It is interesting to note that people who use the Dubai Metro to commute to work often complain that the carriages are jam packed full of passengers. Although the frequency of trains has been increased in recent months it would be interesting to know if the RTA has any plans for increasing the capacity of the trains of the frequency of them in peak hours.
In particular, on car free day, the trains were packed and possibly not equipped for that kind of usage on a regular basis. It seems unlikely that it is possible to increase the capacity of the trains unless the station platforms have been designed to accept trains with more carriages.
However, it does look possible that the frequency of trains can be increased from the current level. How often do the Dubai Metro trains run I hear you ask? Well in the rush hour the trains run approximately every 4 minutes with bigger gaps (8 minutes) out of rush hour. So, there is scope to increase more trains although this will inevitably put a greater strain on the system and will also involve the cost of buying new trains.