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WILDLIFE CROSSING STRUCTURE HANDBOOK Design and Evaluation in North America

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Publication No. FHWA-CFL/TD-11-003
March 2011

Central Federal Lands Highway Division
12300 W. Dakota Ave.
Lakewood, CO 80228

Front Materials

• Cover
• Foreword
  • Notice
  • Quality Assurance Statement
• Technical Report Documentation Page
• Units of Measurement
• Table of Contents
  • List of Figures
  • List of Tables

Cover

Foreword

The Federal Highway Administration (FHWA) encourages programs that protect both wildlife and roadway users when the two groups eventually interact. An ever increasing human population demands safe and efficient access to their facilities, but this often comes with the need to mitigate the compromises to the animal habitats. Safety of drivers and preservation of animals are important components that when they successfully mesh we achieve major program goals for improved safety, enhanced livability, and protection of the environment.

This FHWA report called the Wildlife Crossing Structure Handbook offers key background information on defining the overall wildlife-vehicle interaction problem, the needs to be addressed, and offers a multitude of tangible solutions to plan, design, construct, monitor and maintain effective critter crossings. This handbook is for all transportation, environmental, wildlife resource, and stakeholder officials who strive to preserve and reweave safe corridor passages for animals and vehicle travelers.

F. David Zanetell, P.E., Director of Project Delivery
Federal Highway Administration
Central Federal Lands Highway Division

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The FHWA provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

Technical Report Documentation Page

1. Report No. FHWA-CFL/TD-11-003	2. Government Accession No.			3. Recipient's Catalog No.
4. Title and Subtitle Wildlife Crossing Structure Handbook Design and Evaluation in North America				5. Report Date March 2011
				6. Performing Organization Code
7. Author(s) Anthony P. Clevenger and Marcel P. Huijser				8. Performing Organization Report No.
9. Performing Organization Name and Address Western Transportation Institute P.O. Box 174250 Bozeman, MT 59717-4250				10. Work Unit No. (TRAIS)
				11. Contract or Grant No. DTFH61-03-P-00398
12. Sponsoring Agency Name and Address Federal Highway Administration Planning, Environment and Reality 1200 New Jersey Ave., SE Washington, DC 20590				13. Type of Report and Period Covered Final Report, August 2003 - February 2011
				14. Sponsoring Agency Code HEPM-30
15. Supplementary Notes COTR: Paul Garrett, FHWA-HQ. Advisory Panel Members: Mary Gray and Corrie Veenstra, FHWA- HQ; Brian Allen, FHWA-FLH; and Roger Surdahl, FHWA-CFLHD. This project was funded under the FHWA's Surface Transportation Environment and Planning Cooperative Research Program (STEP).
16. Abstract This handbook provides numerous solutions to wildlife-vehicle interactions by offering effective and safe wildlife crossing examples. It initially describes the critter crossing problem and justifies the need to solve it. Project and program level considerations are identified for planning, placement and design of wildlife crossing structures. Key design and ecological criteria, construction and maintenance guidelines, and effective monitoring techniques are shown and described in this handbook's practical application examples called Hot Sheets.
17. Key Words ANIMAL MOVEMENT BARRIERS, HABITAT CONNECTIVITY, HABITAT LOSS, ROAD ECOLOGY, WILDLIFE CROSSING, WILDLIFE MORTALITY, WILDLIFE-VEHICLE INTERACTION			18. Distribution Statement No restriction. This document is available to the public from the sponsoring agency at the website http://www.cflhd.gov.
19. Security Classif. (of this report) Unclassified		20. Security Classif. (of this page) Unclassified			21. No. of Pages 224	22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

