Early on, operations became troubled by the tunnel's lack of ventilation; the combination of steam locomotives and inadequate air flow led to dangerous sulphuric acid vapour accumulating along the roof, which compelled locomotive crews to lie on the floor seeking fresher air to breath. While protective equipment was issued to the crews, the problem was not truly eliminated until the introduction of electric traction during the 1920s. During the 1970s, the interconnecting Arlberg Road Tunnel was built alongside the earlier railway tunnel, there is a minimum distance of 150 distances between the actively-trafficked bores.