With most of the line rated for operation, the ECML was the fastest main line in the UK until the opening of High Speed 1. The high speeds are possible because much of the line is on fairly straight track on the flatter, eastern side of England, through Lincolnshire and Cambridgeshire, though there are significant speed restrictions because of the line's curvature particularly north of Darlington and between Doncaster and Leeds. By contrast, the West Coast Main Line crosses the Trent Valley and the mountains of Cumbria, with more curvature and a lower speed limit of . Speeds on the West Coast Main Line (WCML) were increased with the introduction of tilting Pendolino trains and now match the 125 mph speeds on the ECML.
