Traffic jams can cause hours of delays. Traffic can be caused by a number of things such as accidents and breakdowns, events or roadworks and even just during normal rush hour. Being stuck in traffic jams is not fun and can cause drivers to get angry and end up doing silly manoeuvres.
You cannot always avoid traffic but you can try and find out about traffic that has already built up so you can plan to avoid particular areas when planning your route. Google Maps is one of the apps available on the Itunes store and the Android store, which offers a traffic overview showing you a colour coded system to show what the current traffic flow is like on these roads.
Some Sat Navs also have traffic information and often they will automatically re-route you to follow a quicker route if it picks up that there is traffic queuing ahead. Often these Sat Navs pick up information from the road agencies and also from other users of their Sat Nav, which feeds information back to a central database.