capacity, or the amount of curb space available for

arriving buses. This King County Metro analysis, performed in anticipation of the end of the Ride Free

Area and pay-on-entry boardings, reveals that stops on 2nd, 3rd and 4th Avenues at Pike Street are at or

over capacity. The DSTT, currently used for both light rail and bus service, is currently operating at its

maximum mixed-mode vehicle capacity, serving approximately 50 buses and 16 light rail vehicles per

hour at peak periods.

Demand in these corridors will continue to grow. To address that growth, Sound Transit and King

County Metro are currently reevaluating their near- and long-term assumptions about the capacity of

the DSTT and the downtown street network for buses and light rail. Because the results of that

evaluation are not yet available, this analysis utilizes assumptions from King County Metro s 2001

Tunnel Capacity Study as well as King County Metros analysis of expected Commercial Core bus stop

capacity after implementation of its pay-on-entry policy in 2012.

As Sound Transit expands Link light rail to reach more travel markets, an increasing number ofregional transit trips will shift to light rail, meaning fewer regional buses will travel on downtown

streets. At the same time, increased Link service will result in headways incompatible with mixed

operations in the DSTT, requiring relocation of buses to surface streets. Link service will intercept

riders outside of downtown Seattle, reducing some bus trips on downtown streets. Although there

will be fewer regional bus routes entering downtown Seattle, any remaining transit capacity on

surface streets could be taken up by growing demand for local bus routes within downtown.

1 Simulation Testing of No Ride Free Area at Selected Critical Bus Stops in the Sea ttle CBDKing County Metro, 2011, pp. 25.


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FUTURE DEMAND AND CAPACITY

GROWTH IN PERSON TRIPS

Between 2011 and 2012, Seattles population grew

at a rate 25% faster than that of surrounding King

County. Citywide, Seattle gained more than 23,000

residents between 2010 and 2012.

More apartments were developed in the Seattle area

in 2013 than in any of the previous 20 years. This will

occur again in 2014 and in 2015.2

The Puget Sound Regional Council has projected

35,000 additional residents and 129,000 additional

jobs will be accommodated in SeattlesCenter City

232,100

2008

361,100

2030

47,500

2008

83,200

2030

22,600

2011

52,500

2035

between 2008 and 2030. Conservative estimates

are that between 3,000 and 5,000 apartments

will be added per year over the next three years.

Center CityJobs

Center CityResidents

Peak Hour TransitTrips Through TheCommercial Core

Approximately three-quarters of those new

apartments will be built in Seattle, most of them

concentrated in the Center City and close-in

FIG. 8 Growth in Center City Jobs, Residents, & Transit Trips

neighborhoods. The supply of office space is also increasingfor example, Amazon, Inc. alone is

adding space for approximately 17,000 new workers between 2014 and 2015.3

As a result of those additional jobs and residents, the number of transit trips taken in and arounddowntown Seattle is expected to grow as well. According to Sound Transits EMME model, the

number of peak-hour transit trips in and around the Center City will more than double by 2035,

increasing by nearly 30,000 trips over 2011 levels in the Commercial Core.

2 Rental market & development trendsDupre+Scott, September 2013

3 http://seattletimes.com/html/businesstechnology/2020775791_apartmentboomxml.html
http://seattletimes.com/html/businesstechnology/2020775791_apartmentboomxml.htmlhttp://seattletimes.com/html/businesstechnology/2020775791_apartmentboomxml.htmlhttp://seattletimes.com/html/businesstechnology/2020775791_apartmentboomxml.html


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ACCOMMODATING BUS, BIKE, AND RAIL

To determine the amount of transit capacity that will be available to meet future travel demand, this

analysis draws upon existing studies from King County Metro4, the City of Seattle5, and input from Sound

Transit, with the following assumptions about the state of the Center City transit network in 2035:

In 2035, Link Light Rail will operate through

the DSTT at three-minute headways using

four-car trains and a load factor of 2.0

(twice as many passengers as there are

seats)

