The relation between transport’s positive effects and its negative social and environmental impacts could be compared to that of Siamese twins. Not only is it difficult to separate the twins, but doing so is a highly risky business. Separation could lead to the death of both parts. Similarly, eliminating most or all of transport’s negative impacts could represent a threat to transport as we know it. Therefore, it is difﬁcult to create a comfortable match between transport and sustainable development.