Action: Install culverts or tunnels as road crossings
Key messagesRead our guidance on Key messages before continuing
- Thirty-two studies investigated the effectiveness of installing culverts or tunnels as road crossings for amphibians.
- Six of seven studies (including three replicated studies) in Canada, Germany, Italy, Hungary and the USA found that installing culverts or tunnels significantly decreased amphibian road deaths; in one study this was the case only when barrier fencing was also installed. One found no effect on road deaths.
- Fifteen of 24 studies (including one review and 17 replicated studies) in Australia, Canada, Europe and the USA found that culverts/tunnels were used by amphibians, by 15–85% of amphibians or 3–15 species, or that 23–100% of culverts or tunnels were used by amphibians or used in 12 of 14 studies reviewed. The majority of culverts/tunnels had barrier fencing to guide amphibians to entrances. Four found mixed effects depending on species, or for toads depending on the site or culvert type. Five found that culverts were used by less than 10% of amphibians or were not used. The use of culverts/tunnels was affected by diameter in three of six studies, with wider culverts used more, length in one of two studies, with long culverts avoided, lighting in all three studies, with mixed effects, substrate in three of six studies, with natural substrates used more, presence of water in two of three studies, with mixed effects, entrance location in one and tunnel climate in one study.
- Six studies (including one replicated, controlled study) in Canada, Spain, the Netherlands and USA investigated the use of culverts with flowing water and found that they were used by amphibians, or rarely used by salamanders or not used, and were used more or the same amount as dry culverts.
- Certain culvert designs were not suitable for amphibians; one-way tunnels with vertical entry chutes resulted in high mortality of common toads and condensation deposits from steel culverts had very high metal concentrations. One study found that thousands of amphibians were still killed on the road.
Roads and traffic can have major impacts on amphibian populations. This is particularly the case if they cut across annual migration routes between hibernation and breeding habitats. Underpasses can be installed to try to reduce mortality on the road. Unlike methods such as toad patrols and road closures, which tend to target breeding adults, tunnels could help reduce deaths of dispersing juveniles. Tunnels may be designed specifically for amphibian migrations, wildlife pipes over land, wildlife culverts over water channels designed for small- to medium-sized animals or drainage culverts that were engineered for water passage, but that can be modified to encourage wildlife passage.
Culverts or tunnels are usually associated with barrier walls that prevent amphibians reaching the road and direct them towards tunnels. Studies that specifically investigated the effect of barrier fencing along roads are discussed in ‘Install barrier fencing along roads’.
Supporting evidence from individual studies
A study in 1983–1984 of a tunnel with guide fencing in Oberbergischer Kreis, Germany (Karthaus 1985) found that 640 common toads Bufo bufo and four frogs migrated through the tunnel. Overall, 85% of adult and 90% of young migrating toads used the tunnel, a nearby brook pipe, footpath or bridge to get across the road. However, on one night thousands of young toads were killed on the road. The tunnel was 19 m long and 0.75 m high and was completed in March 1984. A fence was constructed to direct amphibians to the tunnel. Monitoring was undertaken using pitfall traps at the ends of the tunnel and by observing toads during the migration.
A study in 1982–1989 of a tunnel under a road through woodland in Schleswig Holstein province, Germany (Brehm 1989) found that 21% of amphibians recorded along the drift-fencing used the tunnel. In 1988, a total of 2,446 amphibians were recorded along the fence, of which 21% passed through the tunnel. Seven species were recorded using the tunnel. For the four species for which more than 10 individuals were recorded (136–1278/species) 12–45% passed through the tunnel. The tunnel was installed in 1987 (0.2 m diameter, 10 m long). Drift-fencing 360 m long and 0.4 m high already existed at the site. Amphibians were monitored using 28 pitfall traps along the fence and one at the tunnel exit.
A study in 1984–1985 of a tunnel with barrier fencing in Lower Saxony, Germany (Buck-Dobrick & Dobrick 1989) found that only 15% of amphibians recorded entered the tunnel and few passed through the tunnel. It was considered that this may have been due to high water levels which resulted in a stream flowing through the tunnel. Fences 350 m long were installed on both sides of the road. The concrete tunnel was located in the centre of the fences. Common toads Bufo bufo and common frogs Rana temporaria were monitored in March–April. Toads were tagged.
