The phrase "busy road" refers to a street or highway where there is a lot of traffic or many cars passing by. It means that the road is crowded with vehicles and there is a lot of movement and activity happening on it. Full definition
However, under a quarter thought that people driving on busy roads should pay more and a similar proportion said that people driving at busy times should pay more. (politics.co.uk)
You'll also end up paying more if you live in a place with a lot of busy roads. (carinsurancequote.net)
Indeed, playing fields may be used as buffer zones to separate school buildings from busy roads where necessary. (educationbusinessuk.net)