Public Interest Transit Forum -

Addressing SR 520 Corridor Transportation Problems Through a Least- Cost Planning Approach


Dick Nelson and Don Shakow

Institute for Transportation and the Environment

Seattle, Washington


It is suggested that the private sector proposal to apply tolls to the SR 520 corridor (that is, the Evergreen Point Bridge across Lake Washington connecting Seattle to Bellevue) for the purpose of expanding the capacity of the corridor be modified, and that the alternative proposal be subjected to a least/full cost analysis. Rather than expanding the capacity of the corridor, the alternative proposal would use tolls (congestion pricing) to create free-flow traffic conditions for transit and rideshare vehicles. Toll revenues would be used to mitigate prior environmental impacts in the corridor and to more comprehensively enhance travel for transit riders, bicyclists, and pedestrians using the corridor.

Environmental enhancements could include lids over portions of the roadway, noise barriers, quieter roadway surface treatments, water pollution control systems, and the removal of unused freeway exit and entrance ramps. Transit and non-motorized improvements could include improved transit service in the corridor, a personal rapid transit (PRT) system connecting bus routes on I-5 and SR 520 and serving destinations at and around the University of Washington, better connections for transit and HOV's from SR 520 to I-5 and Downtown Seattle, a bike/pedestrian lane on the Evergreen Point Bridge, and a more direct route for utilitarian bicycle trips from Montlake to Eastlake and the Seattle CBD. In addition, existing roadway structures could be seismically strengthened.

The efficacy of the alternative proposal in improving traffic conditions, creating expanded travel mode choices, and reducing environmental impacts could be tested using a least/full cost methodology and model developed by a research team associated with the Institute for Transportation and the Environment (ITE). An economic analysis using the model would compare the social benefits derived from the private sector proposal to those derived from the alternative proposal.

I. Scope of transportation and related problems in the SR 520 corridor

Congestion on SR 520 and I-90

Since drivers crossing Lake Washington have a choice between SR 520 and I-90, the growth of traffic in both corridors is of interest. Current vehicle volume on SR 520 exceeds capacity (Level of Service D or greater) for several hours of each day. At times in both AM and PM commute periods, volume falls off drastically from peak volume as overloading and stop and go traffic occurs. The average weekday volume on SR 520 in 1992 was 53,000 vehicles in each direction. The average weekday volume in 1992 on I-90 was about 55,000 vehicles in each direction. Very little delay has been experienced on I-90 since the new bridge was completed and the old bridge, which sank, was replaced.

The two parallel bridges crossing Lake Washington have a total of 8 lanes in each direction, 2 on SR 520 and 6 on I-90. Three of the I-90 lanes are reversible HOV lanes. Current (1990) total daily (weekday) vehicle volume in both directions across the two bridges is 231,000. Daily volume is predicted to increase to 319,000 in the year 2020 if none of the regional transit improvements now under consideration are implemented. If the HOV lane system is completed and bus service increased (Regional Transit Project's TSM alternative), the daily volume will be 311,000. This compares to the vehicle capacity of the two bridges between the hours of 6 AM and 10 PM (when 95 percent of the daily traffic occurs) of 468,000. The rapid rail system proposed for I-90 in the Regional Transit Project would have reduced daily vehicle trips to 300,000 in that year. Although a similar figure is not available for the Regional Transit Authority's proposed light rail system, an equally small impact on vehicle trips would be expected. Consequently, congestion in the two corridors, particularly on SR 520, is likely to grow significantly.

Community/Environmental Impacts

The SR 520 corridor across Lake Washington was constructed before highway builders were required to mitigate environmental impacts, particularly the harm caused to sensitive ecological areas, noise effects on humans, and the physical division of communities. SR 520 was built through and over significant wetlands and across a corner of Seattle's unique Washington Park Arboretum. The roadway also cuts a swath through two preexisting Seattle neighborhoods, Montlake and Portage Bay/Roanoke Park.

On its eastern extremity, SR 520 skirts the southern end of Fairweather Bay where a wetland was filled in conjunction with the building of the roadway. Since the completion of SR 520, two nature preserves have been established immediately adjacent to the corridor. Pollution carried by runoff from the roadway surface and from the site of the old toll plaza enters Fairweather Bay.

Because of the roadway's design and the topography through which it passes, the corridor has a significant noise impact on surrounding residential areas. Studies of the noise problem have been made, but there has been no action taken to mitigate the problem. Several measures are available, ranging from lids over the roadway to walls, berms, and low-noise roadway surfaces. The construction of lids would involve significant costs, perhaps several hundred million dollars.