SI* (MODERN METRIC) CONVERSION FACTORS

APPROXIMATE CONVERSIONS TO SI UNITS
Symbol	When You Know Multiply By To Find	Symbol
	LENGTH
in	inches 25.4 Millimeters	mm
ft	feet 0.305 Meters	m
yd	yards 0.914 Meters	m
mi	miles 1.61 Kilometers	Km
	AREA
in2	square inches 645.2 Square millimeters	mm2
ft2	square feet 0.093 Square meters	m2
yd2	square yard 0.836 Square meters	m2
ac	acres 0.405 Hectares	ha
mi2	square miles 2.59 Square kilometers	km2
	VOLUME
fl oz	fluid ounces 29.57 Milliliters	mL
gal	gallons 3.785 Liters	L
ft3	cubic feet 0.028 cubic meters	m3
yd3	cubic yards 0.765 cubic meters	m3
NOTE: volumes greater than 1000 L shall be shown in m3
	MASS
oz	ounces 28.35 Grams	g
lb	pounds 0.454 Kilograms	kg
T	short tons (2000 lb) 0.907 megagrams (or "metric ton")	Mg (or "t")
	TEMPERATURE (exact degrees)
°F	Fahrenheit 5 (F-32)/9 Celsius or (F-32)/1.8	°C
	ILLUMINATION
fc	foot-candles 10.76 Lux	lx
fl	foot-Lamberts 3.426 candela/m2	cd/m2
	FORCE and PRESSURE or STRESS
lbf	poundforce 4.45 Newtons	N
lbf/in2	poundforce per square inch 6.89 Kilopascals	kPa
APPROXIMATE CONVERSIONS FROM SI UNITS
Symbol	When You Know Multiply By To Find	Symbol
	LENGTH
mm	millimeters 0.039 Inches	in
m	meters 3.28 Feet	ft
m	meters 1.09 Yards	yd
km	kilometers 0.621 Miles	mi
	AREA
mm2	square millimeters 0.0016 square inches	in2
m2	square meters 10.764 square feet	ft2
m2	square meters 1.195 square yards	yd2
ha	Hectares 2.47 Acres	ac
km2	square kilometers 0.386 square miles	mi2
	VOLUME
mL	Milliliters 0.034 fluid ounces	fl oz
L	liters 0.264 Gallons	gal
m3	cubic meters 35.314 cubic feet	ft3
m3	cubic meters 1.307 cubic yards	yd3
	MASS
g	grams 0.035 Ounces	oz
kg	kilograms 2.202 Pounds	lb
Mg (or "t")	megagrams (or "metric ton") 1.103 short tons (2000 lb)	T
	TEMPERATURE (exact degrees)
°C	Celsius 1.8C+32 Fahrenheit	°F
	ILLUMINATION
lx	lux 0.0929 foot-candles	fc
cd/m2	candela/m2 0.2919 foot-Lamberts	fl
	FORCE and PRESSURE or STRESS
N	newtons 0.225 Poundforce	lbf
kPa	kilopascals 0.145 poundforce per square inch	lbf/in2

*SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380 (Revised March 2003)

