Translation:I cannot go to work because of the traffic jam.
One of the many problems with the software in this language is the incomplete lists of alternative answers, where, among the missing answers, there are usually better alternatives than the poor ones offered. It does not help the previously good name of the product. For example, the answer "Because of the traffic jam, I cannot go to work" was rejected, even though it has the obligatory comma that the preferred answer lacks. As for the position of the subordinate clause in English, that may or may not be a matter of choice.
Because 'start work' in English suggests you're already in the office and just need to begin doing something. A traffic jam can't stop you at that point :) The English should be 'get to work', since it is the process of reaching the office which is a problem. ('I can't go to work' seems to suggest I haven't yet left the house, perhaps because I'm sick.)
上班 means to be in the process of working. 班, as I understand means to be on a work shift. 上 has one interpretation like being on a train going somewhere which is why they say 上火车. I think my comment is still relevant. I don't think it is being used correctly to say that you are 'going' to work.
You think it is not correct to use it as "going to work" but in the translation in the link you provided it states: to go to work / to be on duty / to start work / to go to the office. Moreover, what I was told by my teacher 上班 means generally go to work, and 下班 is pretty much get off work. In both cases it may be both being on the way to/from work as well as starting/ending work. In this context it's pretty obvious that you cannot get to work/office because of the traffic jam.