I think you need to write the parameters of the URL without {}, something like:

?app_id=JPRO.....iUY&app_code=PdZ.....x-og

Also, sharing your credentials here is not a very safe practice :)

I think you need to write the parameters of the URL without {}, something like:

?app_id=JPRO.....iUY&app_code=PdZ.....x-og

Also, sharing your credentials here is not a very safe practice :)

In any case, the following works loading a CartoDB basemap and overlying a Nokia transit layer:

L.tileLayer('http://{s}.basemaps.cartocdn.com/light_nolabels/{z}/{x}/{y}.png', 
    {attribution: '&copy; <a href="http://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors, &copy; <a href="http://cartodb.com/attributions">CartoDB</a>'
  }).addTo(map,0);

L.tileLayer('https://1.traffic.maps.cit.api.here.com/maptile/2.1/flowtile/newest/normal.day/{z}/{x}/{y}/256/png8?app_id=DemoAppId01082013GAL&app_code=AJKnXv84fjrb0KIHawS0Tg', 
    {}).addTo(map,1);