A Valleys metro is possible now though with third rail electrification, and the opportunity of using surface rolling
stock that the London Underground is in the process of replacing early.
The torque is transmitted mostly by involute surface rolling
, minimising the faces sliding friction.
When they looked at the benefits that could be achieved by using processes to improve the forged steel knuckle (e.g., surface hardening; surface rolling
), the researchers concluded the processes alone wouldn't provide that great of an improvement to the part as designed and that a redesign would be necessary to make cost and weight improvements.