user: Question: What Tunnel has an Imperial Length of 307 yd?
Columns: ['County', 'Tunnel', 'Type', 'Length (Imperial)', 'Date of opening']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Londonderry', 'Castlerock', 'Rail', '668 yd', '1845 - 1853']
SQL:

assistant: SELECT "Tunnel" FROM "Table" WHERE "Length (Imperial)" = '307 yd';