I think that you should use "forecasting language" for this task because the year 2030 is the future. Moreover, I think that the overview should be the opening idea for the rest paragraph. In other words, the 2 body paragrahphs should support every idea of the overview. Below is my answer for this task: (this is just my idea, if it is not helpful, you can skip it).
"The line graph illustrates the number of people who go for work by three different traffic means in the UK over the course 40 years from 1970 to 2010, and the expectation up to 2030.
It is clear that cars were the most favorable mean and the number of people using cars significantly increase over time. Moreover, the number of commuters going to work by bus gradually decrease, while the number of transporters going to work by train dramatically rise in surveyed period.
The number of commuters using cars remained stable at about 5 millions in the first 10 years from 1970 to 1980, following by an exponential growth after 20 years, and then level off at approximately 7millions in 2010. It is estimated that this figure will dramatically increase to nearly 9millions in 2030.
The quantity of people who used bus as a mean to go for work gradually decrease from 4millions in 1970 to 3.5millions in 2010, while this period experienced a soaring rise in the number of people using trains, with 2millions in 1970 and 3millions in 2010 respectively. Consequently, it is projected that trains will overtook buses and set to be a second most used mean in 2030, with 5millions, compared to 3millions using bus."