II. Summary of Major Findings and Recommendations Background The Problem The principal problem consisted of westbound vehicles in the George Hopper corridor regularly creating queues extending to Burlington Boulevard. The source of this problem movement appeared to be lack of capacity in the westbound to southbound left turn access to the I-5 southbound on-ramp. To address this deficiency the City and WSDOT agreed to study a conceptual solution consisting of a westbound double-lane left turn to the I-5 southbound on-ramp which in turn would necessitate a one lane widening of the existing bridge and approaches. Traffic mitigation fees To assist with funding of the above cited improvement, the City with the assistance of this consultant developed a traffic mitigation fee model for all new development that might send traffic to George Hopper Road. The currently adopted fee structure should raise up to $1.6 million based on the 2012 land use estimates. Steering Committee A consultant was selected to assist with scoping and conduct of the study. A steering committee to guide the effort consisted of representatives from WSDOT, Skagit County and the City of Burlington. The steering committee met once in January 2004 to set parameters for the scope, participated in scope correspondence in February, and then met to review study products in June, October, December, and February 2006. Study Objectives The study objectives consisted of identification of geometric features (and costs) needed for acceptable future traffic operations of the I-5/George Hopper Road interchange and arterial corridor. Study results were to be used to search for and secure funding and establish parameters for subsequent Design Report, PS&E and Construction. Future Traffic Volumes Future year traffic volumes were developed for a short range and a long range horizon year analysis. For this study, the short range year was determined to be 2020, and 2030 was used for the long-range horizon year Area Growth It is estimated that the Burlington and Mt Vernon area will grow in total vehicle trips by approximately 50% over the next 16 years (through 2020). However, between 2020 and 2030, it is estimated that total vehicle trips in Burlington will only grow approximately 10% due to saturation of available land in the earlier period. Burlington increases at a rate of 3% per year to 2020 and then slows down through 2030. Over the course of 26 years, the Burlington growth averages some 2% per year I-5 Volumes I-5 traffic volumes as measured at the Skagit River (bothways) are estimated to increase approximately 34% between 2004 and 2020. By 2030, with an assumed eight lanes across the Skagit River, the resultant increase in volume on I-5 from 2020 to 2030 is approximately 30% over that ten year period. Selected Corridor Options A selection of the best performing corridor options analyzed are given in the following line drawings on an aerial base map to visually familiarize the reader with the local land use relationships. The selected options for 2020 are 3A, 4D, and 4E. For 2030 the options are 4B, 4D, 4E, and 4F. In addition to the corridor options, a proposal was forwarded by WSDOT early in the analysis process to consider a Cascade Mall/Costco frontage road concept and that has been included in practically all of the analyses in either the form of an internal road connecting via existing Costco Drive or via a direct connection to George Hopper Road using a portion of the converted northbound on-ramp (see Figure 2.4a and 2.4b). 
Operational Analysis Future 2020 and 2030 PM peak hour level of service, delay, and 95th percentile directional queue information are shown on the attached table for the best performing options. All of the intersections are estimated to operate at an acceptable LOS D or better. However, the queuing along George Hopper Road between Burlington Boulevard and Bouslog Road is estimated to be problematic at certain locations for many of the discarded options. 2020 In this 2020 evaluation there are three clearly best operating options (80 to 83 hours of delay) each of which has no queuing problems: - 3A, Northside loop ramps; (80 hours of delay)
- 4E, NW quadrant trumpet loop ramp with eastside widening of G. Hopper Road; (83 hours of delay). This is the recommended 2020 plan.
- 4D, NW quadrant trumpet loop ramp with 5-leg roundabout on eastside and Cascade Mall/Costco frontage road connection; (83 hours of delay).
2030 In this 2030 evaluation summary there are four options to consider. In order of least delay, the best performing options are as follows: - 4E, Northside loop ramps with slip ramp from NE loop to new Cascade Mall/Costco frontage road and relocated NB on-ramp intersection; (80 hours of delay)
- 4D, NW quadrant loop ramp with 5-leg roundabout on eastside including Cascade Mall/Costco frontage road connection and new NB on-ramp, plus NB off-ramp underpass of G Hopper (for NB to WB traffic) and new NB on-ramp to intersection with Mall frontage road; (86 hours of delay).
