Rail-mounted lathe - photo

[awright]

The primary purpose of turning the wheels and grinding the rails after they have been put into service is to control noise and vibration - both wayside and in the vehicle. For this purpose it doesn't matter if a wheel is a driver or not and in most 8 wheel transit vehicles, all wheels are drivers anyway.

As acoustical consultants brought in to advise the CTA (Chicago Transit Authority) on how best to spend a federal grant to control noise some 50 years ago, we advised that grinding the wheels and rails was the most effective use of the money. However, transit management is reluctant to do so because the metal removed dramatically reduces the miles of service obtained from wheels and rails. At the time, rumor had it that the CTA was proud to get a million miles per wheel.

The last time I was in Chicago (2019) the noise in CTA vehicles and underground stations was dramatically better than in the 1970s when noise was deafening in the subway stations right down to the instant entering trains stopped.

The phenomenon of rail corrugation (development of ripples in the rail surface) and pitting of wheels and rails (due to fatigue from the high contact pressure between the wheels and rails) has been studied extensively and last I heard (decades ago before I retired) no one had solved the problem.

One phenomenon Chicago struggled with back then was that rails would develop a very thin film of rust over weekends when some rails were out of service. When service started up on Mondays the rust and water would act as a lubricant between wheels and rails resulting in skids during braking with older controls less sophisticated than we have today. A single skid would cause a flat spot on the wheel - possibly a wheel that had just been ground or turned - resulting in the familiar thump - thump - thump very audible in the vehicle and at the wayside. And the thumping would pummel the rail that may have just been ground.

The benefit in reducing noise from grinding wheels and rails is dramatic. Going from unground, rough rail onto a section of ground rail is like driving a car from rough pavement onto snow.