Starting in January 2012 the Department for Transport is conducting a trial of longer semi-trailers. The trial involves 900 semi-trailers of in length (i.e. longer than the current maximum), and a further 900 semi-trailers of in length (i.e. longer). This will result in the total maximum length of the semi-trailer truck being for trailers in length, and for trailers long. The increase in length will not result in the weight limit being exceeded and will allow some operators to approach the weight limit which may not have been previously possible due to the previous length of trailers. The trial will run for a maximum of 10 years. Providing certain requirements are fulfilled, a Special Types General Order (STGO) allows for vehicles of any size or weight to travel on UK roads. However, in practice any such vehicle has to travel by a route authorized by the Department of Transport and move under escort. The escort of abnormal loads in the UK is now predominantly carried out by private companies, but extremely large or heavy loads that require road closures must still be escorted by the police.