Table of Contents

• CHAPTER 1 - INTRODUCTION
  • BACKGROUND
  • JUSTIFICATION
  • OBJECTIVES
  • ORGANIZATION
  • SUGGESTED READING
• CHAPTER 2 - WILDLIFE POPULATIONS AND ROAD CORRIDOR INTERSECTIONS
  • INTRODUCTION
  • THE ECOLOGY OF ROAD CORRIDORS
  • IMPACTS OF ROADS ON WILDLIFE POPULATIONS
    • Change In Habitat
    • Change In Wildlife Distribution
  • ROAD-RELATED MORTALITY VS. BARRIER EFFECTS
  • SUGGESTED READING
• CHAPTER 3 - IMPACT IDENTIFICATION, REMEDIATION, PLANNING AND PLACEMENT
  • INTRODUCTION
  • STARTING OUT
    • Rule of Thumb: Avoid, Mitigate or Compensate
  • SCALED HABITAT CONNECTIVITY PLANNING
    • Project-Level Approaches
    • Systems-Level or Landscape-Level Approaches
  • PLANNING RESOURCES
    • Maps and Data
    • GIS Layers
    • How To Site Wildlife Crossings
  • FIELD DATA
    • Physical Data
    • GIS-Based Movement Model
    • No Data
  • SUGGESTED READING
• CHAPTER 4 - DESIGNS, TOOLBOXES, GUIDELINES, AND PRACTICAL APPLICATIONS
  • INTRODUCTION
  • FUNCTION OF WILDLIFE CROSSINGS AND ASSOCIATED MEASURES
  • SPACING OF WILDLIFE CROSSINGS
  • GUIDELINES FOR THE SELECTION OF WILDLIFE CROSSINGS
    • Wildlife Crossing Design Types (Appendix C, Hot Sheets 1-11)
    • Wildlife Habitat Connectivity Potential
    • Topography
  • WILDLIFE SPECIES GROUPS AND CROSSING STRUCTURE CLASSIFICATION
  • DESIGN AND DIMENSIONS
    • General Design Specifications For Wildlife Species
    • Specific Design of Wildlife Crossings and Adjacent Habitat
    • Hot Sheets 1-11 - Wildlife Crossing Prescriptions (Appendix C)
    • Hot Sheets 12-14 - Fencing and Gate Guidelines (Appendix C)
  • SUGGESTED READING
• CHAPTER 5 - MONITORING TECHNIQUES, DATA INTERPRETATION, AND EVALUATIONS
  • CONSERVATION VALUE OF WILDLIFE CROSSINGS
  • AN APPROACH FOR MONITORING IMPACTS
  • MONITORING AND ASSESSMENT GUIDELINES
  • SETTING MONITORING AND PERFORMANCE TARGETS
    • Developing Performance Targets - Who Defines Them?
    • Reliably Detecting Change in Target Parameters
    • Developing Consensus-Based Performance Targets
  • FOCAL SPECIES
  • MONITORING TECHNIQUES
  • STUDY DESIGNS TO MEASURE PERFORMANCE
    • Inferential Strength
    • Types of Study Design and Resulting Inferential Strength
  • ADAPTIVE MANAGEMENT
  • SUGGESTED READING
• APPENDIX A - GLOSSARY
• APPENDIX B - COMMON AND SCIENTIFIC NAMES
• APPENDIX C - HOT SHEETS
  • HOT SHEET 1: LANDSCAPE BRIDGE
  • HOT SHEET 2: WILDLIFE OVERPASS
  • HOT SHEET 3: MULTI-USE OVERPASS
  • HOT SHEET 4: CANOPY CROSSING
  • HOT SHEET 5: VIADUCT OR FLYOVER
  • HOT SHEET 6: LARGE MAMMAL UNDERPASS
  • HOT SHEET 7: MULTI-USE UNDERPASS
  • HOT SHEET 8: UNDERPASS WITH WATERFLOW
  • HOT SHEET 9: SMALL-TO-MEDIUM-SIZED MAMMAL UNDERPASS
  • HOT SHEET 10: MODIFIED CULVERT
  • HOT SHEET 11: AMPHIBIAN/REPTILE TUNNEL
  • HOT SHEET 12: FENCING - LARGE MAMMALS
  • HOT SHEET 13: FENCING - SMALL AND MEDIUM VERTEBRATES
  • HOT SHEET 14: GATES AND RAMPS
• APPENDIX D - FRAMEWORK FOR MONITORING
• APPENDIX E - MONITORING TECHNIQUES
• APPENDIX F - OTHER HANDBOOKS AND GUIDELINES
• APPENDIX G - PROFESSIONAL AND TECHNICAL JOURNALS