A replicated study in 1987 of tunnels with guide fencing at 13 locations in West Germany (Dexel 1989) found that tunnel use by amphibians varied with site. Some tunnels were not used by amphibians while others were used by the majority of migrating amphibians. Large two-way tunnels (diameter: 1 m; length: 15 m) were used by a larger proportion of common toads Bufo bufo in the area than those with smaller diameters. However, even those with a diameter of 0.3 m were used by some toads. One-way tunnels with vertical entry chutes resulted in high mortality of amphibians. There were no deaths with angled chutes. Three types of tunnels were investigated: two-way systems or one-way systems with angled or vertical entry chutes. One-way tunnels were laid in pairs to allow migration in both directions. At one site, nine two-way systems of various dimensions were investigated. Guide fences were also used at sites.
A replicated study in 1980–1988 of eight tunnels with barrier fencing in Bavaria, West Germany (Haslinger 1989) found that common toads Bufo bufo did not use the tunnels. Tunnels were 60 cm in diameter. Wire-netting fences 25 cm high were installed on both sides of the road. Fences were bent over at the top to prevent toads climbing over.
A small, replicated study in 1987 of two tunnels with barrier fencing in Henley-on-Thames, England, UK (Langton 1989) found that approximately 2,750 common toads Bufo bufo used the tunnels during 18 migration nights. In the first two nights, only about 10% of 2,200 toads recorded behind the fence were estimated to have used the tunnels. This increased to a maximum of 43% of toads recorded in one night. Fencing was installed between the two tunnels creating a W-shaped catchment of 600 m. A trip counter was set 0.2 m into the entrance of the tunnels.
A small, replicated study in 1987–1988 of two amphibian tunnels with barrier fencing in the Mittelgebirge region of West Germany (Meinig 1989) found that once an effective fence was installed, 85% of amphibians recorded used the tunnels and road deaths decreased. Prior to the new fence, numbers killed were 109/night, compared to just 20 in 1987 and 30 in 1988. Between 2,432 and 2,050 individuals/year were captured at the fence and surroundings during the spring migration, of which 85% used the tunnels. Of 211 toads marked at the fence in 1987, 68% were recaptured at tunnel exits within five days. Two drain channels with metal grid roofs were installed in the road in 1981. A more effective fence of plastic fabric similar to wire mesh (1 m high) was installed at entrances and parallel to the road in 1987. Pitfall traps were set at each end of the fence and at tunnel exits.
A replicated study of five amphibian tunnels with barrier fencing in Overveen in the Netherlands (Zuiderwijk 1989) found that only 4% of the population of 2,000–3,000 common toads Bufo bufo used the tunnels. Ten percent of the population broke over the barrier fencing. The remaining toads walked along the fence, were captured in pitfall traps and were carried across the road. In an experiment, toads were placed at tunnel entrances and 43% passed through within 24 hours. The cast-iron tunnels had been installed nine years before the study. They were 12 m long, 0.3 m in diameter and were buried 0.7 m under a road between a wooded dune and stream. The road had permanent barrier fencing.
A replicated study in 1993 of 17 culverts in Madrid province, Spain (Yanes, Velasco & Suarez 1995) found that amphibians used the culverts. An average of 0.03 amphibian tracks/culvert/day (range: 0–0.19) were recorded. Two culverts were selected under a motorway, 10 under local roads and five under a railway line. Amphibian tracks were monitored within culverts using marble dust over the floor. Monitoring was undertaken over four to eight days each season.
A small, replicated study in 1988 of two amphibian tunnels under a road in Amherst, Massachusetts, USA (Jackson 1996) found that 76% of spotted salamanders Ambystoma maculatum that reached tunnel entrances successfully passed through (n = 87). Of the salamanders recorded along fences 68% (n = 95) passed through tunnels. Salamanders that encountered fences furthest from the tunnels were reached tunnels as successfully as those that encountered the fence closer to the entrances. Once artificial light was provided, salamanders entered and passed through tunnels faster. Tunnels were installed approximately 60 m apart with 30 m long (0.3 m high) drift-fences to direct salamanders to the entrances. Tunnels allowed some rain to enter to maintain moist conditions, but were prevented from flooding. Tunnels and fences were monitored by observations on four nights during spring 1988.
A replicated, site comparison study in 1993–1994 of 56 tunnels under roads in Catalonia, Spain (Rosell et al. 1997) found that amphibians used 23% of circular and 59% of rectangular tunnels. Use was greater for wider tunnels with water within or at entrances. Tunnels with steps or wells at the entrances or within large embankments were used less frequently. A total of 39 circular (1–3 m diameter) and 17 rectangular cross-section (4–12 m diameter) drains/underpasses were surveyed along four 10 km stretches of roads. Tunnels were monitored for four days each season over a year in 1993–1994. Tracks were obtained using marble power across the centre of each structure. Infra-red and photographic cameras were used at entrances.
