How do improvements in transportation affect trade?

They make it quicker and cheaper

Explanation:

The improvements in the transportation always have a positive effect on the trade. The reason for this is that the new improvements manage to make the transportation quicker, so the trade goods can reach their destination sooner. Also, as the transportation means are becoming more advanced, they are able to cover more distance for smaller expense, and they are also bigger, so more goods can be placed on them, and that leads to a cheaper transport, thus higher profit.