(ANSA) - BELGRADE, SEP 17 - The opening of the exploratory tunnel of the Brenner Base Tunnel (BBT), which will take place tomorrow in the presence of Prime Minister Giorgia Meloni and Austrian Chancellor Christian Stocker, is a significant step forward in the realisation of this massive cross-border project. It is also a highly symbolic moment because the Italian-Austrian border will now be crossed underground. Work began in 2007 and is expected to be completed by 2032. The tunnel will be 55 kilometres long and connect to Innsbruck's existing ring road, bringing the total length to 64 kilometres. At a depth of 12 metres beneath the main tunnels, the 6-meter-wide exploratory tunnel will provide geological information for the construction of the 8.1-meter-wide main tubes. The tunnel is 794 metres above sea level, while trains currently have to climb 1,370 metres to reach the pass. (ANSA).