There are more than 100 10-hour spaces on the harbour arm, which was returned to public use in February, after being home to Covid testing facilities during the pandemic.
But the area has quickly attracted problems.
Harbourmaster Captain David Barker said the East Arm access would now be restricted between 9pm and 6am every day.
‘This is because of antisocial behaviour by a small number of individuals who have been driving vehicles at high speed on the East Arm during the hours of darkness, and depositing litter in the roadway,’ Captain Barker said.
St Peter Port constable Zoe Lihou said she was aware there was a long-running culture of ‘Kev’ racing among young people in Guernsey, which did present safety concerns.
‘They are often young, often inexperienced and that is when accidents happen,’ she said.
She knew some people might question blocking off the East Arm, as the racers might move somewhere else.
But she hoped this would at least make it safer.
She added that she had seen incidents of racing herself – including two scooter riders lining up and then racing along the road by the La Vallette bathing pools. This was despite the area being narrow and busy with cars and pedestrians. She was worried someone would get injured due to the racing.
There has also been another safety change at the harbour.
Several planters have been placed at the entrances to the crossing between North Beach and the Liberation Monument.
Captain Barker said the move had taken to place to encourage pedestrians to stop and check that the road is clear before crossing.
‘In addition, it is hoped that this will prevent cyclists from riding across the crossing, which is not part of the east coast cycleway,’ he said.