WILDLIFE CROSSING DESIGN RECOMMENDATIONS: INNOVATION IN OVERPASS DESIGN July 2014
ARC
TRANSPORTATION PLANNING & WILDLIFE MITIGATION INTEGRATED DESIGN APPROACH
(3)
(4)
SITE & CONTEXT ECOLOGY STRUCTURE
INNOVATION: MATERIALS + DESIGN (9) WEATHERED - STRUCTURAL STEEL GRID : THE OLIN STUDIO (11) (13) PRE-CAST CONCRETE : HNTB & MVVA (17) THIN-SHELL CONCRETE : ZJA ZWARTS & JANSMA ARCHITECTS WOOD-CORE FIBERGLASS : JANET ROSENBERG & ASSOCIATES GLUE LAMINATED TIMBER : BALMORI ASSOCIATES (23)
COSTING (25) SITE ANALYSIS VALUE ADDED
REFERENCES & RESOURCES CREDITS
(30)
(29)
(21)
WHY IS IT IMPORTANT TO ENSURE SAFE PASSAGE FOR HUMANS AND ANIMALS?
Wildlife-vehicle collisions pose a significant danger to human safety and to wildlife populations. In North America, the number of collisions between wildlife and vehicles has increased 50% in the past 15 years.1 Growing numbers of wildlife-vehicle collisions with large animals lead to personal injury, property damage, and rising insurance premiums. Road networks fragment natural landscapes into disconnected patches in which wildlife must live and move to access food, shelter, and mates. Wildlife road mortality is a major threat to the survival of 21 federally listed threatened or endangered species in North America.2 WILDLIFE CROSSING INFRASTRUCTURE IS A PROVEN SOLUTION
TRANSPORTATION PLANNING & WILDLIFE MITIGATION 3
Roads must be redesigned for the safe passage of two clients: driver and animal. Re-purposing existing bridge designs is insufficient to achieve successful mitigation because wildlife crossings serve a unique function -simultaneously facilitating the movement of vehicles along roads and bridging habitats for animal mobility. An integrated design approach is essential to merge structural engineering and ecological design. INTEGRATED DESIGN APPROACH
Image Credit: HNTB & MVVA 4
+ SITE & CONTEXT
+ ECOLOGY
5
STRUCTURE
SITE ANALYSIS Site analysis and information gathering are necessary to assess the suitability of a potential crossing location and to determine the most appropriate crossing structure design given local conditions. Factors to consider when choose a site and determining a suitable intervention are outlined in Site Analysis (p. 24).
SITE SELECTION CRITERIA Road mortality and wildlife-vehicle collision data are the primary sources of data used to identify an appropriate site for the installation of a wildlife crossing. Research into animal behavior has identified additional factors to consider in the placement of a crossing structure and the positioning of access points. Animals travel along paths of least resistance between destinations. Environmental characteristics that are likely to attract wildlife to move along a pathway include: • interruption in contiguous canopy cover • sloped topography that descends towards roadway • gently sloped ramps leading onto overpass • presence of surface water
6
SITE & CONTEXT
Successful wildlife crossing structures carry the landscape over the roadway and integrate seamlessly with the surrounding environment. To achieve an integrated design, a detailed understanding of the local ecology is necessary.
ECOLOGICAL DESIGN Appropriate selection of vegetation and substrate in response to environmental conditions and target species represents a large proportion of design consideration and cost necessary for the construction of a crossing structure. The design of the superstructure must: • behave as an extension of habitats present on either side of the crossing • distill multiple habitat types into corridors along the structure • provide both open and covered movement opportunities depending on species’ preferences
EXCLUSIONARY FENCING Exclusionary fencing is necessary to direct wildlife to crossing structures and prevent entry onto roadways in unsafe locations. Fencing on both sides of the crossing structure, at a height of 2.4m, should extend 500m along the road shoulder in each direction.
Sample cross section of multiple habitat types targeted towards species local to Western Alpine region planted across width of crossing structure. Image Credit: HNTB & MVVA
7
ECOLOGY
planting fill habitat design
ramp abutments beam deck pillars (or pillar-less)
SUPERSTRUCTURE
SUBSTRUCTURE
The design of the crossing substructure and the constructed ecology of the superstructure must be considered in tandem. While the design solutions presented in this brief vary, certain features are common to most structures (See: above). The width of the crossing structure is integral to its success as a mitigation tool. Recommendations for overpasses targeted at large animals cite a minimum width of 130–165 ft (4050m), and recommend 165–230 ft (50-70m) for optimal performance.3 Factors influencing the necessary width of a wildlife crossing include: preferences of target species, number of target species, and number of habitat types which must be accommodated along the crossing structure (See: Ecology, p. 7).
