After years of delays, the Medford Branch of the Green Line Extension opened on Monday, and it was a party atmosphere on some of the trains as passengers celebrated the new service. Subscribe to WCVB on YouTube now for more: http://bit.ly/1e8lAMZ Get more Boston news: http://www.wcvb.com Like us: https://www.facebook.com/wcvb5 Follow us: https://twitter.com/WCVB Instagram: https://www.instagram.com/wcvb5/