Arboretum Bypass Plan (aka Union Bay Alternative)
by Craig Dalby craigdalby@hotmail.com

Overview

The Arboretum Bypass Plan is a new alternative route for part of SR 520, specifically dealing with the Evergreen Point Bridge approach between Portage Bay and Lake Washington. It appears that this option has not yet been considered in the Environmental Impact Statement process. Furthermore, this plan seems to meet the requirements for a prudent and feasible alternative, and should be included as a new, fully-developed alternative in a Supplemental Draft EIS.

Description

This is a conceptual plan at present, showing a route that would restore the Arboretum and improve transportation linkages without heavily impacting neighborhoods and the salmon run through the area. It does not specify a particular number of lanes, and the exact layout of ramps is subject to modification.
Briefly, the route is as follows. From the Eastside, the floating section of the bridge would head to the opening to Union Bay midway between Madison Park to the south and Laurelhurst to the north. The floating section would rise gently on its western end, then give way to a section on pilings which would rise to a high bridge across the ship channel. The route then would drop slowly over Union Bay, again on pilings, to the shore just northeast of Husky Stadium. Here a future light rail line could split off and join up with the north-south line to be built from Capitol Hill to the stadium station. Also, two ramps for buses and vehicles would run on the surface (or potentially underground) to the Pacific Street - Montlake Boulevard intersection. The main freeway would proceed underground through a tunnel under the Montlake Cut and would emerge along the current freeway alignment near Portage Bay. Ramps would connect from Montlake Boulevard to the freeway to the west. Additional ramps connecting Montlake Boulevard to and from the tunnel side of the freeway could be constructed if needed.
One possible lane configuration would have two general purpose lanes and one HOV lane in each direction, plus shoulders and a bike/pedestrian lane, over the main bridge. The HOV lane in each direction and the bike/pedestrian lane would peel off from the main freeway at Husky Stadium. The main freeway would continue through the tunnel and over Portage Bay to Interstate 5 with two general purpose lanes in each direction, plus shoulders. If access to and from the Capitol Hill area is needed on the south side of the Montlake Cut, ramps could be added at the west end of the tunnel. One ramp from northbound Montlake Boulevard could enter the tunnel eastbound, and another ramp could exit the tunnel and connect to Montlake Boulevard southbound.
Another possible configuration would carry all six lanes mentioned above, including the HOV lanes, through the tunnel and over Portage Bay to Interstate 5. It would also be possible to have both HOV and general purpose lanes on the ramps to and from the Husky Stadium area. Determining the optimal configuration would require cost estimates for the various options.
All curves and grades needed to construct the route as depicted on the accompanying maps should meet or exceed state engineering specifications. That said, the state may want to adjust some features to provide a greater degree of safety or for other considerations. For example, the tunnel could be lengthened to reduce the grade below 5%, and the radius of the curve leading to the tunnel from the Union Bay could be increased. It should be noted, however, that the curve over Union Bay has approximately a 1700 foot radius, which is considerably greater than the approximately 1000 foot radius on Interstate 90 around the north side of Beacon Hill.

Purpose

The main objectives of this alignment for SR520 fall into several categories:

 

            Transportation

The Arboretum Bypass Plan offers a way to reconcile differences between residents from the Eastside and Seattle over how wide the freeway should be. The main Evergreen Point Bridge could, for example, be designed with the six-lane option without damaging the Arboretum. The HOV lanes could, potentially, peel off from the main freeway at Husky Stadium, leaving two lanes to continue through the tunnel and over the Portage Bay Bridge. This is just one of many permutations of the plan, however.

Under any of the current WSDOT proposals light rail will be effectively precluded from this corridor. An east-west light rail line following the freeway route up to, or through, the Arboretum would have to get to the Husky Stadium station via high bridge or tunnel. The high bridge route would further damage the Arboretum and surrounding wetlands, and probably couldn’t be built with a steep enough grade to get underground on the University side of the Montlake Cut. A tunnel route under the ship channel, on the other hand, would be subject to the same cost and environmental problems that WSDOT found prevented them from considering the tube-tunnel proposal for the freeway.

