Primrose Hill Tunnel near London, on the London and Birmingham Railway, opened in 1838. Engineer Robert Stephenson (1803-1859) Built through difficult London clay, the 3/4 mile tunnel cost ?240,000. The portal cost ?7,000. Picture shows elementary signally by bells, policeman with flag, and early rotating disc on a standard. From The British Gazeteer (London, 1852). Engraving.