Google is taking its self-driving cars to a fourth city in an expansion of its ongoing development. The latest location for testing is Phoenix, Arizona, which is significantly more arid than any city previously used as a proving ground.

Speaking to Reuters, Jennifer Haroon, Google's head of business operations for the self-driving car project, noted that the desert conditions will further the company's understanding of "how our sensors and cars handle extreme temperatures and dust in the air." Modified Lexus SUVs have already begun to map the Phoenix area, checking for street layouts, lane markers, traffic signals and curb heights.