Residents fear a youngster could be killed if swift action is not taken to protect pupils leaving the village secondary school at home time.
They are pressing for a promised pedestrian crossing in Northwood Road, outside Harefield Academy, to be installed quickly, following an accident last Tuesday when a teenager was badly injured.
Rachel Haughan, 13, of Ash Grove broke her leg and collar bone after she was knocked over in Northwood Road at turning-out time. She will be in a wheelchair for six weeks.
Her mother Amanda Bashford, aunt Tracy Bashford and cousin Samantha Bashford, 12, who also goes to the academy, were pictured with Rachel on Monday as they campaigned for safety measures to be taken - fast.
However, Lynn Gadd, principal of Harefield Academy said: "A crossing alone, for which money has been set aside in our building budget, is not the whole solution.
"The council needs to address the fact there are no signs to warn drivers that young people will be crossing the road; nothing to show they are coming up to a school, and no flashing signs to signify speeding. We have no money in our budget for these."
Tracy Bashford said: "It is such a busy main road and you know what teenagers are like, chatting and not looking where they are going. The traffic comes down Northwood Road so fast, but if a driver sees a crossing ahead, they will usually make a deliberate move to slow down.
"This was a moped that hit her which was not going fast, but what if it had been a car or a bus? Police said when they heard there was an accident in that spot they were expecting it to be fatal.
Janet Rangeley, Hillingdon Council's head of transportation and spatial development, said: "As part of the planning application for Harefield Academy which was granted in 2005, planning obligations required the academy to install a pedestrian crossing outside the school."
Police investigated the accident but will not be taking any action. Anyone with road safety issues around the academy should email: firstname.lastname@example.org or call the council's customer contact centre on 01895 556 000.