A replicated study in 1997–1998 of 53 wildlife passages along waterways under roads at over 20 sites in the Netherlands (Veenbaas & Brandjes 1999) found that 77% of passages were used by amphibians. Amphibian tracks were recorded in 19–22 passages/year. There was no relationship between use and passage width or substrate. Culverts and bridges were adapted for wildlife in the 1990s in the Netherlands. In 1997, 31 passages (0.4–3.5 m wide) were monitored. These included extended banks (unpaved or paved), planks fixed on bridge or culvert walls, planks floating on the water, concrete passageways and plastic gutters covered with sand. In 1998, 22 passages were monitored for the effect of width and substrate. These were wooden passageways fixed on a bridge or culvert wall (0.2–0.6 m wide). Monitoring involved weekly checks of tracks on sandbeds (for 4–7 weeks) and ink pads (12 weeks in 1997, four weeks in 1998) across passageways.
A replicated study in 2000 of eight dry and two wet culverts under highways through two wetlands on Vancouver Island, Canada (Fitzgibbon 2001) found no amphibian tracks within culverts. In trials with rough-skinned newts Taricha granulosa, a dark culvert was used significantly more than one with daylight (24 vs 6). However, there was no significant difference between use of 0.3 or 0.5 m diameter culverts (11 vs 19 newts), different substrates (bare: 22; cement: 11; soil: 17) or wet or dry culverts (8 vs 7–15 newts). Concentrations of aluminium, zinc, copper and lead within condensation deposits in culverts were 134–124,500 times greater than recommended for protecting freshwater aquatic life. Corrugated steel pipe culverts (29–36 x 0.6–1 m) were constructed in 1995. Aluminium track-plates covered with soot were installed 1–2 m inside each culvert and were monitored nine times in July–October 2000. There were three replicates of each trial (five for substrate) in which 10 newts had the choice of three adjacent culverts (3 x 0.3 m) over three days in September–November.
A small, replicated study in 2000–2001 of two amphibian tunnels constructed under a road in a residential development in Santa Cruz County, California, USA (Allaback & Laabs 2002-2003) found that a small proportion of migrating Santa Cruz long-toed salamanders Ambystoma macrodactylum croceum used tunnels. A total of 23 adult salamanders passed through the tunnels. Of the 44 adults marked along the drift-fence, only four (9%) were captured on the opposite side of one tunnel and none for the other. The two cement polymer amphibian tunnels were installed in 1999. They were 0.3 x 0.5 m or 0.2 x 0.2 m and 11–12 m long. Entrances were screened with mesh to reduce predator access. Drift-fences (0.4–0.8 m high) were permanently installed at tunnel entrances and along the road to connect tunnels (300 m). Salamanders were monitored by visual survey along the drift-fence on five rainy nights in December–January. Each animal was marked. Pitfall traps captured individuals passing through tunnels.
A replicated study in 1998 of 38 amphibian tunnels at 16 sites, two game bridges and five game passages in northern Hungary (Puky & Vogel 2003) found that 11 amphibian species used the passageways. Some of the passageways were used successfully and others had efficiency below 25%. Problems were considered to include improper design, gaps between the fence and entrance and lack of fencing or maintenance. Population estimates suggested that the mitigation measures helped 1 million to 5 million amphibians across roads annually. Tunnels were circular or square, made of concrete or metal and had diameters of 0.6–1.0 m. Concrete or mesh fences (0.5–0.7 m high) were present in 80% of cases. Day and night road transects were undertaken during spring and summer to count live and dead amphibians. Population sizes in neighbouring habitats were estimated using visual encounter surveys, torching and netting, acoustic surveys and transect counts.
A replicated study in 2000–2001 of nine wildlife culverts with barrier fencing along a highway through coastal lowlands in New South Wales, Australia (Taylor & Goldingay 2003) found that all culverts were used by amphibians. Amphibian tracks made up 14% of those in culverts. Cane toads Bufo marinus were observed inside culverts nine times. Twelve additional species were recorded within 2–20 m of entrances. Fifty-five frog (brown-striped frog Limnodynastes peronii, dainty green tree frog Litoria gracilenta) and two cane toad carcasses and 14 live frogs were recorded on the road on one night. The concrete culverts (2.4 m wide, 1.2 m high, 18 m long) lay along a 1.4 km section of highway. A chain-mesh barrier fence (1.8 m high) was installed either side of the bypass. Each culvert was walked through with a spotlight on two wet and two dry nights in January-February 2001. Tracks were recorded on sand across culverts every two days over eight days in spring and autumn. Frog calls were also recorded at entrances.
