A majority of delegates at a conference of the center-left Social Democrat party backed a resolution stating that "a fast and unbureaucratic path to climate protection is the introduction of a general speed limit of 130 kilometers per hour," or 80 mph.
Many stretches of German autobahn have no speed limits. However, the current surge in concern over carbon dioxide emissions has put that tradition under renewed scrutiny.
Earlier this year, EU Environment Commissioner Stavros Dimas suggested introducing a speed limit, drawing a cool response from Berlin.
Saturday's decision has no binding effect on government policy, and the party's conservative coalition partners, including Chancellor Angela Merkel, have regularly rejected calls for an overall speed limit.
Leading Social Democrats - including Environment Minister Sigmar Gabriel and Transport Minister Wolfgang Tiefensee - also have questioned the logic of speed limits. Gabriel has argued that they would reduce incentives for manufacturers to produce more environment-friendly engines.
Deputy party leader Andrea Nahles said in an interview with the Welt am Sonntag newspaper that she regretted the decision, arguing that what is needed are "new technologies, new (car) fleets and alternative fuels - not new rules."