Do we have any published recorded evidence of the accidents on the islands roads ? Uncommonly on the island we have 2 distinct situations that should be analysed separately but the results also looked in comparison to highlight the changes in road usage. In most counties road layouts and speed limits stay the same throughout the year but we have our normal situation with a range on limited and unrestricted speed roads and a period where one of our main roads is made one-way similar to an open road race track and increased speed limits on the remainder of the roads.
From anecdotal reports the number of accidents increases dramatically during the one way period on the mountain road so the biggest safety effect would be to enforce a 50 mph limit on the mountain during TT to stop the racing and people riding/driving beyond their abilities. It might mean that the road remains open for more than a few minutes at a time.
For the remainder of the roads unless a specific accident black spot is identified I would leave the limits but enforce in built up areas as I find the biggest issue some cars driving at 40-45 on open roads but maintaining this speed at they enter towns and villages.