Zipcar App Redesigned

I'm a keen member of Zipcar in London but I've found using the app a bit tricky. So with a clean slate I decided to try redesigning the app how I'd like to use it - having bigger buttons so you could use it whilst in the car and keeping Zipcar's colour palette the same throughout.
The biggest feature is having a one-click button to add another 30 mins to your journey and having the 'call' button on each screen.

Full design here: http://www.aaronbuckley.com/portfolio/zipcar-app-redesign