King County Metro buses will continue to

operate at their current load factor (1.05)

Bus volumes on 2nd, 3rd, and 4th Avenues

will remain the same as today, constrained

by curb space and stop capacity

The Center City Connector is planned to connect

the First Hill and SLU Streetcars via 1st Avenue,

running at five- minute headways

Modifications to surface streets, including cycle

tracks and transit lanes, will be implemented when

funding is available as outlined in Seattles Transit

and Bicycle master plans

Based on these assumptions, the capacity of the transit system in the Commercial Core was

calculated. The results are shown in Table 2 summarized for the DSTT and all surface transit

(streetcar, surface bus).

The surface capacity values shown in Table 2 are based on the bus stop constraints and assumed

vehicle load factors. Key to this capacity being delivered is that the transit vehicles can travel through

the Commercial Core without excessive delay caused by other vehicles. An analysis ofthe 2035 Puget

Sound Regional Council travel demand model (which forecasts future vehicle trafficvolumes and

speeds) indicates that the average peak hour speeds on the north/south streets to be approximately 6-

10 MPH. The additional transit lanes proposed in the Seattle Transit Master Plan on 2nd and 4th

Avenues will help to improve transit speeds through the Commercial Core; however, cross street traffic

and turning vehicles could still result in delays to surface transit that could ultimately impact the ability

of surface transit to travel reliably through downtown.

TABLE 2: Funded Peak Hour Transit Capacity

through the Center City In 2035

Facility Corridor Effective Seats6

Link Light Rail DSTT 23-24K

Surface Transit 1st, 2nd, 3rd

4th & 5th

21-23K

Total Capacity 44-47K

4 Center City Connector Transit Study, Tier 2 SDOT & Nelson Nygaard, October 2013

5 King County Metro; Center City Connector Alternatives Analysis

6 Note: Effective Seatsis a measure of capacity and includes stop capacity and load factor. It does not assume all transit

riders have a seat, but rather is used to describe the carrying capacity of a transit vehicle. In this analysis, capacity is

estimated for buses using a load factor similar to what KC Metro experiences today (1.05); for Link Light Rail, capacity is

estimated using the same load factor as is used in Sound Transits long range operating assumptions (2.0)


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FUTURE DEMAND

Future transit demand was evaluated using a transit trip origin-destination (OD) matrix extracted

from the 2035 ST EMME model which includes implementation of ST2 projects. This OD method was

selected because it is difficult to accurately predict which transit routes will serve downtown Seattle

in 2035 with the information currently available7. OD trips are not assigned to individual transit lines,but rather to specific transit modes such as Link Light Rail, surface transit (bus/streetcar). Potential

demand stemming from the Ballard and SKC HCT projects was also identified. Key assumptions used

to estimate demand include:

The geographic boundaries of the different OD areas evaluated define the available transit mode

(see Figure 9). For example, transit trips beginning or ending in First Hill or the Central District

will be accommodated by surface transit, while trips to/from North King County and Snohomish

County will occur on Link Light Rail.

Transfers are assumed to occur within the Commercial Core according to the rates shown in

Table 3. The transfer rates are based on the project team s best judgment based on

observations of existing travel patternsfor example transfers from Sounder to 4th Avenue andDSTT transit. The transfer assumption is a key element of this analysis since transfer trips can

appear to be counted twice, for example on Link and on a surface bus.

The transfer rate varies by types of trips that enter or traverse the Center City. Five trip types

were identified, as shown in Figure 10.

Demand was calculated at three hypothetical screenlineswithin the Center City OD zone. The

north screenline is roughly at Valley Street, the middle screenline is in the Commercial Core,

roughly between Pine and James Street, the south screenline is roughly at Dearborn Street. The

screenlines are not absolute (e.g., at Union Street) because of the OD method being used8. The

goal is to identify the point at which the transit routes are at their fullest as they travel through

the study area. The maximum demand across the each of the screenlines was identified and

summed to estimate total demand.