SR 520 contributes in several ways to the heavy traffic volumes experienced by Seattle neighborhoods at the west end of the corridor. Congestion in the corridor generates significant volumes of spill-over traffic through the neighborhoods, particularly in Montlake. On and off ramps in the Arboretum and Montlake attract drivers from large areas of northeast and east central Seattle. A related problem is the contribution the SR 520 corridor makes to traffic volumes through the Arboretum. The one two-lane road through the Arboretum serves as a convenient conduit for traffic originating in Seattle and heading to Bellevue and as a shortcut to the Montlake Bridge.

Several SR 520 access and egress ramps were constructed that were intended to connect with a north-south freeway on the west side of the lake. Although this roadway project, the R. H. Thompson Expressway, was abandoned, several of the ramps in the Arboretum area were left in place.

Water pollution related to vehicle travel is also a problem in the SR 520 corridor. Since the corridor was not built with a collection system to capture and filter water, run-off from the roadway surface carries hydrocarbons and heavy metals into Lake Washington and Union Bay.

Transit Problems

The SR 520 corridor presents several serious problems for cross-lake bus travelers. The most obvious and severe is delay caused by congestion. Buses between Bellevue and Seattle are forced to move at the same speed as all other traffic from the east end of the Evergreen Point bridge where the HOV lanes end to the merger of SR 520 with I-5. At that point, buses heading west often encounter congested general purpose lanes on I-5. No ramps connect SR 520 with the I-5 express lanes which might provide buses with easier access to the downtown bus tunnel.

Less obvious, but equally serious, are the difficult connections encountered by transit riders whose destinations are the University of Washington, University District, and other activity centers west and east of Lake Washington. Some bus routes from the eastside exit at Montlake, while others discharge passengers at a freeway flyer stop at Montlake. In both cases, travelers must take buses that cross the often-congested Montlake Bridge. Not only does this increase bus travel times from the east side of Lake Washington to the University, riders on a major cross-Seattle route, 43/44, which crosses the bridge experience unreliable service. Travelers making connections from I-5 express buses originating in north King County and south Snohomish County who are heading for destinations on the east side of Lake Washington face a difficult and unpredictable transfer through the University District or a longer trip with a transfer in Downtown Seattle. The consequence of this bottleneck is a low level of transit ridership on a very heavily used corridor.

Barriers to Non-Motorized Travel on SR 520

The Evergreen Point Bridge and the SR 520 corridor were built without a bicycle or pedestrian lane. A recent study indicated that a bicycle/pedestrian lane could be added to the existing bridge. If this were done, a more direct bicycle connection might also be added between Montlake with Eastlake to make bicycle commuting feasible from east of the lake to the Seattle CBD.

II. Public-Private Transportation Initiatives Program Proposal

In 1993 the Washington Legislature passed the "New Partners" program which allows the state to negotiate contracts with private entities who wish to build transportation projects on the state transportation system. This law authorizes a private entity to charge tolls to cover the cost of construction, operation and maintenance, and to earn a reasonable profit. In May of 1994, a proposal was made by Washington Transportation Partners, a consortium of Morrison Knudsen and Parsons Brinkerhoff, to apply tolls to SR 520 for the purpose of expanding the capacity of the corridor and making a number of improvements. The Washington State Transportation Commission decided in August 1994 to enter into negotiations with Washington Transportation Partners.

Washington Transportation Partners proposes to address the problems of the SR 520 corridor in two phases. Phase One would involve seismic strengthening of elevated freeway structures and the connection of SR 520 to the I-5 express lanes. Phase Two would involve expansion of SR 520 capacity by two lanes, one in each direction, for buses and 3-person carpools. A bicycle pedestrian lane and wider shoulders would also be added. Three lids over SR 520 and I-5 in the Montlake and Roanoke areas would be built and capped with parks.

This proposal sparked considerable controversy on both ends of the SR 520 corridor, and contributed to calls for the repeal or substantial modification of the legislation establishing the public-private partnership program. Several Seattle neighborhood organizations and the city councils of the "Points" communities (Hunts Point, Medina, and Yarrow Point) have voted to oppose the project. Currently (January, 1997) this proposal is on the shelf.

Some groups have voiced particular opposition to tolls. As a matter of historical note, tolls were in place on the SR 520 crossing of Lake Washington from 1963 to 1979. State law, then and now, allows the state to charge tolls for the purpose of paying the costs of construction and maintenance of a bridge, tunnel or limited access highway. The law does not expressly authorize the state to charge tolls for the purpose of managing traffic volume.

