Nearly 30% of all traffic collisions on the M25 happen in wet weather. And in episode five, an unexpected thunderstorm has hit the region, dropping two weeks' worth of rain in just three hours. The huge amount of water has caused a flood at junction 21 covering one entire carriageway and Highways England are forced to shut the motorway. Fortunately, traffic officers Keith and Andy and team manager Kevin are on hand to deal with the situation.It's not only bad weather, which can cause problems on the motorway. Another unexpected problem is animals. They might look cute from the road when they are on the right side of the barrier, but when they're on the motorway they can cause mayhem.The M25 lies on the edge of London's green belt and with so much wildlife nearby, traffic officers need to know how to handle them. So today, Simon, Kevin and Andy are sent off for horse handling training, and they are not exactly filled with excitement about the prospect. But it's not long until Simon has to put his training into action when a horsebox breaks down in the middle of the motorway.