chapter 3 minnesota th 36/th 95 interchange 3.pdfinterchange (figure 3.2). as a result of the...

St. Croix River Crossing Project - Visual Quality Manual

Minnesota Department of TransportationWisconsin Department of Transportation

3-1

chapter 3

Minnesota TH 36/TH 95 Interchange3.1 Context – Existing TH 36/TH 95 Environment

The proposed TH 36/TH 95 interchange will occupy a large area of land a few hundred feet west of the St. Croix River and 1.5 miles south of downtown Stillwater. TH 36 will pass over TH 95 at this new interchange, which will be located at the west end of the new river bridge. Trunk Highway 36 on the west side of TH 95 will be on fill, while TH 36 and ramps on the east side of TH 95 will be elevated on structure. Portions of the on ramp and off ramp west of TH 95 will be in cut sections. TH 95 accesses Stillwater to the north of the interchange and the cities of Bayport and Oak Park Heights to the south. A series of stormwater treatment ponds will be located at the interchange to receive run-off from the roadways.

Various types of development occur in the vicinity of the TH 36/TH 95 interchange. The area directly northeast of the interchange is occupied by a sewage treatment plant and a marina/condominium complex. Southeast of the interchange, an Xcel Energy coal-fired generating plant occupies a large tract of land along the river (Figure 3.1). A residential neighborhood overlooks the interchange site from high ground to the northwest, and another residential area occupies high ground to the southwest. The interchange will be in the visual panorama of the historic St. Croix Overlook, which is situated about one third of a mile north of the interchange (Figure 3.2). As a result of the interchange location, motorists traveling TH 36 and TH 95 will have views of the sewage treatment plant and the gen-erating plant, and residents in areas to the northwest and southwest will overlook the new roads and ramps.

East of Osgood Avenue on TH 36 approaching the location of the planned TH 36/TH 95 interchange, the landscape character of the river valley begins to emerge. The existing TH 36 curves into TH 95, which

figure 3.1Xcel Energy’s King Generating Plant

figure 3.2St. Croix Overlook



3-2

chapter 3 Minnesota TH 36/TH 95 Interchange

river terrace area where the proposed TH 36/TH 95 interchange will be constructed. Dense tree and shrub vegetation, however, still occupies the steep slopes, the base and the top of rock bluffs, and the margins of land between roads, railroads, and developed areas. Both sides of existing TH 95 are lined by deciduous trees and shrubs, which screen views of the sewage treatment plant, Sunnyside Marina, and generating plant (Figure 3.3). Roadsides along TH 95 have been described as “leafy and green” and lightly wooded, making for an attractive approach to the City of Stillwater. Bottom-land trees and shrubs are common on the riverbank and lower terrace over which the new bridge approach will pass. On the west side of TH 95, a residential area that was cleared of homes in 1995 for construction is well shaded by upper story deciduous trees. Although the tree and shrub cover is fragmented over this river terrace landscape, the visual effect approximates that of a wooded terrain.

figure 3.3Vegetation Screens Views along TH 95

continues north to the Stillwater Historic District and the Lift Bridge. The curve clearly marks the transi-tion from the TH 36 commercial area to the scenic St. Croix River Valley. The VQRC emphasized the natu-ral features of this transitional area, including stone outcroppings and wooded areas. Some of the industrial development south of TH 36 and east of TH 95 was considered a negative aesthetic influence (these fea-tures include the regional wastewater treatment plant, the generating plant, and a State Prison). However, except for the generating plant chimney, these elements are fairly well screened by trees and so are not easily seen. Proceeding north along TH 95 into Stillwater, there is no clear entry statement into the city, but the Historic District soon becomes evident, beginning with the “caves” business area where building architecture is integrated with natural sandstone outcroppings. The balance of the downtown business district appears one or two blocks further north.

The interchange will be developed on terrain made up of a series of slopes and terraces stepping up from the river. From a review of plant guides and by observing existing terrain features, the river terraces along the St. Croix were once characterized by diverse plant com-munities tied to a varied geology. Low-lying benches and bottomlands in the floodplain contained emergent marshes, bogs, “prairie bottom” or “wet prairie,” flood-plain forest, and hardwood swamps. Intermediate and upper level terraces further from the river consisted of flat and gradually sloping ground, steep slopes and rocky bluffs between terraces, as well as ravines, seeps, and depressions. The larger flatter terraces may have been vegetated by prairie or oak savanna, but the steep slopes, ravines, seeps, and many terraces would likely have been covered by deciduous forest. Especially east facing slopes, which tend to stay shaded and moist, would have been dominated by forest.

