Well.. Its not bad design.. Being a driver you should know how high you are specially if you are truck driver. Why cant you just follow the sign?? Road signs are the key.. If you cant follow a sign then you should not be on the roads. Yes if there are no signs or alerts before the underpass, I will throw a blame on authorities as well.
I am sure there are signs every where before every under pass (Please verify and confirm abut this one) . As I said it happens everywhere. In NYC there are averaging 100 plus bridge strikes every year. This is a big number and impact traffic and revenue.
Anyways Most of underpasses within urban areas don't allow long trailers and trucks all over the world. There are multiple reasons for that. One reason is to detour commercial trucks entering your urban and main city centers via main road arteries which are traffic life lines. I am sure you read in news that traffic was horrible due to this bridge strike. It will remain horrible if you allow these trucks in city via same routes . Underpasses are designed after collecting months of data. Ground water conditions also impact the design excavation/ cut as well.
Also If some under passes are 16 and some are 11 there is a reason for that as well. Under passes are designed according to surrounding elevations. The change in height will also change the length of approach. There is always a service road or other truck routes which the trucks needs to follow. Signing, sensors and technology, enforcement and education will help to avoid such events.
Also as a knowledge base: There is a difference between overpass and underpass. 
In case of underpass, the lower road changing elevation/ slope like you have in Lahore. An overpass like you have on motorway. roadways passing over the main highways. The main highway keeps its elevation. The overpass should be minimum 16 feet high standard.
