The odd sentence is Option 2. It is the only sentence that discusses the improvement of public transport services due to increased ridership. All other sentences discuss a decline in the use of public transport, with reasons and contributing factors.
Thus, Option 2 disrupts the coherence of the paragraph.
Arrange into a paragraph:
1. The streets were wet.
2. We decided to cancel the picnic.
3. Dark clouds covered the sky.
4. Soon, it began to rain heavily.