Final answer:
Moscow's dense network of metro lines is an aspect of Soviet urban planning that contributes to sustainability goals today by promoting efficient mass transit.
Step-by-step explanation:
An aspect of Soviet urban planning that grew out of socialist ideologies yet helps achieve the goals of urban sustainability today is Moscow's extraordinarily dense network of metro (subway) lines. This network falls under the concepts of Transit-Oriented Development and New Urbanism, which advocate for robust combinations of business and residential amenities centered around efficient mass transit systems. Moscow's metro system promotes sustainable transportation by reducing traffic congestion and the urban carbon footprint, aligning with the transitional economies of contemporary urban planning.