Correction to: Energy-saving operation approaches for urban rail transit systems

The article “Energy-saving operation approaches for urban rail transit systems”, written by Ziyou GAO, Lixing YANG, was originally published electronically on the publisher’s internet portal (currently SpringerLink) on 27 April 2019 without open access. The copyright of the article changed on 30 June 2019 to © The Author(s) 2019 and the article is forthwith distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, duplication, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.