A <a href="https://en.wikipedia.org/wiki/Chicago_Transit_Authority" id="mw6Q" rel="mw:WikiLink" title="Chicago Transit Authority">Chicago Transit Authority</a> <a class="mw-redirect" href="https://en.wikipedia.org/wiki/Elevated_train" id="mw6g" rel="mw:WikiLink" title="Elevated train">elevated train</a> <a href="https://en.wikipedia.org/wiki/1977_Chicago_Loop_derailment" id="mw6w" rel="mw:WikiLink" title="1977 Chicago Loop derailment">rear-ends another and derails</a>, killing 11 and injuring 180, the worst accident in the agency's history.