It's been more than a year since my tier 1 (I nicked a stationary while backing 1 mph, there was minor cosmetic damage), but thanks for your concern. I should add, after I got the warning letter my center manager told the steward there was no more discipline but he wanted to have a private word with me.
During the meeting I referenced several times working 6 days and nearly 60 hours for 14 straight weeks. I admitted to having a lapse in judgment and making a mistake, and added, this is a demanding job, not only physically but in terms of attention as well ... and unfortunately I'm a human being who gets fatigued without proper rest. All of which the company knows from its own reams of data. I told him, I'm sure I'm wasting my breath but I'd like the company to also take its fair share of responsibility for working drivers 6 days a week for long stretches despite knowing this hikes their chances of accidents and injuries.
And guess what? The boss did admit to me that it was wrong for the company to be working us 6 days, and said he strongly sympathized with my point, but unfortunately his hands were tied (no doubt this was also true, we know center managers are low-level bureaucrats these days).