III. A potential "win-win" alternative


We propose that growth of travel demand on the SR 520 crossing of Lake Washington be managed using congestion pricing. The number of vehicle lanes would not be increased, even if the bridge were to be replaced. Tolls would be applied to SOVs and commercial vehicles using SR 520 to create free flow conditions, and the toll revenues would be used to fund a range of improvements in the corridor: increased transit service, noise barriers and lids, quieter roadway surfacing, seismic strengthening, control of auto-generated water pollution, a bike/pedestrian lane crossing Lake Washington, a more direct bike route from Montlake to Eastlake, a transit and HOV connection from 520 to I-5, and a PRT system connecting 520 and I-5 via the University District. An optional measure would be removal of the unfinished freeway ramps. The SR 520 and I-90 corridors would be operated as one cross-lake system and, if needed, tolls would also be applied to I-90. Although one or the other bridge is the crossing of convenience for a fraction of all drivers, depending on their origin and destination, the two bridges are close enough to each other (four miles) to work as a unit. For example, more than half of westbound weekday traffic on SR 520 continues southbound on I-5 toward the Seattle CBD and I-90. A study of cross-lake travel patterns found that more than 70 percent of the trips in both directions were either best served by I-90 or could use that crossing without significant inconvenience. Some drivers in the latter category may already have switched from SR 520 to I-90

A Strategy for the University District: A PRT Circulator

The University District would seem an ideal location for a personal rapid transit (PRT) system to move commuters efficiently from the a transit center for express buses on NE 45th Street at I-5 to destinations at and around the University District and UW Campus, and to provide similar connections at a transit center serving SR 520. The latter would require a high level bridge across the Montlake Cut that met aesthetic standards and community expectations. The system would also serve as a circulator for internal trips within the U-District. It might also be extended eventually to University Village and Children's Hospital.

PRT systems characteristically involve small (one to four passenger) automated, electric-powered vehicles that are suspended from or run on elevated guideways. Computers control the movements of the vehicles to maximize system efficiency.

A University District PRT network layout has been sketched out by Schneider. This 7-mile (one-way) network would have 16 stations in addition to two interchange facilities, one at I-5 and the other at SR 520. Stations would sited along 15th NE to serve the main (north) campus. The system would have a loop with four stations serving the medical complex on the south campus. Additional stations would serve the residential / commercial neighborhood west of the campus and east of I-5.

A PRT system is designed as a "smart" system. Passengers choose their destinations among the stations on the network of guideways, and the vehicle takes them directly there by the shortest route - without and intermediate stops.

In addition to PRT, several other elevated transit technologies could be used to serve the University District.

Estimate of costs and toll revenues

Sufficient data exist to roughly estimate the costs and benefits of this alternative proposal. We assume that the project will be one continuous effort without phases, and that toll revenues will not be used to expand the capacity of the SR 520 corridor. If the private entity declines to negotiate the project without added capacity, the state would proceed to apply tolls and carry out the project as outlined below. This would require state legislation.

We assume that tolls will be applied initially to SR 520. We base our toll revenue assumptions on the estimates of Vollmer & Associates. We assume a toll of $1.00 in each direction for a passenger car, with a surcharge of 50 cents in AM and PM peak periods. HOVs with 3+ passengers will pay 50 cents at all times. Users of electronic debit cards that can be read automatically will receive a 25 percent discount. Toll rates will be increased in step with inflation. With these rate assumptions, tolls will generate about $30 million annually. If toll revenues should exceed the amount needed for the projects described below, they will be used for additional transit improvements and environmental mitigation efforts.

Toll revenues will be used to increase transit service to meet expected transit demand resulting from congestion pricing, to construct a bicycle/pedestrian lane addition to the existing SR 520 bridge, to improve bicycle travel from Montlake to Eastlake, to construct noise barriers on and lids over SR 520 and I-5, to construct a transit and HOV connection between SR 520 and I-5, and to construct and operate systems to collect and treat storm water run-off from SR 520 that currently is drained into Lake Washington, Union Bay, Portage Bay, and Fairweather Bay. Rough "back of the envelope" estimates of costs for some of these items plus operating expenses for toll collection and profit are shown in the table below.

Cost Estimates for Various Capital Facilities and Operating Activities

Noise barriers and lids $286 million
Expanded transit service $19 million/year
Improved Connections to Interstate 5 $10 million
Construction of U-Dist. PRT System $105 million
Seismic upgrade $15 million
Biking/walking lane $14 million
Water collection/treatment $20 million; $2 million/year
Construction of toll plaza $7 million
Toll collection expenses @10% $3 million/year
Reasonable profit @ 10% $3 million/year

We have arbitrarily assumed that weekday transit service would double with the advent of tolls. Spring 1994 estimated weekday transit ridership across the SR 520 bridge was 11,100. After tolls it would be 22,200. Using Metro Transit's total cost subsidy for an average bus ride (approximately $6.70), the annual cost of providing expanded transit service would be 11,100 x $6.70 x 260 = $19.3 m. We have not estimated the cost of operating the PRT system.

Estimate of Benefits

Tolls and congestion surcharges would reduce travel delay on the SR 520 corridor for SOV, HOV, and transit passengers, and would increase the mode share of HOVs and transit. The bike/pedestrian lane would increase the share of non-motorized travel. Construction of the surface water system would reduce the external costs associated with water pollution.

