Some students (and teachers) think that it's a good idea to write a long introduction. I disagree, and I recommend that you keep the introduction short. Let's compare some examples.
My short introduction:
People have different views about how best to improve transportation in cities. While better provision for cyclists would be a positive measure, I would argue that further investment in public transport should be the priority in most cities.
A long introduction written by a student:
Nowadays, there is a large debate around the ideal transportation means that should be promoted by governments. Some believe that means like bicycles should be supported, while others feel that spending should be directed toward public transportations. I think that both means have to be subsidized because each has advantages and potential disadvantages. In this essay, I shall discuss and analyze both views.
The long introduction above is a little repetitive, but otherwise it's fine. The main problem is the extra time that you waste if you write four sentences instead of two. This is time that could be spent on the main body paragraphs, which are the key to a high score. A long introduction won't help your score at all, but longer and better main body paragraphs will.