An accident on the Isle of Man's Mountain Road led to a delayed and shortened Festival of Motorcycling practice session on Wednesday.
It has led organisers to add two afternoon sessions to the programme after Monday and Tuesday's practices were cancelled due to poor weather.
Clerk of the course Gary Thompson said the problems were "very frustrating".
He added that the extra sessions are needed to ensure riders gain sufficient practice ahead of racing.
Organisers said roads will be closed around the TT Course between 12:30 BST and 16:00 for the afternoon session and 18:00 and 21:00 for the evening.
So far, competitors have only completed one full session ahead of the first scheduled race on Saturday - with TT star Dean Harrison setting the pace.
The two-week event, held on the Isle of Man TT course, incorporates both the Manx Grand Prix and Classic TT races.
The Isle of Man Marshals Association has meanwhile said it is in "desperate need of marshals".
More than 500 marshals are required for each session on the 37.75-mile course before the clerk will give it the go ahead.