Ruchika. I have been involved in achieving matters since the mid 1980s, and that has included issues related to the detection of fatigue. As far as I am aware steering wheel deviation is a poor input in relation to fatigue measurement. In fact the much better measure is related to how well the vehicle maintains its position within the driving lane. If the truck wanders significantly within the driving lane including outside of the driving rain that may be the result of fatigue (though it also could be the result of a driver trying to do something within the cabin with the taking their eyes off the road ahead - for example trying to pick something up of the floor or getting something out of a glove box et cetera.
The best measure as far as I'm aware relates to monitoring the pattern of blinks by the driver.
I agree with Mr. John Lambert that monitoring eye movement of driver may be a better indicator than steering angle.
As far as your question is concerned, you may check https://www.its-rde.net/. Though it do not have explicit fatigue indicators, you may find some surrogates. Another more relevant source is https://insight.shrp2nds.us/, but this data is not freely available and you will have to purchase what you need.
The RDE dataset is very huge, so you may take a look at some of our recent papers (conducted under US NSF grant) to get an idea of specific data elements in BSMs. The second paper is not yet online but you can find a copy of it on my profile.
1. Liu, J. & A. Khattak. Delivering Improved Alerts, Warnings, and Control Assistance Using Basic Safety Messages Transmitted between Connected Vehicles. Transportation Research Part C: Emerging Technologies, 2016, 68, 83-100. DOI: 10.1016/j.trc.2016.03.009
2. M Kamrani, B Wali, AJ Khattak. Can Data Generated by Connected Vehicles Enhance Safety? Proactive Approach to Intersection Safety Management
Accepted in Transportation Research Record: Journal of Transportation Research Board.
Other fatigue/real-time driving behavior specific papers conducted under the same grant are in second-stage review and I will be happy to share if accepted.