Concept:
The preposition into is used when something moves from one place to another and enters a space or area.
Step 1: Understand the sentence.
The sentence describes a moving vehicle that collided with a divider and then moved into a lower area such as a ditch, pit, or roadside space.
Step 2: Evaluate the options.
• on = on top of something
• into = movement towards the inside of something
• inside = generally used as an adverb or adjective
• under = beneath
Step 3: Choose the most suitable preposition.
The natural expression is:
fell into
Therefore,
\[
{\text{Option (B)}}
\]