 The Queen 's Gate Tunnel ( Welsh : Twnnel Porth y Frenhines ) , also known as the Butetown Tunnel , is underneath southern Butetown and follows a line underneath the Wales Millennium Centre . The 715 m ( 2 @,@ 346 ft ) twin tunnel was constructed using the cut and cover method of construction , which involves digging a trench for the tunnel and then roofing it over . The tunnel was constructed using reinforced concrete and a central wall separates the two sets of traffic . 
 The Queen <a href='null_genetive' title='1'><mark>'s</mark></a>Gate Tunnel ( Welsh : Twnnel Porth y Frenhines ) , also known as the Butetown Tunnel , is underneath southern Butetown and <a href='uninflect' title='2'><mark>follows</mark></a> a line underneath the Wales Millennium Centre . The 715 m ( 2 @,@ 346 ft ) twin tunnel was constructed using the cut and cover method of construction , which <a href='uninflect' title='3'><mark>involves</mark></a> digging a trench for the tunnel and then roofing it over . The tunnel was constructed using reinforced concrete and a central wall <a href='uninflect' title='4'><mark>separates</mark></a> the two sets of traffic . 
Da Queen  Gate Tunnel ( Welsh : Twnnel Porth y Frenhines ) , also known as tdaButetown Tunnel , is underneath southern Butetown and follow a line underneath the Wales Millennium Centre . The 715 m ( 2 @,@ 346 ft ) twin tunnel was constructed using thdaut and cover method of construction , which involve digging a trench fa the tunnel and then roofing it ova . The tunnel was constructed usin reinforced concrete and a central wall separate the two sets of traffic .