TCS works by the application of braking action on the wheel that is spinning faster than the the other. When testing that on pure ice, I imagine that it can be demonstrated to be useful for novice drivers. Roads, however, are seldom pure ice.
In slush highway conditions the TCS system will apply the braking action to the wheel that's spinning in slush. That side of the vehicle is already being slowed down by the drag created by slush and the car is starting to swerve to the slush side. Then TCS kicks in and you have a head-on or rollover crash.
I experienced that on my first vehicle equipped with TCS. I am a good driver. I was perplexed about why my van was always wanting to go left or right. Control was virtually impossible. Then my brain kicked in about the TCS. I turned it off, and presto - I was a good safe driver.
I have had hundreds of opportunities to experience that since then. Not only does TCS take you off course, it also hides the slipperiness of the road from the driver, by preventing slippage while accelerating in black ice road condition. Then when it's time to stop, you can't stop on time because the road is slipperier than you thought.
In deep snow on city streets at speeds below 30 km/h TCS may occasionally be useful.
I need to buy a new VW soon and I really need to be able to buy a car where that feature can be turned off, or better yet, a car without TCS.
The following is from Wikipedia:
A traction control system (TCS), also known as anti-slip regulation (ASR), is typically (but not necessarily) a secondary function of the anti-lock braking system (ABS) on production motor vehicles, designed to prevent loss of traction of driven road wheels. When invoked it therefore enhances driver control as throttle input applied is mis-matched to road surface conditions (due to varying factors) being unable to manage applied torque.
Intervention consists of one or more of the following:
- Reduces or suppress spark sequence to one or more cylinders
- Reduce fuel supply to one or more cylinders
- Brake force applied at one or more wheels
- Close the throttle, if the vehicle is fitted with drive by wire throttle
- In turbo-charged vehicles, a boost control solenoid can be actuated to reduce boost and therefore engine power.
Typically, traction control systems share the electro-hydraulic brake actuator (but does not use the conventional master cylinder and servo), and wheel speed sensors with the anti-lock braking system. The spinning wheel is slowed down with short applications of brakes, diverting more torque to the non-spinning wheel.