Huge volume of litter where Highways are working

There is a huge volume of litter on the slip roads and motorway reservation areas leading into Manchester City Centre. What is shocking is that there is a project ongoing at present to trim all the vegetation in these locations and this is being removed, but the litter has just been left there. Is it not prudent whilst you have the motorways closed that the littler is picked up also? Volunteers cannot pick litter in these locations - which I 'm sure they would if they could - so is not the responsibility of Highways to clear this litter?