LIST OF FIGURES

• Figure 1. Photo. Accidents with wildlife in rural and suburban areas are becoming a major safety concern for motorist and transportation agencies (credit: John Nordgren)
• Figure 2. Photo. Wildlife crossings are becoming more common in highway expansion projects in North America. An example is the Greenway Landbridge on Interstate 75 in Marion County, Florida (Credit: Google Earth)
• Figure 3. Photo. The highway system in the United States is used by more than 200 million vehicles and covers more than 6.2 million km (Credit: Tony Clevenger)
• Figure 4. Schematic. Increasing road density fragments habitat into smaller patches and creates a disproportionate amount of edge habitat (from Iuell 2005)
• Figure 5. Schematic. Barrier effects on populations. (A) A metapopulation consists of a network of local subpopulations that may vary in size and local dynamics but are linked to each other through dispersal. (B) Road construction causes a disturbance and loss of local populations within the network. In addition, infrastructure imposes a barrier to dispersal that can prevent recolonisation and isolate local subpopulations from the rest of the metapopulation. If important source populations are cut off from the remaining sink populations, the entire metapopulation may be at risk of extinction (from Iuell 2005)
• Figure 6. Graph. Results of studies on the impact of traffic noise on breeding bird populations in The Netherlands. When the noise load exceeds a threshold of between 40 and 50 dBA, bird densities were found to drop significantly. The sensitivity to noise and the threshold is different between species and between forested and open habitats (from Reijnen, Veenbaas and Foppen 1995)
• Figure 7. Photo. Mountain goats attracted to roadside vegetation along Highway 93 South in Kootenay National Park, British Columbia, Canada (Credit: Tony Clevenger)
• Figure 8. Photo. Right-of-ways can vary considerably between different landscapes and parts of North America. Left: A two-lane highway in Jasper National Park. Dense vegetation of plants, shrubs and trees along roads provide potential nesting sites for birds and screen the road and its traffic from the surrounding landscape. Right: Interstate-65 in Kentucky consisting of a wide right-of-way with little native vegetation. (Credits: Tony Clevenger)
• Figure 9. Graph. Conceptual model on the effect of traffic volume on the percentage of animals that successfully cross a road, are repelled by traffic noise and vehicle movement, or get killed as they attempt to cross. The conceptual model indicates that most collisions occur on intermediate roads (from Seiler 2003)
• Figure 10. Photo. Lynx photographed using a wildlife overpass, as part of crossing structure monitoring along the Trans-Canada Highway in Banff National Park, Alberta. Long-term monitoring of the wildlife crossings in Banff has enabled the documentation of the crossings used by locally rare carnivores such as Lynx, and Wolverine (Credit: Tony Clevenger/WTI/Parks Canada)
• Figure 11. Schematic. Representation of road construction and habitat (A) fragmentation (B) avoidance (C) mitigation by use of under/overpasses, and (D) compensation by creation of replacement habitat nearby (from Iuell et al. 2005)
• Figure 12. Schematic. Location of alignment of highways with respect to habitat quality may have differential impacts on wildlife movements (dotted line). The impact of a highway alignment located on the periphery in sub-optimal habitat (yellow) would be expected to impact wildlife movements less than if the disturbance equally bisected optimal habitat (green)
• Figure 13. Map. A project-scale analysis of connectivity emphasis areas (CEA) for the Interstate 90 Snoqualmie Pass East project area, Washington State. These are locations where wildlife crossing mitigations are proposed to be installed
• Figure 14. Map. Statewide mapping of highways and fracture zones, blocks of wildlife habitat and connectivity linkage zones for Arizona (Source: Arizona Wildlife Linkages Work Group)
• Figure 15. Map. Global position system (GPS) movement data from a male brown bear crossing a major four-lane highway and wildlife crossings (blue circle) in Croatia (Source: D. Huber, Zagreb University)
• Figure 16. Photo. (A) Use of track beds is one method for obtaining information on wildlife movement across roads and key crossing locations prior to installation of wildlife crossing structures. (B) Raking of track beds along US 93 in Montana to collect pre-mitigation information on wildlife movements in the highway corridor (Credits: M. Huijser)
• Figure 17. Map. DNA sampling grid in Banff National Park. Hair snag sites and rub tree sites were used to collect population genetic data on individuals in the population and from bears using the wildlife crossings on the Trans-Canada Highway (Source: WTI/Parks Canada). 35
• Figure 18. Chart. Types of measures used to reduce the impacts of roads on wildlife (adapted from Iuell 2005)
• Figure 19. Photo. Benavente, Spain. Highly fragmented landscape (high contrast; adapted from Google Earth)
• Figure 20. Photo. Hwy 101, Redwood highway, California. Low contrast landscape with low level of habitat fragmentation (adapted from Google Earth)
• Figure 21. Chart. Criteria for selecting general wildlife crossing type where roads bisect habitats of high conservation value
• Figure 22. Chart. Criteria for selecting general wildlife crossing type where roads bisect habitats of moderate conservation value
• Figure 23. Chart. Criteria for selecting general wildlife crossing type where roads bisect habitats of low conservation value
• Figure 24. Schematic. Four general types of topography where wildlife crossings maybe constructed on roadways (Credit: Tony Clevenger)
• Figure 25. Schematic. Length and width measurements of wildlife overpass (Credit: Tony Clevenger)
• Figure 26. Photo. Width and height measurements of wildlife underpass structure (Credit: Marcel Huijser/WTI)
