The line has a speed limit of 75 mph ( 121 km\/h ) , although the Class 357 Electrostar trains are capable of 100 mph ( 160 km\/h ) .
The line currently has a maximum speed limit of 75 mph ( 121 km\/h ) , although the Class 357 Electrostar electric multiple unit trains which run on it are capable of a maximum speed of 100 mph ( 160 km\/h ) .