Human activity and development have eliminated much of the pre-settlement forest vegetation on the



3-3


Views to the river from the St. Croix Overlook are across treetops and foliage which largely obstruct the visual clutter of roads and development between the overlook and the river (Figure 3.4). A more thorough description of the overlook and its reconstruction is included in Chapter 8, Historical/Cultural Resources. Similarly, views from the river of the area that will be occupied by the interchange are of mostly trees. Views from residential areas above the proposed interchange are of what appears to be a tree covered landscape. Preservation of viewshed and visual quality from the overlook, river, and residential neighborhoods on the bluffs above the proposed interchange are an important consideration in the design of the interchange. The Na-tional Park Service and Minnesota State Historic Pres-ervation Office have indicated that adverse impacts to views from the overlook and river are to be avoided to the greatest extent possible and, where adverse impacts are unavoidable, they be minimized and mitigated.

A considerable amount of vegetation will be removed for construction of the TH 36/TH 95 interchange, its stormwater ponds, and structures. This vegetation currently screens a variety of man-made elements, and contributes to the semblance of a leafy and green land-scape from various vantage points. Removal of these pockets and curtains of foliage will make the existing man-made elements and the new construction more visible. The character and quality of views from several locations, including from TH 36 and TH 95, will be sig-nificantly altered by construction of the new highway interchange. It is therefore important to reestablish the pockets and curtains of foliage to screen and attenuate the views in this area.

3.2 Evaluation Criteria and Guidance

Input from the VQRC shaped the following evaluation criteria and goals for the TH 36/TH 95 interchange area:

• Maintain the sense of forested or wooded landscape

• Create a clear entry statement for Stillwater, extend-ing north from the interchange along TH 95

• Screen the negative visual features (nearby indus-trial development)

• Narrow the visual field and manage traffic/speed (the interchange will include two intersections along TH 95 for the ramps connecting to TH 36 and the new river bridge)

figure 3.4View East to River from St. Croix Overlook



3-4


3.3 Recommendations

To maintain the wooded visual character of the TH 36/TH 95 interchange area landscape, open ground areas associated with the interchange should be densely planted with native trees and shrubs between and along roads and ramps (Figures 3.5, 3.6, and 3.7). Over time, this vegetation will attain sufficient height and density to visually screen many of the interchange features from the St. Croix Overlook, the river, and adjacent neighborhoods. Moreover, this restored vegetation will return a wooded character to the TH 95 corridor and will reduce the openness and scale of the interchange (Figures 3.8 and 3.9). In Figure 3.9, note the extent to which a bridge is screened by trees. The approaches to the new river bridge are similar in height to the bridge in this image. Figure 3.10 is a location map of the computer visualization of TH 95 shown in Figure 3.11. Outward views for motorists will be primarily of forest plants indigenous to the St. Croix river terraces. A list of trees and shrubs for the interchange area is provided in Table 3.1.

Native trees and shrubs should be planted, outside of the clear zones, between the various roadways, and also beneath the main bridge approach structure and the el-evated ramp structures east of TH 95. Several species of deciduous trees and shrubs are suitable for the partial shade that will be cast by the high overhead roadway structures. Moving from west to east, vertical clearanc-es under the elevated roadways will increase to the ex-tent that tall growing trees can be planted beneath the bridge approaches. The elevated structures may slightly limit the amount of rainfall reaching the ground for plants; however, this reduction in precipitation will be slight due to windblown rain, surface runoff, and suf-ficient groundwater. Under the west (abutment) ends of the elevated structures, where vertical clearances are reduced, it will be appropriate to use mostly shade tolerant and drought resistant plants to vegetate these

table 3.1Suggested Tree and Shrub List

Common Name Botanical Name

Lower Bench—East of TH 95

Trees

Green Ash Fraxinus pennsylvanica Basswood Tilia americana Black Ash Fraxinus nigra Red Oak Quercus rubra Red Maple Acer rubrum Silver Maple Acer saccharinum Cottonwood Populus deltoides

Shrubs

American Hazelnut Corylus americanaGray Dogwood Cornus racemosaPagoda Dogwood Cornus alternifoliaSpeckled Alder Alnus incanaWinterberry Ilex verticillata

Upper Bench—West of TH 95

Trees

Red Oak Quercus rubra Basswood Tilia americana White Oak Quercus alba Red Maple Acer rubrum Sugar Maple Acer saccharum Paper Birch Betula papyrifera Green Ash Fraxinus pennsylvanica

