Which characteristic describes a Personal Motorized Mobility Device?

A Personal Motorized Mobility Device is specifically characterized by having two non-tandem wheels. This feature is crucial because it defines the structure of the device, differentiating it from other vehicles that may have a different number of wheels or configuration. The design with two non-tandem wheels allows for better maneuverability and is tailored for personal transportation needs.

The other characteristics mentioned in the other options, such as the device having to exceed 48 inches in width, having an engine over 300 cubic centimeters, or the capability of exceeding 30 miles per hour, do not align with the typical definitions and regulations surrounding Personal Motorized Mobility Devices. These criteria would typically apply to larger vehicles or different categories of transportation, making them irrelevant to the definition of a Personal Motorized Mobility Device.