Raw dash cam video from a witness:
If you pause the video right at the beginning, you can see that the trailer bottomed out on the tracks. The truck driver clearly knew this because he got out of the truck before the train hit. Given that the crossing arms came down on top of the truck, it had probably been there at least a couple of minutes before the train approached, so this likely isn't a trying-to-beat-the-train situation.
It happened around 4:30pm. This is the same track that Amtrak uses for all of its south-of-Richmond service including the Silvers, Palmetto, Carolinian and the Norfolk NER. It appears the track has reopened as of 10pm tonight as amtrak.com is showing the southbound 97 as only 12 minutes late.