The results of the demand analysis are shown in Table 4.

7 The Sound Transit EMME model assumes that many routes from the north will be truncated as Link extends north of the

University of Washington. There are also potential truncations for service as East Link is built. However, with fewer long-

distance routes, King County Metro could re-deploy transit hours to serve Center City trips and other neighborhoods near the

Center City with additional service, since transit demand is expected to be high. Considering that the Sound Transit model is

not capacity constrained, it is likely that additional bus service not explicitly assumed in the model would be required to meet

the high transit demands forecasted under 2035 conditions. This OD method, combined with a fixed bus load factor of 1.05assumes that additional bus service will be provided in the future.

8 The OD method assigned 30% of intra-Center City trips and 75% of trips that transfer from Link/Sounder to surface transit

to the cross the middle screenline. This method was chosen to simplify the assumptions about which specific stop within the

Downtown Commercial Core people get on and off at.


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TABLE 3: Downtown Surface Transit between Origin and Destination Pairs 2035

Origin/Destination PairsAssumed

Transfer RateNotes

Travel to Center City via Link Light

Rail, Bus, or Ballard/SKC HCT

30% This assumes that some trips will be made via a transfer

to a bus in the Commercial Core. For example, travel from

West Seattle to South Lake Union or from Ballard to theStadium District

Travel to Center City via Sounder

Commuter Rail

75% Assumes many trips on Sounder will transfer to surface bus

to reach the final destination within the Center City.

Travel to First Hill/Central District

via Markets Served by Light Rail, ST

Regional Bus, Ballard/SKC HCT or

Sounder

100% Assumes that all long-distance regional trips will transfer

to a bus in the Commercial Core to reach First

Hill or the

Central District. No transfers are assumed from Capitol

Hill or the Center City.

TABLE 4: Projected Peak Hour Demand

for Center City Transit Facilities In 20359

Facility Trip Demand

Link Light Rail (DSTT) 18-20KSurface Transit 25-27K

Potential West Seattle/

Ballard HCT

6-8K

Total Demand 49-55K

North Link

Kirkland/Redmond

(520)

Ballard

Center City

(Area of Study)

First

Hill

Capitol

Hill

Central

District

I-90 / East Link

West Seattle /Burien

Central Link /

Sounder /

ST Express

Extents of Center City assumed inDemand analysis

Trips occurring outside of Downtown

FIG. 9 Trips On Downtown Transit Corridors Occurring Outside the Center City

9 King County Metro; Center City Connector Alternatives Analysis


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VARIABLES

Understanding the capacity of a specific facility

requires determining which origins and

destinations travelers using that facility are likely

to require, and how proposed and existing

connections will facilitate those trips.

Trip Types

In the Center City, there are at least five different

trip types possible given various origin

destination pairs (see Figure 10). Each places a

different demand on the capacity of the facilities

it uses. For a specific trip, this distribution ofdemand can depend on several factors, such as:

The number of riders requiring a trip through

the Center City

The number of riders using a facility for trips

within the Center City

Whether a rider arrives close enough to walk

to their final destination, or whether their

trip requires them to transfer to an

intermediate mode or facility

Trip Distribution

Constraints inherent in Seattles current and proposed transit facilities also pose challenges for

particular trips, including trips made by riders arriving at King Street Station via Sounder commuter

rail who need to travel to destinations north through the Center City; trips made by riders arriving in

the Center City via Ballard HCT who want to continue south; or trips made by the growing number of

people living and working in the Center City who need to reach key Center City destinations such as

the stadiums. It is also important to consider instances in which demand is so high at DSTT stations

(such as the InternationalDistrict /Chinatown Station or at Westlake) that riders are not able to board

trains because they are full.

Understanding the capacity of any corridor requires assumptions about trip distribution as transitvehicles move through the Center City. In an idealized scenario, the number of riders departing a

vehicle at any given station would be equal to the number of riders boarding that same vehicle, such

that seats would be available to all boarding riders. If this were the case, capacity of a given transit

corridor could be designed simply as a factor of the number of transit trips into and out of the Center

City made via that corridor.

