headway [hedweɪ]
progress or rate of progress (in achieving sth);
the average time interval between consecutive vehicles (e.g. trains, buses, etc.) on a regular service travelling in the same direction on the same route;
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http://www.oxforddictionaries.com/
http://dictionary.cambridge.org/
http://www.wordreference.com/
http://www.merriam-webster.com/
metaphraze 