Jeff Vanuga / Traffic jam caused by Grizzly bear (Ursus arctos horribilis) mother and cubs crossing road, watched by tourists and photographers, Yellowstone National Park, Wyoming, USA, October 2015.

Jeff Vanuga / Grizzly bear (Ursus arctos horribilis) crossing road, causing traffic jam. Tourists observing in background. Yellowstone National Park, Wyoming, USA. October 2015.

Jeff Vanuga / Grizzly bear (Ursus arctos horribilis) crossing road, causing traffic jam. Tourists photographing and observing in background. Yellowstone National Park, Wyoming, USA. October 2015.

Pat Tuson / Traffic jam with London red double-decker buses, Oxford Circus, Oxford Street, London, England, UK, April 2009.

Jean E. Roche / Aerial view of traffic queueing on road to reach / leave the Espiguette beach in summer, Aigues-Mortes, Camargue, Southern France, August 2008

Ernie Janes / Traffic on the M25 at night, the outer ring road Motorway around London, Herfordshire, UK

Angelo Gandolfi / An ordinary day of traffic and parking congestion problems, Naples, Italy. December 2009

Chris Gomersall / Buses, cars and taxis in traffic jam, Central London, UK.

Robin Chittenden / Traffic jam with line of cars, Newbury, Berkshire, UK May 1998

Benjamin Olson / American Bison (Bison bison) herd along road causing traffic jam, Theodore Roosevelt National Park, North Dakota