From the Rule Book Module SP, HST is: class 91 locomotive with mark 4 vehicles and DVT/168/170/171/175/180/220/221/222/253/254/373/390
From the Rule Book Module SP, HST is: class 91 locomotive with mark 4 vehicles and DVT/168/170/171/175/180/220/221/222/253/254/373/390
Is it because of axle loadings?
Must have a look for the sign. The onyl one I know of is the 90 one the Totton side of the overbridge, on the Up.