A replicated study in 2001–2002 of eight culverts underneath a highway through a freshwater marsh in Florida, USA (Dodd, Barichivich & Smith 2004) found that 13 frog and two salamander species used culverts and road mortality declined. A total of 656 frogs and six salamanders were captured using culverts. Following construction of a barrier wall linking culverts, frog species using culverts increased from five to 13 and frogs trapped increased from 0.006 to 0.085/trap night. Ranid frog mortality declined dramatically following installation of the barrier wall-culvert system. However, tree frog mortality appeared to increase (from 149 to 194). Two dry box culverts (1.8 x 1.8 x 44 m) and two partially submerged box culverts (2.4 x 2.4 x 44 m) already existed. In 2001, four additional dry/wet cylindrical culverts (0.9 x 44 m) were installed at the same time as a 3 km barrier wall along the highway, parallel to wetland prairie. Culverts were 200–500 m apart along the wall. Monitoring was undertaken on five nights/week from March 2001 to March 2002. Ten wire screen-mesh funnel traps were placed in each box culvert and four crayfish traps in each cylindrical culvert.
A review of studies investigating culverts in Texas and near New York, USA (Jochimsen et al. 2004) found mixed results. Two tunnels with barrier walls decreased amphibian road deaths by 90%. Eight of the 20 known species were recorded using the tunnels. In contrast, no Houston toads Bufo houstonensis used modified drainage culverts and athough diversion fencing reduced road-kills in its vicinity, groups of dead toads were recorded at the ends. Short sections of steel diversion fencing were added to existing drainage culverts to guide toads from known migration routes into the culverts. The culverts were not designed for amphibians and became impassable when flooded. Two concrete tunnels with box openings (1.2 x 1.2 m) and wooden barrier walls were installed along a road adjacent to wetlands in 1999.
A replicated study in 2001, of two experimental tunnels in Pays de la Loire, France (Lesbarrères, Lodé & Merilä 2004) found that amphibians used tunnels and preferred the soil-lined to the bare tunnel. Tunnels were preferred to bypassing on the grass by common toads Bufo bufo (70%) and edible frogs Rana esculenta (68%). However, agile frogs Rana dalmatina tended to bypass (70%). The soil-lined tunnel was used by 68% of the animals that used the tunnels. The difference between soil-lined and bare tunnels was significant for both frog species but not common toads. Crossing success was higher for all species in the soil-lined tunnel. Two concrete pipes (2 m long, 0.5 m diameter) were placed side by side within an enclosure (5 x 3 m). One was lined with sand and humus, the other left bare. Two 0.5 m lengths of drift-fence were installed at 45° to the entrances. A single animal was placed 1.2 m in front of the tunnels with male calls playing from the far end. Each trial lasted 10 minutes and was repeated four days later. Forty-one common toads, 42 edible frogs and 32 agile frogs captured locally were used.
A replicated, controlled study in 2002–2003 of culverts along small forest streams in the Oregon Coast Range, USA (Sagar 2004, Sagar, Olson & Schmitz 2007) found that culverts were used by a small proportion of larval coastal giant salamander Dicamptodon tenebrosus. Complete culvert passage was recorded by 16 larvae at seven of nine culvert sites, although only 20% of larvae moved far enough to assess culvert passage. Growth rates and density did not differ significantly, but movements varied in streams with and without culverts. Effects on larval survival were inconclusive. Densities were lower in raised metal pipe culverts than in arch culverts with streambed substrates. Arch culverts and streams had similar densities. Density was associated with the presence of large substrates. In the presence of culverts, the direction and distance moved did not differ significantly (culvert: 3 m; none: 4 m), but larvae moved to the centre of the stream section less frequently. Nine sites with a culvert (four pipe and five arch) and five without were selected. Stream sections (80 m long) and culverts were monitored two to three times in June–August using dip-netting and visual surveys. Culverts were located at the centre of each section. A total of 2,215 larvae were measured and marked.
