Fixed speed limits are the most common kind of speed limit, usually identified by a number within a red circle on road signs entering the speed limited area. However, variable speed limits are increasingly being used on ‘smart motorways’. These motorways monitor traffic flow and can make adjustments to reduce congestion when required – for example, by operating the hard shoulder as a live traffic lane, or introducing a temporary speed limit when there’s a traffic build up, roadworks or stranded vehicle. This variable speed limit is clearly displayed on the gantries across the motorway, and is usually enforced by average speed cameras behind the signs. Bear in mind that the maximum speeding fine on a motorway is £2,500.