In case it's been a while since you last saw an easily avoidable crash, we've got you covered.
The driver of this semi either wasn't paying attention, which sounds unlikely when driving on a snow-covered road at night, or he completely misjudged the situation, failing to slow down on time.
As pointed out in the description, the truck was also heavy, which could have contributed to the accident, although the late braking is often the number one factor in these types of scenarios.
Right before the impact, you'll notice a gap between that stationary semi on the right and the van in the middle of the road. If the driver at fault could have somehow steered between the two vehicles, he might have managed to stop before hitting anybody.
If he had made it through, he could have used the guardrail to slow down the semi, if conventional methods continued to prove ineffective.