(26 Apr 2016, 6:30 pm)NK53 TKT wrote Is there a separate tunnel then just the main tunnel appears to have a 4m height limit and the smallest GNE decker (an olympian) is 4.33m
The inside lane has a 5.1m maximum headway - it's just the outside lane that has a 4.0m headway. Double deckers therefore have to use the inside lane (which service 9 usually does anyway).