E
TUR C U R T ING S
H WIDT
SS O R C OF
STRUCTURE
Image Credit: HNTB & MVVA 8
The 2010 ARC International Wildlife Crossing Infrastructure Design Competition challenged teams to develop crossing infrastructure that is efficient, ecologically responsive, safe, and flexible. These designs can be readily adapted for widespread use in various locations and offer flexibility for wildlife mobility under dynamic ecosystem conditions, including climate change. An integrated design approach was achieved through cross-disciplinary collaboration between specialists in the fields of engineering, landscape architecture, and ecological science. The material and design innovations generated by five finalist teams in the ARC Competition are featured in this brief. Additional design concepts are available through ARC Solutions.
For more information about the ARC International Wildlife Crossing Design Competition please see the Competition Video.
INNOVATION: MATERIALS + DESIGN 9
OPTION 1 material: Weathered Structural Steel Grid designed by: The Olin Studio
OPTION 2 material: Pre-Cast Concrete designed by: HNTB & MVVA
OPTION 3 material: Thin-Shell Concrete designed by: ZJA Zwarts & Jansma Architects
OPTION 4 material: Wood-Core Fiberglass designed by: Janet Rosenberg & Associates
OPTION 5 material: Glue-Laminated Timber designed by: Balmori Associates
10
MATERIAL DESCRIPTION This design has three major elements: a modular diagrid structure, reinforced by rhomboid-shaped habitat inserts, supported by nine discreet piers. Bridge structure design and planting approach are exclusively connected -- the landscape is arranged using contained vegetative modules slotted into the grid structure. As a preventative measure against varied weather conditions, bolted weathered-structural steel is proposed for the modular diagrid structure. The piers are constructed from prefabricated ultra-high resistance concrete (Ductal®) which outperforms cement and concrete in compressive strength, flexural resistance, and durability. To maintain the lightweight quality of the overall crossing, each habitat module insert is fabricated using glass reinforced plastic (GRP), a composite plastic reinforced by fine glass fibers.
BRIDGE DESIGN SPECIFICATIONS & ASSETS curved (‘winged’) toroid surface serves multiple purposes: • delivers a standardized approach for easy duplication of design • provides shade to interior forest when the sun is at lower angles • offers greater amount of sunlight to the underside of the crossing • shields animals from oncoming traffic noise
innovative form -- diagrid structure: • allows for even and consistent distribution of load and stress using minimal structural material modular, replicable and cost-effective system: • bridges can be added and removed to complement physical modifications of highways • habitat modules can be reused and adapted to meet present and future ecological conditions
minimal site disturbance during installation: • design requires minimal on-site assembly • habitat modules can be pre-planted at nurseries and craned into place
WEATHERED STRUCTURAL STEEL GRID : THE OLIN STUDIO 11
From top to bottom: landscape modules, stick frame analysis, fencing and diagrid structural frame, drainage visualized, support structure.
Layers of a singular habitat module.
Image Credit: The Olin Studio 12
MATERIAL DESCRIPTION Concrete is a widely used, readily available, familiar, and cost-effective material. This design capitalizes on these assets by using concrete in an innovative way -- using a singular structural element adapted from widely used pre-cast formwork to achieve a streamlined bridge design.
BRIDGE DESIGN SPECIFICATIONS & ASSETS modular and cost-effective system: • bridges can be added and removed as migration patterns shift over time
uses only straight line formwork: • commercially available forms are readily adaptable for use as hypar formwork
minimal site disturbance during installation: • only light trenching required • designed to be lifted and erected using single rubber tired mobile hydraulic crane
fully pre-cast hypar vault streamlines construction: • serves as combination of abutment, beam, deck and eliminates need for central pier • no on-site concrete work required
components lock together forming scuppers that shed water: • does not require conventional waterproofing
hypar module can be deployed as a structural component of additional crossing structure features: • bike tunnel, sound barrier, retaining wall, and scaffold for exclusionary fencing
pillar-free design • advantageous in winter climates
13
PRE-CAST CONCRETE : HNTB & MVVA
Cross section of sub- and superstructure design.
Image Credit: HNTB & MVVA 14
Left to Right: Hypar-vault module serves as combination of abutment, beam, and deck; individual hyper-vault module pictured.
Hypar-vault element can be used in multiple ways as a structural component of accessory features (bike tunnel, sound barrier, retaining wall, exclusionary fencing).
Image Credit: HNTB & MVVA
15
PAGE LEFT BLANK
16
MATERIAL DESCRIPTION This design presents a unique combination of structures: membrane (for formwork) and shell (for permanent structure). Replacing traditional formwork with a flexible and durable geofabric membrane allows for the production of ultra thin concrete shells that are cost-effective, structurally sound, and aesthetically pleasing. The shell is composed of UHSC (ultra high strength concrete) with steel fiber reinforcements. This combination of materials offers natural resistance against crack formations resulting from shrinkage.
