// Define tile layers
var MapQuestOpen_OSM = L.tileLayer('http://otile{s}.mqcdn.com/tiles/1.0.0/map/{z}/{x}/{y}.jpeg', {
      attribution: 'Tiles Courtesy of <a href="http://www.mapquest.com/">MapQuest</a> &mdash; Map data &copy; <a href="http://www.openstreetmap.org/copyright">OpenStreetMap</a>',
      subdomains: '1234'
    }),
    Mapnik_BW = L.tileLayer('http://{s}.www.toolserver.org/tiles/bw-mapnik/{z}/{x}/{y}.png', {
      attribution: '<a href="https://openstreetmap.org/">&copy OpenStreetMap contributors, CC-BY-SA</a>',
      subdomains: '1234'
    }),
    stravaHM = L.tileLayer('https://d2z9m7k9h4f0yp.cloudfront.net/tiles/cycling/color5/{z}/{x}/{y}.png', {
      minZoom: 3,
      maxZoom: 17,
      opacity: 0.8,
      attribution: '<a href=http://labs.strava.com/heatmap/>http://labs.strava.com/heatmap/</a>'
    }),
    infrastructure = L.tileLayer.wms("https://bikemaps.org/WMS", {
      layers: 'bikemaps_infrastructure',
      format: 'image/png',
      transparent: true,
      version: '1.3.0'
    });

// Define tile layers
var MapQuestOpen_OSM = L.tileLayer('http://otile{s}.mqcdn.com/tiles/1.0.0/map/{z}/{x}/{y}.jpeg', {
      attribution: 'Tiles Courtesy of <a href="http://www.mapquest.com/">MapQuest</a> &mdash; Map data &copy; <a href="http://www.openstreetmap.org/copyright">OpenStreetMap</a>',
      subdomains: '1234'
    }),
    Mapnik_BW = L.tileLayer('http://{s}.www.toolserver.org/tiles/bw-mapnik/{z}/{x}/{y}.png', {
      attribution: '<a href="https://openstreetmap.org/">&copy OpenStreetMap contributors, CC-BY-SA</a>',
      subdomains: '1234'
    }),
    // stravaHM = L.tileLayer('https://d2z9m7k9h4f0yp.cloudfront.net/tiles/cycling/color5/{z}/{x}/{y}.png', {
    stravaHM = L.tileLayer('http://globalheat.strava.com/tiles/cycling/color5/{z}/{x}/{y}.png', {
      minZoom: 3,
      maxZoom: 17,
      opacity: 0.8,
      attribution: '<a href=http://labs.strava.com/heatmap/>http://labs.strava.com/heatmap/</a>'
    }),
    infrastructure = L.tileLayer.wms("https://bikemaps.org/WMS", {
      layers: 'bikemaps_infrastructure',
      format: 'image/png',
      transparent: true,
      version: '1.3.0'
    });

Change strava url to more readable and better working (?) location. Old url doesn't seem to work on mobile browsers very well.
Change strava url to more readable and better working (?) location.
Old url doesn't seem to work on mobile browsers very well.