A study in 2000–2003 of a culvert under a highway by Lake Jackson, Florida, USA (Aresco 2005) found that at least three amphibian species used the culvert. Many leopard frog Rana sphenocephala, pig frog Rana grylio and American bullfrog Rana catesbeiana were observed moving through the culvert. In total, 12 amphibian species were recorded along the fence and road. A temporary fence was installed along the highway to divert animals to an existing metal drainage culvert in April 2000 (700 m; 0.4 m high) and September 2000 (600 m). Monitoring was undertaken 1–4 times daily by walking the fence and checking the road and culvert until November 2003.
A replicated study in 2003–2005 of five amphibian tunnels with guide fencing along a road through Oak Ridges Moraine in Ontario, Canada (Gartshore et al. 2006) found that four of the tunnels were used by amphibians but not by the targeted Jefferson salamander Ambystoma jeffersonianum. Tunnels were used by a small number of amphibians in 2003, when weather conditions minimized activity. In 2004, 22 amphibians were recorded in or near tunnels. American toad Bufo americanus, wood frog Rana sylvatica, spring peeper Pseudacris crucifer and leopard frog Rana pipiens, but not spotted salamander Ambystoma maculatum or Jefferson salamander were recorded. Observations were evenly spread across four tunnels, the fifth was waterlogged. Five concrete or steel tunnels, 1.2 m diameter and 25–31 m long, were installed under a new road section in 2001. Each was lined with a sandy substrate and had 30–50 m of guide fencing on each side. Six to eight monitoring visits were undertaken each spring in 2003–2004. Plastic fences directed amphibians to pitfall traps at the tunnel entrances and exits. Fences were also walked by observers at night.
A before-and-after study in 1994–2004 of a brackish and freshwater wetland in southern Tuscany, Italy (Scoccianti 2006) found that raising a road on a viaduct resulted in a significant decrease in amphibian road deaths. Following construction, no remains of amphibians were found on the road, compared to thousands during some periods pre-construction. For example, after a night rainstorm in July 1997, over 6,500 newly emerged Italian edible frog Rana hispanica juveniles were counted on a 100 m stretch of road. Many species used the open space under the viaduct to migrate between wetlands. A viaduct 215 m long was constructed in 2003 to raise a road. The supports of the viaduct (1.6 m high) were built on a bank 1 m higher than potential flood waters to prevent mixing of wetlands. Drift-fencing was installed for 300 m from each end of the viaduct along both sides of the road. Amphibian road kills were monitored before and after construction.
A study in 2004–2008 of a culvert with barrier wall along a new highway through upland forest in New Hampshire, USA (Merrow 2007) found no evidence that it had been used by amphibians during the first three years. A ‘wildlife diversion wall’ preventing access to the road and funnelling animals to the culvert did divert amphibians. Small numbers of spotted salamanders Ambystoma maculatum and wood frogs Rana sylvatica were found moving along the wall. However, small numbers of these species were found crossing the road in areas without a wall or culvert. The culvert was constructed near to the most productive pond for amphibians. It was 17 m long with an opening 1.2 x 1.2 m. Loamy soil material was used and was sloped across the width of the culvert to confine stream flow to one side. The diversion wall (0.3 m high) extended from the culvert to a stone-lined stream channel on one side and a larger pedestrian culvert on the other. Spring amphibian migrations were monitored for three years after construction.
A replicated study in 2005–2006 of tunnels in a Wildlife Management Area in New York, USA (Woltz, Gibbs & Ducey 2008) found that green frogs Rana clamitans and leopard frogs Rana pipiens showed some preference for particular tunnel types. Green frogs showed a significant preference for soil (40%) and gravel (38%) linings, compared to concrete (13%) and PVC (9%). Leopard frogs showed no preference (19%, 32%, 29%, 19% respectively). Leopard frogs tended to prefer larger diameters (0.8 m: 35%; 0.6 m: 12%; 0.5 m: 28%; 0.3 m: 25%) and avoid the longest tunnels (9 m: 15%; 6 m: 40%; 3 m: 22–24%). Green frogs showed no preference for diameter (0.8 m: 33%; 0.6 m: 24%; 0.5 m: 27%; 0.3 m: 16%) or length (9 m: 32%; 6 m: 23%; 3 m: 19–26%). Tunnels with the greatest light permeability were preferred (4% light permeability: 39–41%; 1.3% light: 14–17%; 0.6% light: 24–26%; no light: 17–24%). Choice arenas had four different PVC culverts radiating out, which local green frogs (n = 135) and leopard frogs (187) could select to exit through. Frogs were tested in groups of 1–17 individuals, once per arena. Trials lasted 15 minutes, after 5 minutes acclimatization, in June–August 2005–2006. Pitfall traps captured animals at the end of each tunnel.