Shrubs

Prickly Gooseberry Ribes cynosbatiPagoda Dogwood Cornus alternifoliaNannyberry Viburnum Viburnum lentagoRed Elderberry Sambucus pubens



chapter 3Minnesota TH 36/TH 95 Interchange

figure 3.5Plan View of “River Terrace Forest” Landscape Concept for the TH 36/TH 95 Interchange

3-5

400

NORT

H100 0 200

scale in feet

TH 36

Bri

dge

TH 95

TH 36

Stormwater pond with naturalized edges

To Stillwater

Loop Trail

Entrance Ramp

Exit Ramp

Exit Ramp

Entrance Ramp

Existing Wetland

Stormwater storage/treatment pond as “Natural Wetland” or marsh

Beac

h R

oad

TH 36 Bridge over TH 95

Deciduous trees & shrubsnative to St. Croix River Terraces

Upland oak savannain vicinity of Beach Road

St. Croix River

To Bayport

VQM




figure 3.5Plan View of “River Terrace Forest” Landscape Concept for the TH 36/TH 95 Interchange

3-5




figure 3.6Cross-Section Illustration of Landscape Concept for TH 36 in the TH 36/TH 95 Interchange


3-7

100 0 100

scale in feet

Westbound Entrance Ramp from TH 95

Deciduous Trees & Shrubs Native to St. Croix River Valley

TH 36 Eastbound & Westbound Lanes

Eastbound Exit Ramp to TH 95

Stormwater Pond with Naturalized Edges

Deciduous Trees & Shrubs Native to St. Croix River Terraces

Southbound Thru & Turn Lanes

Northbound Thru & Turn Lanes

Loop Trail

Stormwater Pond with Naturalized Edges

VQM






3-7



3-9

figure 3.9Highway Bridge Structure in Wooded or Forested Landscape

figure 3.8Highway with Wooded Roadside – Note clear zones along roadway


areas. Near the abutments, a lack of precipitation to support plant growth may require ground areas to be stabilized with crushed rock, concrete, or rip rap.

In developing planting plans for the interchange, highway safety and maintenance concerns must be addressed. Plants will need to be positioned so they do not obstruct sight lines or impinge on clear zone setbacks and snow storage areas. While adhering to highway operational and safety requirements, the lay-out of plants near and along roadsides should be done in a way that creates an irregular or meandering edge, not a uniform edge that parallels the roadway. Also, along the roadsides, shrubs and lower story small trees should create a visual transition to larger, taller vegeta-tion. Shrubs can potentially be planted in clear zones to create this irregular edge and vertical transition. It will be necessary to provide a mow strip between shrubs and roadway shoulder (Figure 3.12).

Stormwater treatment ponds in and near the inter-change should have the appearance of natural ponds, similar in character to the kettle ponds that occur nearby. Further discussion on the visual character of stormwater ponds and other drainage features is pro-vided in Chapter 9, Design Elements.

The new river bridge will include an anti-icing system. A building housing anti-icing equipment and materi-als for the river bridge will be located on the treatment plant access road under the river bridge. This location is well screened from the river and the roadways due to the lower elevation and mature vegetation.

South of the interchange, toward Bayport, a retaining wall is required to support a trail west of the Pickett stormwater ponds. The length and location of the wall creates a strong visual image, see Figure 3.13. Chapter 7, Loop Trail and Other Trails, Section 7.5.1, Minnesota TH 95 South, provides additional description of the treatment of the trail and wall.



3-10

figure 3.10Location Map of Visualizations


TH 95 will serve as an entrance or “gateway” to the cities of Stillwater, Oak Park Heights, and Bayport. Chapter 9, Design Elements, Section 9.9, Community Gateway Areas, discusses the purpose and examples of community gateways with recommendations for local

gateway themes and elements. Further local involve-ment will be required to develop community gateway themes if the treatment is desired on these roadway segments.




figure 3.11TH 95 Visualization

3-11

VQM




figure 3.11TH 95 Visualization

3-11



3-13

figure 3.12Cross-Section Illustration of Typical Plant-ing Conditions along Highways and Ramps

RoadwayLow to medium shrubs

Large shrubs and small trees

Large trees





figure 3.13Bayport Retaining Wall Visualization

3-15

VQM




figure 3.13Bayport Retaining Wall Visualization

3-15

chapter 3 minnesota th 36/th 95 interchange 3.pdfinterchange (figure 3.2). as a result of the...

Documents