Cyclists still travel between Gretna and Carlisle on the route
Marathon cyclists have been warned off a route at the Scotland-England border when travelling from Land's End to John O'Groats.
The A74 used to be a dual carriageway north of Carlisle but is now being converted into an extension of the M6.
Special orders have now been introduced banning cyclists and pedestrians from the route during construction work.
The Highways Agency said many people were still using the road to travel by bicycle between Gretna and Carlisle.
The £175m extension of the M6 is to plug the "Cumberland Gap", enabling drivers to travel from Glasgow to London entirely by motorway.
However, roads bosses fear people are ignoring signs warning them off the route.
Traffic officer Glenn Lamont, who helps patrol the M6 and A74 up to the Scottish border, said: "With the summer season upon us, we have noticed a large increase of cyclists using the A74 to travel between Gretna and Carlisle and vice-versa.
"There is signage for cyclists at both Junction 44 of the M6 and at Guardsmill interchange on the A74, telling them to use the A7 through Longtown.
"Some cyclists are ignoring this and with the roadworks and contra flow in place there is a really high risk of an accident involving cyclists."
He added that a lot of the cyclists were using the A74 as a link in Land's End to John O'Groats marathons.
The Traffic Officer Service has alerted local tourism offices to the danger and given information about the alternative safer route.