In reply to wivanov:
OK. Although I personally use DRT and do not switch to TRT mid pitch here is where I saw it:
http://www.summitpost.org/phpBB3/school-me-on-twin-vs-double-ropes-t60874-1...
"you had a question on your Mammut rope Phoenix 8mm and whether it can be used in twin and half rope technique in one single pitch. This is the case, you can always clip the two rope strands as twins, then split them as doubles, join again etc. This is exactly the advantage of half ropes compared to twin ropes where you always need to clip both ropes.
Hope this helps you,
best regards from Switzerland,
<named removed>
Productmanager Climbing Equipment
Mammut Sports Group AG, Birren 5, CH-5703 Seon"