• Figure 27. Photo. Most wildlife overpasses or landscape bridges are less than 70-80 m long; however, the one shown above near Hilversum, The Netherlands, is 800 m long and spans two roads and a railroad. (Credit: Goois Natuurreservaat, The Netherlands/Photo: W. Metz)
• Figure 28. Photo. Crossing structures are site-specific movement corridors that link wildlife habitat separated by pavement and high-speed vehicles (Credit: Jeff Stetz)
• Figure 29. Photo. Landscape bridge (Credit: Anonymous)
• Figure 30. Photo. Closure signage (Credit: Tony Clevenger)
• Figure 31. Photo. Brush piles on wildlife overpass (Credit: Tony Clevenger)
• Figure 32. Photo. Constructed amphibian habitat on edge of wildlife overpass (Credit: Tony Clevenger)
• Figure 33. Photo. Recently completed but unlandscaped wildlife overpass (Credit: Tony Clevenger)
• Figure 34. Photo. Berm on wildlife overpass (Credit: Tony Clevenger)
• Figure 35. Schematic. (A) Parabolic-shaped design overpass (B) Straight-edged design
• Figure 36. Photo. Human use lane and vegetated strip on multi-use overpass (Credit: Marcel Huijser)
• Figure 37. Photo. Canopy crossing installed in permanent signage fixture (Credit: Tony Clevenger)
• Figure 38. Photo. Ropes extending out from canopy crossing to forest canopy (Credit: Tony Clevenger)
• Figure 39. Photo. Viaduct as wildlife underpass (Credit: Ministère des Transports du Québec)
• Figure 40. Photo. Wide span viaduct designed to conserve floodplain (Credit: Tony Clevenger)
• Figure 41. Photo. Viaduct with retention of riparian vegetation (Credit: Tony Clevenger)
• Figure 42. Photo. "Stepping stone" ponds on wildlife overpass used to assist amphibian movement (Credit: Tony Clevenger)
• Figure 43. Photo. Open span wildlife underpass (Credit: Tony Clevenger)
• Figure 44. Photo. Brush and root wads placed along underpass wall to provide cover for mammals (Credit: Nancy Newhouse)
• Figure 45. Photo. Multi-use underpass in The Netherlands retrofitted for human use and wildlife passage (Credit: Marcel Huijser)
• Figure 46. Photo. Wildlife underpass designed to accommodate waterflow (Credit: Tony Clevenger)
• Figure 47. Photo. Mechanically stabilized earth (MSE) wall serving as wildlife exclusion "fence" (Credit: Tony Clevenger)
• Figure 48. Photo. Pipes placed in culverts to provide cover for small mammal movement (Credit: Tony Clevenger)
• Figure 49. Photo. Small- to medium-sized mammal underpass (Credit: Tony Clevenger)
• Figure 50. Photo. Continuous wildlife underpass on divided highway (Credit: Tony Clevenger)
• Figure 51. Photo. American marten using a drainage culvert to cross the Trans-Canada Highway, Banff National Park, Alberta (Credit: Tony Clevenger)
• Figure 52. Photo. Badger tunnel in The Netherlands (Credit: Tony Clevenger)
• Figure 53. Schematic. Technical design plan for artificial kit fox den in culvert (Credit: US Fish and Wildlife Service)
• Figure 54. Schematic. Modified culvert (Reprinted with permission from Kruidering et al. 2005)
• Figure 55. Photo. Construction and placement of amphibian tunnel in Waterton National Park, Alberta (Credit: Parks Canada)
• Figure 56. Photo. Drift fence for amphibians and reptiles (Credit: Tony Clevenger)
• Figure 57. Photo. Grated slots on amphibian tunnels allows light and conservers ambient temperatures and humidity (Credit: Anonymous)
• Figure 58. Photo. Flooding in front of tunnel due to improper drainage design (Credit: Tony Clevenger)
• Figure 59. Photo. Construction of amphibian ramp to replace curb and allow cross-road movement of long-toed salamanders (Credit: Parks Canada)
• Figure 60. Photo. Barrier or drift fence for amphibians and reptiles (Credit: Tony Clevenger)
• Figure 61. Photo. Drift fence and collection buckets (Credit: Tony Clevenger)
• Figure 62. Photo. Wildlife exclusion fencing and culvert design wildlife underpass (Credit: Tony Clevenger)
• Figure 63. Photo. Cattle guard (Texas gate) in road (Credit: Tony Clevenger)
• Figure 64. Photo. Step gate with spring-loaded door situated at trailhead in Banff National Park, Alberta (Credit: Tony Clevenger)
• Figure 65. Photo. Wildlife exclusion fence with buried apron (Credit: Tony Clevenger)
• Figure 66. Photo. Concrete base of swing gate to prevent animal digging under wildlife fence (Credit: Tony Clevenger)
• Figure 67. Photo. High tensile cable designed to break fall of trees onto fence material (Credit: Tony Clevenger)
• Figure 68. Photo. Warning signage at end of wildlife exclusion fence (Credit: Tony Clevenger)
• Figure 69. Photo. Boulder field at end of wildlife fence (Credit: Tony Clevenger)
• Figure 70. Photo. Small and medium-sized mammal fence material spliced to large mammal fence material (Credit: Nancy Newhouse)
• Figure 71. Photo. Escape ramp (jump-out) for wildlife trapped inside highway right-of-way (Credit: Tony Clevenger)
• Figure 72. Photo. Single swing gate in wildlife exclusion fence (Credit: Tony Clevenger)
• Figure 73. Photo. Wildlife escape ramp (jump-out; Credit: Tony Clevenger)
• Figure 74. Photo. Hinged door for escape of medium-sized mammals (Credit: Tony Clevenger)
• Figure 75. Photo. Remote digital infrared-operated camera (Credit: Tony Clevenger/WTI)
• Figure 76. Photo. Raking of track bed in culvert Banff National Park, Alberta (Credit: Tony Clevenger/WTI)
• Figure 77. Photo. Sooted track plate with tracks of small and medium-sized mammals (Credit: Robert Long/WTI)
• Figure 78. Schematic. Diagram of hair-snagging system at a wildlife underpass used in DNA- based research of population-level benefits of crossing structures (Source: Tony Clevenger/WTI)
• Figure 79. Photo. Grizzly bear passing through hair-snagging device at wildlife overpass in Banff National Park, Alberta (Credit: Tony Clevenger/WTI)
• Figure 80. Photo. Digital barcode tag for frogs (Source: Steve Wagner/CWU)
• Figure 81. Photo. Scat-detection dog working to locate scat (Credit: Robert Long/WTI)
• Figure 82. Photo. Roadkill Observation Collection System (ROCS) (Credit: WTI)

