Effectiveness of a barrier wall and culverts in reducing wildlife mortality on a heavily traveled highway in Florida

Install barriers and crossing structures along roads/railways

A study in 2001–2002 along a highway in Florida, USA (Dodd et al. 2004) found that culverts, in areas with roadside barrier walls, were used by reptiles but road casualties still occurred. Seventeen reptile species were recorded using culverts. These included American alligators Alligator mississippiensis (in five culverts), four turtle species (four culverts), green anoles Anolis carolinensis (one culvert) and 11 snake species (seven culverts). During the same period, ≥22 reptile species were recorded dead on the road. The most frequent casualties were yellow ratsnake Elaphe obsolete (16 individuals), southern watersnake Nerodia fasciata (21), and DeKay’s brownsnake Storeria dekayi (54). Culverts reduced overall vertebrate road mortality, but separate reptile figures were not reported for before culverts were installed. Eight culverts (from 0.9 m diameter to 2.4 × 2.4 m cross-section, all 44 m long) were connected using prefabricated concrete barrier walls. Culverts were monitored from 14 March 2001 to 5 March 2002 using funnel traps, camera traps and sand track stations. Roadkills were monitored by walking the 3.2 km road over three consecutive days each week over the same period.

(Summarised by: Maggie Watson, Katie Sainsbury)

Install barrier fencing along roads

A controlled, before-and-after study in 2001–2002 of a barrier wall linking culverts along a highway in Florida, USA (Dodd, Barichivich & Smith 2004) found that the wall significantly decreased amphibian road deaths, apart from treefrogs (Hylidae), which could climb over. A total of 19 amphibian road-kills were found on the 3 km section with barrier, compared to 326 kills on the 500 m section with no barrier. Treefrogs were excluded from these figures. Treefrog mortality increased after construction of the barrier and culverts (from 149 to 194 over three survey sections). In 2001, a 1 m high concrete wall with a 15 cm overhang was erected along the highway, parallel to a wetland prairie. The wall extended 3 km on each side of the road. Concrete culverts under the highway were increased from four to eight. The highway and grass verge were monitored from 200 m before the start of the barrier until 200 m past the end. Monitoring was undertaken on three consecutive days from dawn each week from March 2001 to March 2002.

Install barrier fencing along roads

A controlled, before-and-after study in 1998–2002 along a highway in Florida, USA (Dodd et al. 2004) found that a barrier wall-culvert system reduced mammal road-kills. After construction, 33 mammals of ≥12 species were recorded dead on the 2.8-km section of road with the barrier (2.8 km) compared to 50 mammals on a 400-m section without barriers. Of those killed along the barrier, 17 were rice rats Orozomys palustris, which climbed adjacent vegetation to get over the barrier. In 2000–2001, a 1-m-high concrete wall with 15-cm overhanging lip was constructed along a 2.8-km section of a highway. Eight concrete culverts were spaced 200–500 m apart below the wall. Roadkills were monitored on three days/week before (August 1998–1999) and after (March 2001-March 2002) barrier wall construction.

(Summarised by: Rebecca K. Smith)

Install culverts or tunnels as road crossings

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.

Install barrier fencing and underpasses along roads

A study in 2001–2002 along a highway in Florida, USA (Dodd et al. 2004) found that culverts, in areas with roadside barrier walls, were used by mammals but road casualties still occurred. Ten mammal species (and one species pair) were recorded using culverts. These included rice rat/hispid cotton rat Oryzomys palustris/Sigmodon hispidus (in five culverts), cotton mouse Peromyscus gossypinus (three culverts), round-tailed muskrat Neofiber alleni (three culverts) and southeastern short-tailed shrew Blarina carolinensis (two culverts). Other species used one culvert each. During the same period, ≥13 mammal species were recorded dead on the road. The most frequent casualties were rice rat (25), Virginia opossum Didelphis virginianus (15) and nine-banded armadillo Dasypus novemcinctus (10). Culverts reduced overall vertebrate road mortality, but separate mammal figures were not reported for before culverts were installed. Eight culverts (from 0.9 m diameter to 2.4 × 2.4 m cross-section, all 44 m long) were connected using prefabricated concrete barrier walls. Culverts were monitored from 14 March 2001 to 5 March 2002 using funnel traps, camera traps and sand track stations. Roadkills were monitored by walking the 3.2-km road over three consecutive days each week.

(Summarised by: Rebecca K. Smith)