Fig. 10Possible Center City Trip Types


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jobs andpeople.

sandpeople.

jobsand people.

bsandpeople. bsandpeople.

sandpeople.

jobs andpe ople.

jobs andpeople. sandpeople.

jobsand people.

bsandpeople.

jobs andpeople.

sandpeople.

jobsand people.

bsandpeople. bsandpeople.

sandpeople.

jobs andpe ople.

jobs andpeople. sandpeople.

jobsand people.

bsandpeople.

WESTLAKE

WESTLAKE

MADISON

MADISON

INTLD

IST

INTLD

IST

COMMERCIAL CORE

PERFECT TRIP DISTRIBUTION

DEMAND = CAPACITY

BALLARD HCT

job

jo

job jobjo

jo

WEST SEATTLE/

BURIEN HCT

MAXIMUM

DEMAND

ADDITIONAL TRIPS

THROUGH AND WITHIN

COMMERCIAL CORE

EXCEED CAPACITY

COMMERCIAL CORE

IMPERFECT TRIP DISTRIBUTIONDEMAND > CAPACITY

BALLARD HCT

job

jo

job jobjo

jo WEST SEATTLE/

BURIEN HCTMAXIMUM

DEMAND

FIG. 11 Trip Distribution in Center City Transit Corridors

In reality, trip demand along transit corridors is often distributed unevenly among various stations and

asymmetrically between directions of travel, requiring additional capacity where theres a high potential

for overlapping trips (see Figure 11). For example, if riders wishing to board a northbound train at a

station in the Commercial Core are faced with a full train of riders headed to points north that have not

yet left the train, twice the vehicular capacity is needed in order to accommodate both sets of riders.

This analysis assumes that in reality, the trip distribution will be somewhere between the perfect case

scenario (0% trip overlap) and the worst case scenario (100% trip overlap), and splits the difference

between the two at the midpoint of trip distribution.


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OVERALL CAPACITY VS. DEMAND

After accounting for trip growth and planned capacity, the

analysis found that demand on transit routes traveling through

the Commercial Core; including the potential HCT corridors

evaluated between Ballard, West Seattle, Burien, and Renton;

will exceed the capacity of existing and planned facilities in

2035. While this aggregate finding is informative about general

transit demand in Seattles Center City, it does not fully describe

the value of specific facilities in accommodating likely travel

origins and destinations. Tables 2 and 4 describe a discrepancy

of approximately 5,000 - 8,000 effective seats9 between

anticipated future peak hour demand and capacity on Center

City transit facilities.

Trip demand was calculated by breaking Center City trips down

into origin and destination pairs, then assigning each trip to

the Center City transit mode most likely to serve each origin

and destination. Demand was assessed for each mode at the

north and south edges of the Center City, as well as within the

Commercial Core were highest trip volumes were expected to

occur. Next, the point of highest demand was

identified for each mode and assumed to be the controlling factor

in the capacity needed to accommodate that mode.

FIG. 12 Third Avenue Transit Corridor at peak

hour

9 Note: Effective Seatsis a measure of capacity and includes stop capacity and load factor. It does not assume all transit

riders have a seat, but rather is used to describe the carrying capacity of a transit vehicle. In this analysis, capacity is

estimated for buses using a load factor similar to what KC Metro experiences today (1.05); for Link Light Rail, capacity is

estimated using the same load factor as is used in Sound Transits long range operating assumptions (2.0).


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WHERE CAN ADDITIONAL HIGH CAPACITY TRANSIT BE

ACCOMMODATED?