LIST OF TABLES

• Table 1. Data layers and maps for planning wildlife connectivity and crossing mitigation
• Table 2. Average spacing interval per mile between wildlife crossings designed for large mammals at existing and planned transportation projects
• Table 3. General guidelines for minimum and recommended dimensions of wildlife overpass designs
• Table 4. General guidelines for minimum and recommended dimensions of wildlife underpass designs
• Table 5. Suitability of wildlife crossing design types from Appendix C, Hot Sheets 1-11 for distinct wildlife species and taxa
• Table 6. Levels of conservation value for wildlife crossing systems as measured by ecosystem function achieved, level of biological organization targeted, type of connectivity potential, and cost and duration of research required to evaluate status
• Table 7. Guide to selecting focal species based on monitoring criteria and ecosystem context. 73 Table 8. Summary of available monitoring methods, the appropriate time to employ them (pre- or post-construction), potential target species, and cost estimates for conducting wildlife monitoring. See Appendix E for detailed description of each monitoring method (From Clevenger et al. 2008)

Acknowledgments

The author wishes to thank Roger Surdahl of the FHWA-CFLHD for the sponsorship and leadership.

For their help in promoting the survey, the author thanks Tina Barbaccia of Better Roads Magazine, Michele Beck of the Montana Local Technical Assistance Program (LTAP), Lorie Cover of the Idaho Technology Transfer (T2) Center, Mike Fitch of the Ohio Department of Transportation, Anthony Giancola of the National Association of County Engineers, John Kiefer of Michigan LTAP, Terry McNinch of Michigan LTAP, Russell Merle Jr. of the Clark County Department of Air Quality & Environmental Management, David Page of the Florida T2 Center, Carrie Plasters of EnviroTech Services, Dan Ratermann of the Missouri Association of County Transportation Officials, Bob Raths of the Association of Oregon Counties, Richard Rolland of the Tribal Technical Assistance Program, Mike Long, Chairman of the Transportation Research Board's Low-Volume Roads Committee, and others who may have regretfully been missed. The author is also very grateful to everyone who took the time to participate in the survey.

Finally, thanks to the staff at the Western Transportation Institute for their administrative support.

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