17 motorists have been fined for driving down Rue à L'Or.
The narrow, winding street was closed to most vehicles in 2020 to make it safer for pedestrians and cyclists.
But Guernsey Police say they received reports online that drivers had been using it as a shortcut while the top of Le Vauquiedor is shut for roadworks.
They say Rue à L'Or is not an approved diversion - and anyone caught using it inappropriately can expect to be fined:
"When Rue à L'Or was initially made a prohibited street, some leeway was given for drivers by Roads Policing Officers as people may have been unaware of the new measures.
It has now been two years, however, and drivers should simply not be using the road as a shortcut off Le Vauquiedor.
Officers took appropriate action in issuing fixed penalty notices and will continue to monitor the road going forwards, with a focus on ensuring the safety of its users."

Channel Islander abandons Bordeaux as the flames 'arrive at the city's gates'
Annual Guernsey Scarecrow Festival set to raise thousands for charity
Channel Islands face 'physical' Poland test
Baby born on Guernsey's Marine Ambulance
New interim leader for Guernsey's healthcare system
Guernsey's reservoir levels falling after prolonged dry spell
Guernsey's Commonwealth flag carrier in early Games win
Abundant year for jellyfish in Guernsey waters