The oldest buses are so slow that, on the Dukhan to Doha route, they take out a fuse to make it go further. The fuse powers the a/c. Lovely in the summer, can you imagine? Also, sometimes they stand up to take the fuse out from a box to the left of the driver in the roof while they are driving!!
Apart from that they are nice guys. I have never had a problem in 3 years of regularly using Karwa.