Andy Rouse / Man playing in deep snow with dogs (two German shepherds and a spaniel) on closed road on Caerphilly Mountain, Caerphilly, South Wales, UK, December 2010, Model released

Andy Rouse / Man and woman walking with two German shepherd dogs along closed road on Caerphilly Mountain, Caerphilly, South Wales, UK, December 2010

Ernie Janes / Warning sign for road / track closed due to coastal erosion, Happisburg, Norfolk, UK

Kirkendall-Spring / Lava flow over the Chain of Craters Road, with road closed sign, in Hawai'i Volcanoes National Park. The Big Island of Hawaii, USA, December 2008

Kirkendall-Spring / Lava flow over the Chain of Craters Road, with road closed sign, Hawai'i Volcanoes National Park. The Big Island of Hawaii, USA, December 2008

Ingo Arndt / Christmas Island Red Crab (Gecarcoidea natalis) migration causes road closure, Christmas Island, Indian Ocean, Territory of Australia

Ingo Arndt / Christmas Island Red Crab (Gecarcoidea natalis) mass crossing closed road during annual migration, Christmas Island, Indian Ocean, Territory of Australia

Tom Gilks / Road closed for 'The Wave' climate change march ahead of the Copenhagen climate summit, cyclists part of the protest, London, UK, 5th December 2009

Stephen Belcher / Christmas Island Red Crab (Gecarcoidea natalis) crossing the road with sign in the background, Christmas Island, Australia

Stephen Belcher / Christmas Island Red Crab (Gecarcoidea natalis) group crossing road during annual migration, Christmas Island, Australia

Stephen Belcher / Christmas Island Red Crab (Gecarcoidea natalis) group crossing road during annual migration, Christmas Island, Australia