Smart cities technologies are gradually changing our urban landscape thanks to the proliferation of billions of smart devices permanently connected through the internet. Among technologies with the highest impact on citizen's quality of life are intelligent transportation systems and in particular, smart parking applications. In this paper, we present a study evaluation the design of a smart parking assistant developed in our lab. The system is implemented as a mobile app with an integrated GUI adapted for Android tablets. The app extends common park guidance information systems (PGI) offering suggestions based on parking fee or proximity to the destination. Two novel features -beyond the state of the art of currently available systems -are added: the use of natural language and the ability to react in real-time to changes in parking occupancy. If the number of parking lots drops to a critical level, the application redirects the driver to another parking place. Furthermore, the app includes GPS and Google maps interfacing modules which enable the application to detect the driver location and calculate the nearest car park distance. A group of five experts with a background in interface design and natural language processing evaluated the prototype using Nielsen's set of heuristics in a think-loud approach. Results and implications for further interaction design are extensively discussed.

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