The phrase "busy motorway" refers to a highway or road that has a lot of traffic, with many cars and vehicles moving quickly and closely together. Full definition
According to the BBC, president Edmund King said: «We all want to promote fuel efficiency and reduce congestion but we are not yet convinced that lorry platooning on UK motorways is the way to go about it... We have some of the busiest motorways in Europe with many more exits and entries. (businessinsider.com)
The study findings also suggest that we should avoid multi-tasking when we are reading or listening to an important message: «For example, talking to someone on the phone while driving on a busy motorway or in town, or doing some homework while listening to the newsmight lead to more shallow processing,» said Professor Leuthold. (politics.co.uk)
Perhaps most impressive is the 63's dual personality; find yourself on a busy motorway and the GLC will settle into a hushed cruise. (evo.co.uk)