BRIDGE DESIGN SPECIFICATIONS & ASSETS minimal road traffic and site disturbance during installation
prefabricated thin-shell concrete minimizes materials, costs and timelines: • temporary support structures designed to be reused for up to 10 wildlife crossings of similar concept
innovative and creative use of ‘dissolvable’ fencing: • passively conditions animal behavior, throughout the lifespan of the fence • mitigates predation effects that may arise from ecopassage installation
double-curved surface serves multiple purposes: • minimizes stress surfaces • provides shade to interior forest • offers maximum sunlight to the underside of the structure • protects against noise and lights from the highway
design includes system of ponds • attracts and accommodates wider range of species pillar-free design • advantageous in winter climates
THIN-SHELL CONCRETE : ZJA ZWARTS & JANSMA ARCHITECTS 17
This team created a video illustrating their design concept.
Elements of substructure: steel cable grid provides form for concrete shell..
Layers of proposed overpass design.
Image Credit: ZJA Zwarts & Jansma Architects 18
Cross section of design concept at road median.
landscape 1, span 60m 4 lane road clearance 5.5m adaptable structure example 1
landscape 2, span 40m 4 lane road clearance 7m adaptable structure example 2
landscape 3, span 100m 6 lane road clearance 5.5m adaptable structure example 3
Multiple configurations of crossing design can be adapted to varying road spans and site conditions. Image Credit: ZJA Zwarts & Jansma Architects
19
PAGE LEFT BLANK
20
MATERIAL DESCRIPTION Wood-core fiberglass composite material is both lightweight and strong; fiberglass coating prevents wood-core from rotting. Crossing structure is constructed using repetition of single form that is rotated to produce either a line or a curve. Modules can be arranged to create multiple corridors and to allow for modification of width and position in response to site constraints.
BRIDGE DESIGN SPECIFICATIONS & ASSETS simple construction -- one material only: • deck composed of only two planar sections, supported by beams that are supported by columns
can be prefabricated to reduce costs and timelines: • simplifies construction process and minimizes disruption material absorbs impact noise
avoids carbon emissions associated with other building materials fiberglass coating: • can be tinted to any color, to blend with landscape or stand out visually • naturally resistant to graffiti
lighter and more durable than other building materials: (e.g. concrete): • service life of 100+ years
WOOD-CORE FIBERGLASS : JANET ROSENBERG & ASSOCIATES 21
Aerial view of proposed crossing structure.
Cross section of wood-core fiberglass material. Various configurations possible using strand system.
Image Credit: Janet Rosenberg & Associates 22
MATERIAL DESCRIPTION Increasing temperatures in western North America have enabled mass outbreaks of pine beetles that have decimated vast quantities of pine trees. Recognizing the positive environmental, economic, and social implications of capitalizing on locally available beetle-killed blue pine, Balmori proposes a monolithic bridge structure made entirely of glue-laminated timber. This design can be modified to take advantage of other locally available timber species.
BRIDGE DESIGN SPECIFICATIONS & ASSETS structure’s core designed as a wide continuous beam, devoid of joints: • beams react with its section height to absorb and minimize stress surfaces • reduces material required and maintenance costs
adopts a cradle to cradle, regenerative approach: • harvests readily and locally available material for construction pillar-free design: • advantageous in winter climates glue-laminated timber technology: • superior durability protects against impacts of humidity, fire, and chemicals. • reduces carbon footprint
embraces simple and flexible low-tech system of layering timber planes: • bridge shape can be easily modified by repositioning timber planes to meet present and future ecological conditions • avoids closing highway during construction
GLUE-LAMINATED TIMBER : BALMORI ASSOCIATES 23
Cross section of overpass design.
Wood planes are layered to construct overpass
Image Credit: Balmori Associates 24
The cost to implement a wildlife crossing structure is estimated based on four key elements: 1. professional design and consultation fees (engineering, ecology, landscape architecture); 2. site planning (land-tenure, leasing, approvals); 3. essential site-work (grading, tree removal, trenching, remediation); and, 4. construction (materials, roadway alteration, sub- and superstructure, approach ramps, surface and adjacent habitat creation, exclusionary fencing, berms to mitigate noise and light penetration). Ecological design strategies and planting materials will differ based on site specific variables such as climate and target species as well as the design specifications associated with the crossing substructure. To achieve an integrated design these costs must be considered in tandem.
