Temporary tunnel opens at King's Cross St Pancras

A new tunnel connecting the Piccadilly line with the Victoria line at King's Cross St Pancras. What's odd about this tunnel is despite its size, it's only temporary, while they rebuild the old route as a connection to the Northern Ticket Hall.

I've drawn a quick sketch of the area. The new tunnel replaces part of the Thameslink interchange tunnel, and once King's Cross Thameslink closes in December will serve only as an interchange route between the Piccadilly and Victoria lines (which are also connected by a shorter route at their southern ends), and as a route from both lines to the Thameslink station entrance on Pentonville Road.

Update: Yes, it truly is temporary

[via]