It is a good idea to check before you are too drunk to drive. The answer is: it depends on the route. RTD already has rail that is being extended. Most routes do not run 24/7. However, some run 24/7 in the scheldule with reduced stops and reduced frequency. The 24/7 routes are along the main busy streets such as East Colfax, Route 15, Broadway, Route 0, West Colfax, Route 16. The rail runs close to 24/7 but with some reduction in frequency.
You need to check it the website The Regional Transportation District Home Page
. All buses that I have taken are reasonably safe but very some of these middle of the night routes would require caution and vigilance, so stay sober.