Bat bridge
A bat bridge is a structure of varying construction crossing a new or altered road to aid the navigation of bats following the destruction of a hedgerow, and to cause the bats to cross the roadway at a sufficient height to avoid traffic. Bats are thought to follow the lines of hedgerows and woods, and removing these may confuse the bats.
The theory is that these "bridges" will be seen by the bats' sonar as linear features sufficiently similar to the old hedgerows as to provide an adequate substitute. The Highways Agency is performing a study of those on the Dobwalls bypass to determine if this assumption is justified.
Usage
Bat structures in the UK
| Scheme Name | Road Number | Road Opened | Approx Length of Structure | Single or Dual Carriageway | Cutting/Embankment/At Grade | Approx Construction Cost of Structure | Other details |
| Stainburn and Great Clifton Bypass | A66 | December 2002 | Gantry | Single | |||
| High and Low Newton | A590 | April 2008 | 33 m span between timber supporting posts | Dual | In cutting | £45,000 | - |
| Dobwalls | A38 | June 2008 | Structure 1—59.47 m Structure 2—70 m | Dual | At Grade/In Cutting | £300,000 | These bridges are more elaborate and sophisticated than the earlier Welsh structures, which consist of cables strung from poles. At a cost of £250,000, two bat bridges were constructed. One of these, pictured, consists of three steel towers with cables suspended between them carrying mesh panels. The other consists of a single span of cables and mesh panels between concrete and steel anchors either side of a cutting. A third bat-crossing consisted of a raised parapet modification to a new road bridge. |
| Parton to Lillyhall | A595 | Dec 2008 | 34 m span between supporting steel structures | Dual | On embankment | £34,133 | - |
| Haydon Bridge | A69 | April 2009 | 19.5 m between support posts | Single | In cutting | £60,000 | - |
| Pwllheli and Criccieth | A497 | 2006 | Single | At Grade | A bat bridge was installed following the upgrade of the A497 to help the six species of bats in the area to cross the road. | ||
| Elveden | A11 | 2014 | Dual | Various | £350,000 | Six bat bridges. | |
| Gilwern to Abergavenny | A465 | 2007 | Dual | Embankment | Two bat bridges were constructed during road upgrade in locations where full bridges previously stood. | ||
| Groeslon | A487 | 2010 | Single | The road runs through the Glynllifon Special Area of Conservation which is home to a lesser horseshoe bat colony. | |||
| Norwich | A1270 | 2017 | Dual | £1,000,000 | Seven bat bridges on the Norwich Northern Distributor Road. |
France
The first bridge to be installed in France is on the A65 motorway between junctions for Roquefort and Caloy in the Landes department.Two additional bat bridges were completed in November 2012 near Balbigny, on the A89 motorway.
Germany
Two metal bridges were built in 2013 to protect the Mouse-eared Bat at Biberach an der Riss, Baden-Wuerttemberg. The structures cost £375,000.Criticism
The overall cost of bat bridges has been criticised in the House of Lords by Lord Marlesford.A team from the University of Leeds examined the effectiveness of bat bridges, gantries and underpasses. They found that one underpass, placed on a commuting route, was used by 96% of bats, but few bats used the other underpasses and gantries, preferring routes which put them in the path of traffic.