A replicated study in 2008 of different culvert designs in New York State, USA (Patrick et al. 2010) found that migrating spotted salamanders Ambystoma maculatum showed no preference for culverts of particular diameters, length or substrate. However, the concrete-lined culvert was used significantly less than other substrates (concrete: 28%; bare: 35%; sand/gravel: 37%). There was no significant difference in use of culverts of different diameters (0.3 m: 28%; 0.6 m: 33%; 0.9 m: 39%) or lengths (3 m: 30%; 6 m: 32%; 9 m: 39%). Spotted salamanders and American toads Anaxyrus americanus did not show a strong preference for crossing near existing culverts under the highway. The four test areas were 30–100 m apart, alongside a highway in a forested wetland. Each consisted of two 9 m long fences (1 m high) that funnelled animals towards three choices of PVC culverts. A pitfall trap captured migrating animals at the end of each culvert. A total of 57–139 salamanders were captured per test area. Sampling was undertaken during five nights in March–April 2008.
A review in 2010 of studies monitoring 327 road crossing structures in Australia, Europe and North America (Taylor & Goldingay 2010) found that amphibians used crossing structures in 12 of 14 studies. Amphibians used drainage culverts in four of five studies, adapted culverts in all three studies and pipes in both studies they were monitored. Wildlife underpasses, bridge underpasses and overpasses were used in the one study that monitored each. Amphibians did not use the one wildlife overpass monitored. Fourteen of the 30 published papers investigated multiple structure types, which resulted in a total of 52 studies of different structure types.
A controlled study in 2009 of wildlife culverts along a new highway through wetlands near Whistler, Canada (Malt 2011) found that road-kill rates were reduced provided that drift-fencing or barriers were installed to direct animals towards culverts. Road-kill rates were reduced significantly (by over 50%) along road sections with ≥ 50 m of drift-fencing or barriers compared to those with no barriers (2–8 vs 15–17 killed/50 m section). Approximately 400–500 amphibians were still killed annually along the new highway. Amphibians appeared hesitant to use culverts. Eight wildlife culvert underpasses were constructed along the section through the wetland. Drift-fences were installed to funnel animals towards culverts. Barrier walls were also installed to prevent migration along some sections. Amphibians were monitored using roadkill surveys, remote cameras at culvert entrances and a mark‐recapture study of red‐legged frogs Rana aurora.
A small, replicated study in 2009 of four amphibian tunnels in Waterton Lakes National Park, Alberta, Canada (Pagnucco, Paszkowski & Scrimgeour 2011) found that 8% of the estimated breeding population of long-toed salamanders Ambystoma macrodactylum used the tunnels. A total of 104 salamanders were captured in pitfall traps and at least another 26 by cameras in tunnels. Five western toad Anaxyrus boreas and seven barred tiger salamander Ambystoma mavortium were also recorded in the tunnels. Only one case of snake predation was recorded by cameras. Four concrete tunnels were installed 80–110 m apart under the road (0.6 x 0.5 m, 12 m long). Digital cameras were installed on the ceilings of tunnel entrances to monitor tunnel floors with motion-triggered and timed-interval images. One pitfall trap was installed at each tunnel exit in April–August.
A replicated study in 2011–2012 of 26 wildlife tunnels with guide walls at three wetland sites on the Great Hungarian Plain, Hungary (Faggyas & Puky 2012) found that amphibians used the tunnels in large numbers in the first year. Between 120 and 1,800 amphibians were caught at the end of each tunnel over two weeks. European fire-bellied toads Bombina bombina and the targeted spadefoot toad Pelobates fuscus were recorded in highest numbers. The Danube crested newt Triturus dobrogicus, a priority conservation species, also used the tunnels. At one site, ten times more amphibians passed through two new climate tunnels than an existing adjacent concrete culvert. A total of 26 polymer concrete ACO Wildlife Pro climate tunnels, guide walls (300–600 m/tunnel) and stop channels (under side roads that bisected guide walls) were constructed under three roads in autumn 2011. Amphibians were monitored using nine pitfall traps/road in April 2012.