The Arboretum Bypass Plan allows for better transportation connections from the Eastside than any of the current proposals, including the Pacific Interchange option. If bus rapid transit is selected, at least initially, for this corridor buses could exit at Husky Stadium, drop off passengers who would then transfer to light rail to head downtown. The buses would then pick up eastbound passengers and head back over the bridge. This arrangement would reduce the number of buses traveling through Seattle’s central business district, increase ridership on the north-south light rail line, and provide a faster commute between the Eastside, the University, and downtown.
When light rail is eventually added it could replace the HOV lane. Where it splits off at the west edge of Husky Stadium it could drop underground to meet up with the planned north-south light rail line at the stadium station. The east-west line could then continue elsewhere, perhaps to Ballard, since the 45th Street corridor has been studied as an area that would benefit from rapid transit.

The Arboretum Bypass Plan will most likely lead to a large reduction in traffic through the Arboretum. This is because the plan removes the Lake Washington Boulevard ramps, while keeping the main interchanges on Montlake Boulevard, a four-lane street with a 30-35 MPH speed limit and the principal north-south arterial in the area. Ramps to and from the east could be added at the present Montlake Interchange site if they are needed to ease traffic flows to and from neighborhoods south of the freeway. The Pacific Interchange option, by contrast, puts all traffic to and from the south side of the freeway through the Arboretum via Lake Washington Boulevard, a winding, two-lane, park road with a 25 MPH speed limit.

 

Environment

The Arboretum Bypass Plan restores the Arboretum to its pre-1960 appearance. No Arboretum plant specimens are damaged, and the existing freeway is removed from the landscape. Cultural sites on Foster Island are not impacted.

According to the National Marine Fisheries Service, the most crucial zone in this area of the Lake Washington salmon migration route is at and around the Montlake Cut. This is because all the fish must pass through there. The Arboretum Bypass Plan avoids any construction in this zone, except the tunnel under the Montlake Cut. The tunnel, however, is bored deeply enough to avoid any disturbance to the ship canal, and, therefore, to the fish.

The Arboretum Bypass Plan impacts a smaller area of wetlands (near Husky Stadium) than any current WSDOT alternative. In addition, wetlands in and around the Arboretum are restored to their pre-1960 state.

If a stormwater treatment area is deemed necessary for the Union Bay section of the freeway, such a facility could possibly be placed just north of the east entrance to the tunnel as shown on the accompanying maps.

Improved transit connections, especially rapid transit in the form of light rail, will be an essential component in reducing greenhouse gasses in the coming decades. Rapid mass transit will also support higher development densities mandated under the Growth Management Act.

 

            Recreation

The north end of the Arboretum, including the waterfront trail, is vastly improved for recreational uses over the current condition or any of the current WSDOT alternatives. The absence of any overhead structures and resultant shading from such structures greatly enhances the visitor’s experience.

McCurdy Park is significantly improved over the current condition or any of the current WSDOT alternatives.

WSDOT land near the Arboretum could be converted to park use with no freeway ramps intruding on the landscape.

The former freeway corridor from Montlake Boulevard eastward to the water’s edge just south of McCurdy Park could be converted to park use.

 

            Neighborhoods/University

Visual impacts to the Montlake neighborhood under the Arboretum Bypass Plan are less than in any current WSDOT alternative. Noise impacts to the Montlake neighborhood would likely be reduced from current levels, as a good deal of traffic would be redirected away from the present Montlake Interchange.

Visual and noise impacts of the Arboretum Bypass Plan are essentially evenly split between Madison Park and Laurelhurst, with neighborhoods on neither side of Union Bay bearing a disproportionate burden.

The Arboretum Bypass Plan minimizes the impacts to properties owned or managed by the University. While the ramps to and from the Pacific Street – Montlake Boulevard intersection near the stadium may have a larger footprint than the ramps planned under the Pacific Interchange option, they would allow more flexibility for the University’s future building plans, because they would be on the surface or underground. Some additional University property would probably be required for stormwater treatment and a tunnel ventilation system. This latter feature might be constructed near the climbing rock and could potentially be integrated with that structure.

 

Cost

While there are no cost estimates included with this proposal, it should be noted that the Arboretum Bypass Plan offers the potential for a substantial cost saving in future years if light rail is placed in this corridor. The cost saving would result from not having to construct a separate bridge or tunnel to get a light rail line from the Arboretum area to the north side of the Montlake Cut where the east-west line could meet up with the north-south line at the stadium station. At the least, the cost of the tunnel in the Arboretum Bypass Plan can be viewed as a down-payment on a light rail line along the SR520 corridor.