- 4F, NW quadrant loop plus 5-leg, partial 3-lane roundabout with new Mall frontage road and G Hopper Road widened by one lane to the east; (89 hours of delay). This is the option that has been selected as the preferred 2030 plan for its ability to perform and accommodate the proposed frontage road at the least probable cost.
- 4B, NW quadrant loop ramp with 1-lane widening of G. Hopper Road between Burlington Blvd and NB on-ramp – the 2020 plan plus widened I-5; (101 hours of delay).
Since Option 4B does not include the mall frontage road concept, it is not proposed for the recommended plan although it costs practically nothing in 2030 having been essentially constructed as the 2020 plan. However, should subsequent evaluation find the frontage road and/or the roundabout concept infeasible, this option would be the logical choice. Planning and Design Issues SB on-ramp limitations The initial concept solution to address the existing westbound queuing problem assumed a westbound double left-turn lane access to the southbound on-ramp which included thus a one lane widening of the existing three-lane George Hopper bridge. However mid-study direction from the steering committee indicated that the double left-turn lane discharge with its merge on the on-ramp would not be allowed under the existing I-5 mainline condition as it was contributing too much platooned traffic with deleterious mainline operations affects. Clearances and Constructability A loop concept was proposed to avoid the platooned traffic impacts of the westbound double left-turn lane solution. This concept also offered the significant advantage of relative permanence unless the future I-5 were to overpass George Hopper Road, which is considered highly unlikely, or the mainline grade were to be raised significantly. NW Quadrant Loop plus Existing On-ramp An initial loop design was prepared that utilized a barrier protected collector-distributor road design to collect the loop traffic along with the eastbound to southbound right turning traffic. This concept however had two serious deviation requirements: 1) length for acceleration and merge was short some 325 feet at the Skagit River bridge abutment and 2) the lateral clearance under the George Hopper bridge was deficient some five to six feet. NW Quadrant Trumpet Loop A so-called trumpet loop design alternative utilizing a "Parallel Type On-Connection" was prepared that comfortably met both the required length for acceleration and merge design standard and the lateral clearance design standard with a modest height retaining wall. This design requires southbound on-ramp traffic from the west to turn left on a slip ramp and enter the loop and the existing southbound on-ramp would then be barricaded. Future Mainline Widening There is 18 feet of horizontal clearance between the edge of the inside southbound mainline lane and the bridge abutment which provides thus the minimum clearance needed for widening the freeway by one lane on the median side. However, the Skagit River bridge reconstruction approach method will be the determining factor on this issue with decisions expected in the upcoming Skagit County I-5 Corridor Study. NW Quadrant Loop Design R/W Take Under the worse case, which is an outside mainline widening scenario, the R/W take is 113,000 square feet from private ownership and 2000 square feet from the City. It is believed that a median side widening is the more likely scenario, however a worse case take may be the prudent approach in absence of knowledge of an I-5 design solution. Fortunately, the land required is currently undeveloped. SB Off-ramp Clearances to Goldenrod Road and Gages Slough The closest the NW quadrant loop design off-ramp edge of shoulder comes to the Goldenrod Road curb line is 16 feet at the existing angle point in Goldenrod Road. This distance should allow sufficient space for a drainage ditch and a barrier with headlight glare screen. If however I-5 were to be widened on the outside by one lane as has been suggested the distance shrinks to four feet and thus Goldenrod Road would have to be shifted westward over about a 300 foot length. George Hopper Bridge Widening Vertical Clearance One of the early constructability issues was the question whether the bridge could be widened while maintaining cross slope and still meet vertical clearance to I-5. Structural review indicated the widening could be readily accomplished with shallower girders thus eliminating any vertical clearance issues. Skagit River Dike Move The project scope assumed a long range scenario of an I-5 widening and new 8-lane river structure prior to 2030. That event was expected to raise the profile of the mainline to accommodate moving the existing dike and Whitmarsh Road some 300 feet north. It was expected during scoping of the study that the profile change would extend past the existing G Hopper bridge and would thus require replacement of that structure and its ramp connections. The study found, however, that the move does not extend the necessary profile changes sufficiently to impact the George Hopper bridge. There is more than adequate distance for stopping and decision sight distance. 