Shuttles are a safe and rapid transportation method for colonists between distant Domes and can also deliver resources reliably wherever needed - distance being irrelevant. When not in use, they are stationed at Shuttle Hubs, where they are maintained and refueled.
Background
Shuttles are optimized to traverse the low-density and low-pressure atmosphere of Mars. Their groundbreaking drives can take off vertically from anywhere, without the need of a runway or landing platform of any sort.