<p>The circular economy (CE) is often described as a sustainable system where socioeconomic advancement is obtained via a reduction in non-renewable resource extraction coupled with heightened material recirculation. However, the extra energy/material inputs and losses associated with numerous CE initiatives, including recycling, can negate many of the environmental gains associated with circular economy-based development. In this paper, we introduce a circularity index called the “Ecocircularity Performance Index” (ECPI) with the goal of evaluating resources in terms of both quantity and quality. The EPCI was applied to a UK car-based passenger mobility case study, where we compared the carbon emissions and material circularity for an internal combustion engine vehicle (ICEV) relative to that of a battery electric vehicle (BEV). The ECPI value ranges from 0 (zero circularity) to 1 (100% circularity) and constitutes material flow recoverability (circularity quantity) alongside environmental considerations (whereby carbon emissions were used as a proxy for circularity quality). In 2015, the average UK ICEV’s ECPI value was 0.01 while a BEV’s was 0.1. A BEV performed better because of its higher circularity quality performance over the ICEV, which matched the BEV in terms of material loop closure. The implementation of typical CE transportation strategies including vehicle fleet electrification, resource efficiency, and shared mobility would improve the ECPI value to 0.5. We consider the ECPI’s inclusion of material quality to be an important step in widening the scope regarding what is measured in circularity indexes, as solely focusing on quantities of resource flow inputs and outputs can inadvertently hinder sustainability progress.</p>