A before-and-after study in 2006–2011 of a tunnel with barrier wall along a road in Hungary (Mechura et al. 2012) found that up to 15% of migrating amphibians used the tunnels but road deaths did not decrease significantly. During the two years after construction, there was no significant reduction in road deaths as fewer than 1% of migrating amphibians used the tunnels. Following maintenance, over the next three years 9–15% of the amphibians used the tunnels. However, over 10,000 amphibians died on the road section each year in 2009–2011 even although toad rescue was also carried out by volunteers. Seven frog and toad species and two newt species were recorded dead along the road. Almost 90% were common toads Bufo bufo. In 2006 a tunnel with barrier system was constructed for amphibians between Hont and Parassapuszta. Maintenance was undertaken in spring 2009 and in 2010 and 2011.
A before-and-after study in 2008–2009 of four amphibian tunnels under a road parallel to a lake in Alberta, Canada (Pagnucco, Paszkowski & Scrimgeour 2012) found that tunnels were effective at reducing road mortality of long-toed salamanders Ambystoma macrodactylum. Road mortality decreased from 10% of the population in 1994 to 2% following installation. In 2009, 104 salamanders were recorded using tunnels, 74% were migrating to the lake. Four gray tiger salamanders Ambystoma mavortium and seven western toads Anaxyrus boreas were also captured in exit traps. Individual tunnel use differed (7–49%). In May 2008, four concrete box culverts (0.6 x 0.5 m) were installed for amphibians 80–110 m apart. They had slots to allow air, moisture and light in. Drift-fences 500 m long were installed either side of the road with pitfall traps checked daily in April–October 2008. In 2009, additional fences (133–274 m) were installed to direct salamanders to tunnels and pitfalls were installed at exits. Road mortality surveys (similar to 1994) and fence surveys were undertaken daily in 2008 and May–June 2009.
- Karthaus G. (1985) Schutzmaßnahmen für wandernde amphibien vor einer gefährdung durch den Staßenverkehr - beobachtungen und erfahrungen. Natur und Landschaft, 60, 242-247
- Brehm K. (1989) The acceptance of 0.2-metre tunnels by amphibians during their migration to the breeding site. Amphibians and Roads: Proceedings of the Toad Tunnel Conference, Rendsburg, Federal Republic of Germany, 29-42.
- Buck-Dobrick T. & Dobrick R. (1989) The behaviour of migrating anurans at a tunnel and fence system. Amphibians and Roads: Proceedings of the Toad Tunnel Conference, Rendsburg, Federal Republic of Germany, 137-143.
- Dexel R. (1989) Investigations into the protection of migrant amphibians from the threats from road traffic in the Federal Republic of Germany - a summary. Amphibians and Roads: Proceedings of the Toad Tunnel Conference, Rendsburg, Federal Republic of Germany, 43-49.
- Haslinger H. (1989) Migration of toads during the spawning season at Stallauer Weiher lake, Bad Tölz, Bavaria. Amphibians and Roads: Proceedings of the Toad Tunnel Conference, Rendsburg, Federal Republic of Germany, 181-182.
- Langton T.E.S. (1989) Tunnels and temperature: results from a study of a drift fence and tunnel system for amphibians at Henley-on-Thames, Buckinghamshire, England. Amphibians and Roads: Proceedings of the Toad Tunnel Conference, Rendsburg, Federal Republic of Germany, 145-152.
- Meinig H. (1989) Experience and problems with a toad tunnel system in the Mittelgebirge region of West Germany. Amphibians and Roads: Proceedings of the Toad Tunnel Conference, Rendsburg, Federal Republic of Germany, 59-66.
- Zuiderwijk A. (1989) Amphibian and reptile tunnels in the Netherlands. Amphibians and Roads: Proceedings of the Toad Tunnel Conference, Rendsburg, Federal Republic of Germany, 67-74.
- Yanes M., Velasco J.M. & Suarez F. (1995) Permeability of roads and railways to vertebrates: the importance of culverts. Biological Conservation, 71, 217-222
- Jackson S.D. (1996) Underpass systems for amphibians. Proceedings of the International Conference on Wildlife Ecology and Transportation, Florida Department of Transportation, Tallahassee, 240–244.
- Rosell C., Parpal J., Campeny R., Jove S., Pasquina A. & Velasco J.M. (1997) Mitigation of barrier effect on linear infrastructures on wildlife. Pages 367-372 in: Habitat Fragmentation & Infrastructure. Ministry of Transport, Public Works and Water Management, Delft, Netherlands.
- Veenbaas G. & Brandjes J. (1999) Use of fauna passages along waterways under highways. Proceedings of the International Conference on Wildlife Ecology and Transportation, Florida Department of Transportation, Tallahassee, 253–258.