100 Year Flood Plain Issue The study section of I-5 is marginally below (one or two feet) the current FEMA definition of 100 year flood elevation. The dike district has been purchasing property in the corridor for dike moves that would expand the flood handling capacity of the river and theoretically lower the 100 year flood elevation. In addition negotiations for improved Skagit system flood storage management have been ongoing with congressional representative input. It is expected that flood storage management combined with dike moves will be productive and actually result in lowering the current official estimate of 100 year flood elevation. In this case the I-5 mainline should not have to be raised and thus the existing George Hopper bridge may remain subject only to seismic issues of obsolescence or mainline centerline relocation. Selected Design Alternatives 2010 Interim Design Suggestion A roundabout design alternative for the NW quadrant loop option on the west side of the freeway was proposed to provide more immediate relief for the queuing of WB left-turn traffic at the I-5 SB ramps under the assumption that funding for the loop solution is a number of years in the future. This plan would also include a westbound one-lane widening of George Hopper Road from Burlington Boulevard to the I-5 bridge pavement seat. Figure 2.1 depicts the proposed plan. In addition a sidewalk (undepicted) should be added to the south side of the bridge and continued as shoulder on either side. The roundabout is estimated to operate quite satisfactorily (LOS B) for some fifteen years or possibly less. The estimated cost for this plan concept including the eastside George Hopper widening is $1.8 million. It should be noted that the roundabout design would not be useable with the longer range loop ramp installation unless the roundabout and thus the ramp alignments were moved west to the trumpet intersection location. This action would require construction of the new off-ramp in the loop location and at that point the economic argument breaks down since the roundabout construction cost is substantially higher than the signalized intersection portion of the loop ramp design 2020 Recommended Plan The NW quadrant trumpet type loop ramp combined with the George Hopper widening from Burlington Boulevard to the NB on-ramp has been selected as the recommended plan for the 2020 design year. The total cost for this plan is $6.6 million which assumes the eastside George Hopper one lane westbound widening ($0.7 million) is accomplished earlier as part of the 2010 plan or independently. The plan is depicted on Figure 2.2. Westside The NW quadrant loop itself is also recommended for the 2030 or long range plan thus implementation action should be considered an investment with a substantial design life. Eastside Similarly, the eastside George Hopper one lane westbound widening is common to a number of 2030 leading candidate plans so it too is potentially a long term investment. 2030 Recommended Plan The NW quadrant loop option on the west side of the freeway combined with an eastside five-leg roundabout including a portion with three lanes and the Mall/Costco frontage road connection has been selected as the preferred 2030 Plan. Refer to Figure 2.3. 
Westside This plan requires simple and economical construction revisions to the trumpet loop design. The trumpet design presumably will have been constructed some years prior as part of the 2020 plan. For 2030 the trumpet feature (EB to SB on movement slip ramp) would be eliminated and the barricade of the existing southbound on-ramp removed to restore the EB to SB movement to that ramp. This is possible since I-5 is assumed to have an auxiliary lane commencing at the George Hopper on-ramp and extending to at least the next interchange south (College Avenue). Eastside The five-leg roundabout appears to be the simplest solution for the complicated geometry required to incorporate the Mall/Costco frontage road connection with its attendant benefits to George Hopper Road and Burlington Boulevard operations. The ultimate decision for this option might be subject to state and national operational experience with high volume roundabouts and particularly those with portions involving three-lane sections. The George Hopper Road westbound one-lane widening is also applicable to this option extending from Burlington Boulevard to the roundabout. However, the Costco driveway operation changes significantly with southbound operation limited to right-turns-out and no left-turns-in. The estimated cost for the five leg roundabout is $2.4 million which does not include costs for the Costco property roundabout and internal frontage road to Cascade Mall which will be substantial – in excess of $3.0 million for crossing Gages Slough based on the Goldenrod bridge cost.
|
