If you need an open track in Cardiff; Cardiff International Sports Campus is marked as open to the public.
Running in a new city in the winter time can be tricky. Bad weather and darkness makes it hard to find good places to run.
For hardcore track runners who wants to workout on an indoor track; try National Indoor Athletics Centre.
Llandaff Fields has lighting.
Cardiff parkrun is a popular place to run in this area.
The course of Cosmeston Lakes parkrun has a soft surface for those who like to avoid the asphalt and concrete.