Here's why:
* Weather is a common noun and is not capitalized unless it's part of a proper noun (like "Hurricane Weather").
* Drive is a common noun and isn't capitalized.
* Railroad is a common noun and isn't capitalized unless it's part of a proper noun (like "Southern Pacific Railroad").
* River is a proper noun when referring to a specific river, like the Mississippi River, and therefore should be capitalized.
Let me know if you have any other capitalization questions!