The central question addressed by this study is whether the capacity planned for Center City transit

facilities will be adequate to accommodate potential additional HCT service along with expectedgrowth in Center City transit trips, or whether additional capacity will be required as part of a future

HCT investment. The study evaluated Sound Transits ridership forecasts for HCT service connecting

Ballard, West Seattle, Burien, and Renton to the Center City, and predicts demand for an additional

6,000 to 8,000 trips through the Commercial Core. The study also found that the north-south

avenues in the Commercial Core as well as the DSTT are both operating near their maximum

capacities and will continue to do so until 2035, meaning new transit capacity through the Center

City will be required. There are several options for how to accommodate new capacity, each with its

own benefits and challenges. The following options discuss both how additional HCT service could

be accommodated, while also addressing the finding that overall additional transit capacity will be

needed through the Commercial Core.

Bus Rapid Transit (BRT)

To accommodate demand for Ballard/West Seattle/Burien/Renton BRT service

and for buses serving other corridors, up to two bus-only lanes could be

considered in each direction on 2nd and 4th Avenues through the Commercial

Core (as proposed in the Seattle Transit Master Plan). This reconfiguration of

existing street width could allow for buses to pass each other, similar to existing

operations on 3rd Avenue.

Benefits and Challenges

Low capital cost but medium to high operations cost

Bus operations in the Commercial Core are limited by a finite amount of curb

space

Will require transit-only lanes in existing right-of-way A surface alignment will face significant speed and reliability issues in the

Commercial Core due to increased traffic volumes, cross street congestion,

signal timing requirements, turning vehicles and pedestrian movements

Grade Separated Rail-Only Facility

Whether elevated or underground, an additional grade-separated alignment

through the Center City would accommodateprojected demand for Ballard

and West Seattle/Burien/Renton HCT, but would likely only accommodate

someunmet surface transit demand.

Benefits and challenges

Grade-separation provides reliability. Without a transfer , a grade separated rail-only facility does not accommodate

trips to and from neighborhoods served only by bus

Structural supports required for an elevated alignment could potentially reduce

surface street capacity.


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New Rail/Bus Tunnel(s)

In addition to serving Ballard and West Seattle/Burien/Renton-bound riders,

a tunnel or tunnels accommodating both rail and bus vehicles would have

serve multiple travel markets, reliably accommodatingmost unmet demandfrom surface-routed corridors.

Benefits and challenges

Accommodates demand for rail and bus trips

Provides reliable travel time

Relieves demand for almost 60% of on-street capacity

Requires integrated stations/hubs to transfer

Requires multi-agency coordination and funding

Requires rerouting of buses to access tunnel

Peak Hour:

Projected Demand For New HCT: 6-8K trips10

60% of Unmet Surface Demand: 2-3K tripsTotal Demand for Rail/Bus Tunnel: 8-11K trips

Transfers and Connections

WESTLAKE

HUB

STADIUM

STATION

For the best return on investment, a new HCT line through downtown Seattle

will simultaneously offer a reliable connection to the markets it serves directly

as well as alleviate unmet transit demand. The amount of service that can be

accommodated by a grade separated alternative depends greatly on station

locations and the quality of transfers to and from connecting

transit facilities.

For example, a shared-use bus/rail tunnel would be most effective if portals

were configured to provide reliable travel time for bus routes that will

continue to use Aurora, Dexter/Westlake, Stewart/Olive, and the SODO Bus-way to access the Center City. A rail-only tunnel could also offer useful capacity

for DSTT riders, but only if seamless transfer opportunities are provided at

downtown transit hubs such as Westlake Station. Connections and transfers

south of the Commercial Core that take into account the year-round calendar

of stadium events will be very important.

In all cases, improved connections and wayfinding at the Westlake Station

transit hub will be necessary to connect any future HCT facility to Link Light

Rail service in the DSTT, as well as to surface buses serving South Lake Union

and origins east of the downtown. South of the Commercial Core, improved

transfers and wayfinding between new HCT service, Link Light Rail, Sounder

service, and bus routes will further expand each facilitys demand and capacity.

10 Source: Sound Transit EMME Model, including Ballard to Downtown and South King County HCT studies.


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