Answer:
So, to make train travel possible, the world was divided into time zones, and times were standardized.
Step-by-step explanation:
The above sentence is the supporting detail from the passage that would be most important to include in a summary. This is because it actually gives a conclusion and a solution to the problem of same time that had caused accidents. Also, this particular sentence captures the main idea of the passage which makes it possible for it to be included in the summary.