- Fitzgibbon K. (2001) An evaluation of corrugated steel culverts as transit corridors for amphibians and small mammals at two Vancouver Island wetlands and comparative culvert trials. MA thesis. Royal Roads University.
- Allaback M.L. & Laabs D.M. (2002) Effectiveness of road tunnels for the Santa Cruz long-toed salamander. Transactions of the Western Section of the Wildlife Society, 38/39, 5-8
- Puky M. & Vogel Z. (2003) Amphibian mitigation measures on Hungarian roads: design, efficiency, problems and possible improvement, need for a co-ordinated European environmental education strategy. International Conference on Habitat Fragmentation due to Transportation Infrastructure, IENE, Brussels,
- Taylor B.D. & Goldingay R.L. (2003) Cutting the carnage: wildlife usage of road culverts in north-eastern New South Wales. Wildlife Research, 30, 529-537
- Dodd C.K., Barichivich W.J. & Smith L.L. (2004) Effectiveness of a barrier wall and culverts in reducing wildlife mortality on a heavily traveled highway in Florida. Biological Conservation, 118, 619-631
- Jochimsen D.M., Peterson C.R., Andrews K.M. & WhitfieldGibbons J. (2004) A literature review of the effects of roads on amphibians and reptiles and the measures used to minimize those effects. Idaho Fish and Game Department and USDA Forest Service report.
- Lesbarrères D., Lodé T. & Merilä J. (2004) What type of tunnel could reduce road kills? Oryx, 38, 220-223
- Sagar J.P., Olson D.H. & Schmitz R.A. (2007) Survival and growth of larval coastal giant salamanders (Dicamptodon tenebrosus) in streams in the oregon coast range. Copeia, 1, 123-130
- Aresco M.J. (2005) Mitigation measures to reduce highway mortality of turtles and other herpetofauna at a north Florida lake. Journal of Wildlife Management, 69, 549-560
- Gartshore R.G., Purchase M., Rook R.I. & Scott L. (2006) Bayview Avenue extension, Richmond Hill, Ontario, Canada habitat creation and wildlife crossings in a contentious environmental setting: a case study. Proceedings of the 2005 International Conference on Ecology and Transportation, Center for Transportation and the Environment, North Carolina State University, Raleigh, NC, 55-76.
- Scoccianti C. (2006) Rehabilitation of habitat connectivity between two important marsh areas divided by a major road with heavy traffic. Acta Herpetologica, 1, 77-79
- Merrow J. (2007) Effectiveness of amphibian mitigation measures along a new highway. Proceedings of the 2007 International Conference on Ecology and Transportation, Center for Transportation and the Environment, North Carolina State University, 370-376.
- Woltz H.W., Gibbs J.P. & Ducey P.K. (2008) Road crossing structures for amphibians and reptiles: informing design through behavioral analysis. Biological Conservation, 141, 2745-2750
- Patrick D.A., Schalk C.M., Gibbs J.P. & Woltz H.W. (2010) Effective culvert placement and design to facilitate passage of amphibians across roads. Journal of Herpetology, 44, 618-626
- Taylor B.D. & Goldingay R.L. (2010) Roads and wildlife: impacts, mitigation and implications for wildlife management in Australia. Wildlife Research, 37, 320-331
- Malt J. (2011) Assessing the effectiveness of amphibian mitigation on the Sea to Sky Highway: passageway use, roadkill mortality, and population level effects. Herpetofauna and Roads Workshop - Is there light at the end of the tunnel? Vancouver Island University, Nanaimo, Canada, 17-18.
- Pagnucco K.S., Paszkowski C.A. & Scrimgeour G.J. (2011) Using cameras to monitor tunnel use by long-toed salamanders (Ambystoma macrodactylum): an informative, cost-efficient technique. Herpetological Conservation and Biology, 6, 277-286
- Faggyas S. & Puky M. (2012) Construction and preliminary monitoring results of the first ACO Wildlife Pro amphibian mitigation systems on roads in Hungary. Állattani Közlemények, 97, 85–93
- Mechura T., Gémesi D, Szövényi G. & Puky M. (2012) Temporal characteristics of the spring amphibian migration and the use of the tunnel-barrier system along the Hont and Parassapuszta section of the main road No. 2. between 2009 and 2011. Állattani Közlemények, 97, 77–84
- Pagnucco K.S., Paszkowski C.A. & Scrimgeour G.J. (2012) Characterizing movement patterns and spatio-temporal use of under-road tunnels by long-toed salamanders in Waterton Lakes National Park, Canada. Copeia, 2012, 331-340