COSTING 25
SITE • • • • • • •
topography slope aspect geomorphology presence of existing structure potential for adaptive reuse substrate type, composition geophysical conditions soil composition, texture, drainage
ROAD
• • • • • • •
span/# of lanes present & planned traffic volume collision statistics surface material speed limit visibility construction constraints road closing, temporary traffic control
CLIMATE
ECOLOGY
POLICY
• • • • • •
• target species and associated habitat requirements • diversity, abundance, and rarity • migration patterns • local and regional vegetation • canopy cover • soil quality and depth • surface water availability quality, quantity, location
• land tenure • easement • ownership present & future
local weather patterns elevation snow load precipitation humidity freeze/thaw cycles
A detailed site analysis is a necessary initial step in the process of implementing a wildlife crossing. Clearly defined site conditions are necessary for ecological design and engineering consultants to accurately estimate costs and to tailor crossing designs to site constraints and opportunities for effective mitigation.
COST SAVINGS & EFFICIENCIES Designs generated in the ARC Design Competition achieve cost savings through material selection, potential for off-site assembly, minimized site disturbance during installation, modularity, and reduced need for maintenance. To review the assets and efficiencies associated with individual design solutions refer to Innovation + Materials (p. 9-22). An independent review has confirmed that the implementation of a finalist entry in the ARC Competition is less costly than comparable existing crossing structures in Banff National Park. Additional ways in which cost savings can be achieved during the planning and implementation process include: • planned road resurfacing projects that overlap with identified ecological hotspots can be used as opportunities to install wildlife crossings • fill can be sourced from local construction projects and reused in crossing construction • planning for the installation of a network of crossings provides long-term cost savings as the initial investment (e.g. in formwork) significantly reduces the cost of implementing additional crossing structures
SITE ANALYSIS 26
Wildlife crossings provide opportunities for both physical and virtual observation, education, and engagement.
OBSERVATION & EDUCATION Opportunities for unobtrusive observation and learning can be incorporated in proximity to crossing structures to engage public curiosity and to initiate a dialogue about the efforts of state agencies to make highways permeable for wildlife and to minimize wildlife-vehicle collisions. Wildlife crossings serve an educational function by weaving together narratives of shared landscapes, ecosystem protection, and scientific literacy. Benefits to tourism and economic development can be derived from visitors to crossing structures by way of increased traffic to other local landmarks and attractions.
VALUE ADDED
Image Credit: (top) The Olin Studio; (bottom) HNTB & MVVA
27
MONITORING Crossing structures function as living laboratories offering the potential to foster long-term research and learning opportunities by way of ongoing monitoring and research programs. Assessing the function of wildlife crossings, based on well-designed monitoring efforts, can provide reliable data to inform adaptive management of future wildlife mitigation designs and pave the way for innovation in materials and design.
Image Credit: CNE/Rocky Mountain Wild; (lynx) Parks Canada 28
arc-solutions.org competition.arc-solutions.org
1
Huijser, M.P., J.W. Duffield, A.P. Clevenger, R.J. Ament, and P.T. McGowen, 2011. Cost–Benefit Analyses of Mitigation Measures Aimed at Reducing Collisions with Large Ungulates in the United States and Canada: a Decision Support Tool. Ecology and Society, 14(2): 15. http://www.ecologyandsociety.org/viewissue.php?sf=41
Van der Ree, R., Jaeger, J. A. G., van der Grift, E., Clevenger, A. P. (guest editors). 2011. Effects of Roads and Traffic on Wildlife Populations and Landscape Function. Ecology and Society, 16(1): 48. http://www.ecologyandsociety.org/viewissue.php?sf=41
2
3
Federal Highway Administration (2011). Wildlife Crossing Structure Handbook: Design and Evaluation in North America. Publication No. FHWA-CFL/TD-11-003, pp. 1-223.
29
RESOURCES & REFERENCES
PROFESSIONAL ADVISOR
BRIEF DESIGN & EDITING
Professor Nina-Marie Lister MCIP, RPP, Affiliate ASLA Cell 416.704.5736 | Office 416.979.5000 x6769 nm.lister@ryerson.ca
Marta Brocki & Jessica Yuan mbrocki@ryerson.ca | jessyuan@ryerson.ca
FINALIST TEAM CREDITS Balmori Associates (New York, NY)
Janet Rosenberg & Associates (Toronto, ON)
Studio MDA
Dougan & Associates
Knippers Helbig David Skelly
HNTB with Michael Van ZJA Zwarts & Jansma Valkenburgh & Associates Architects (New York, NY) (Amsterdam, NL) Applied Ecological Services
The Olin Studio (Philadelphia, PA)
OKRA Landscape Architects
Buro Happold
EkoCare International
IV-Infra
Explorations Architecture
Blackwell Bowick Partnership
Planecologie
Applied Ecological Services
Bluegreen
Arcadis
John A. Martin & Associates
Bates Engineering
Davis Langdon
ETH Zurich
CITA
Witteveen + Bos
30
CREDITS