For the purpose of this cursory analysis, we estimate only the benefits resulting from the reduction in delay due to recurring congestion and one-half of the nonrecurring congestion. The SR 520 crossing is one of the most congested corridors in the region. We assume that it accounts for 10 percent of the total regional congestion delay. We use the Texas Transportation Institute's most recent (1991) estimate of vehicle hours of delay under heavy and severe traffic conditions. The total vehicle hours of delay on the SR 520 crossing for 1990 was 32.7 million. We estimate that tolls and congestion pricing would achieve this magnitude of benefits. Including the value of fuel saved, the benefit would be approximately $50 million per year.

IV. Approach to the Analysis of this Alternative

There are several prerequisites to the translation of this proposal from a suggestion to a viable alternative: 1) the efficacy of congestion pricing as an important potential travel demand tool for this region must be articulated; 2) the interest of the any private sectors partner(s), WashDOT, PSRC, affected cities, and key community leaders in a negotiated "win-win" solution must be clearly indicated; 3) a community discussion/consensus building exercise around a broad range of alternatives must be mounted; and 4) much better data describing the likely effects of transit improvements on transit ridership, the effect of tolls on transit mode share, the shift of drivers from SR 520 to I-90, the social equity of tolls and the impact of regional measures to manage transportation demand must be developed..

Once these steps have been taken or are underway, a least/full cost analysis of alternative proposals could be employed to assist the process of developing a preferred alternative. The least/full cost methodology and model developed by the research team associated with the ITE would be available for this analysis.

V. Elements of the Least/Full Cost Analysis

The least/full cost methodology would be applied to a set of alternatives for the SR 520 and I-90 corridors, which might include (1) a trend scenario in which congestion is allowed to increase at anticipated rates; (2) the proposal set forth by Washington Transportation Partners (WTP) involving congestion pricing and the construction of additional bus/HOV lanes; (3) the alternative set forth in this paper that would modify the WTP proposal by excluding the construction of new highway capacity and fund more transportation alternatives and environmental mitigation; and (4) alternatives resulting from the public involvement process.

The entire ITE model would be implemented including its travel demand components. These would be combined with the full costing capability to compare total market and non-market costs under each of the alternatives. The objective of this analysis would be to compare and rank social costs associated with each of these alternatives and ultimately to recommend a course of action for the SR 520 corridor.

VI. Conclusions

1) The SR 520 corridor is in need of a comprehensive solution that involves transit, non-motorized improvements, and environmental mitigation.

2) Tolls may be the key to improving traffic flow, reducing some of the impacts of vehicle travel on neighborhoods in the corridor, and generating revenue to pay for enhanced transit, non-motorized improvements, and environmental mitigation.

3) A proposal advanced by Washington Transportation Partners under the state's public-private partnership program, which recommends expanding lane capacity in the corridor, has not succeeded in gaining sufficient support in impacted communities and therefore needs to be modified..

4) The program for SR 520 should be restructured to encompass a wider range of alternatives and a search for a "win-win" solution.

5) Least/full cost planning would assist efforts to discover a preferred alternative.


S. J. Hallett, A New Approach to Getting Around, Pathfinder Rapid Transit, 1994.

METRO Transit Ridership Across I-90 and SR-520 Bridges, Private communication from Erin Laine, Metro Marketing and Strategy Division. August 29, 1994.

D. Nelson and D. Shakow, Applying Least Cost Planning to Puget Sound Regional Transportation, Phase I Report, Institute for Transportation and the Environment, February 1994.

D. Nelson and D. Shakow, Applying Least Cost Planning to Puget Sound Regional Transportation, Phase II Report, Institute for Transportation and the Environment, December 1994.

Points Communities (SR 520) Citizen's Review Committee. Damage to Eastside Ecosystem by the proposed SR 520 Corridor Improvement Program, Letter to the Washington State Transportation Commission, August 12, 1994.

Regional Transit Project, Final EIS: Volume 1, March 1993.

J. B. Schneider. Private communication, October 1994.

D. L. Shank, S. M. Turner, and T. J. Lomax, Trends in Urban Roadway Congestion -- 1982 to 1991 , Research Report 1131-6, Texas Transportation Institute, September 1994.

Vollmer Associates, Washington State Public & Private Initiative: Project Route 520 Potential Toll Revenues, 1994.

WSDOT, Ramp and Roadway Traffic Volumes: I-5, I-90, SR 520 etc. Summary Report 1992.

WSDOT, SR 520/I-5 Noise Study. Report prepared by Towne, Richards & Chaudiere, Inc. 2nd Draft. March 1993.

Washington Transportation Partners, Inc. SR 520 Corridor Improvement Program, Proposal to the WSDOT, May 1994.

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Last modified: January 25, 1997