Backstory: Have you ever taken an uber pool? My favorite follow-up: Have you ever taken a second uber pool? It was probably my worst experience in getting to my destination. I was one block away and the driver was re-routed to pick up another passenger who was dropped off before I finally reached my destination.
The Idea: An efficient ride sharing app.
Deep Dive: This one is quite a heavy lift but all the pieces exist. I've read stories about algorithms that make delivery companies (FedEx, UPS, DHL) more efficient. Every minute and gallon of gas matters when you're in the delivery business. Using similar technology in car pool/ride sharing services would be huge.
The value to your customers is a cheaper cost for a slightly less efficient path, compared to a solo car trip. Once you have the algorithm dialed in to pick people up and drop them off in the most efficient path, you'll win in this space (better mousetrap).
There's a possibility that with efficiency, the driver will actually make more money.
Validation: Uber pool is huge!
Monetization: Similar to Uber and Lyft you would charge a fee for the pickup and deliver payment to the driver.