Two authors from the National Technical University of Athens recently published a paper on 3D road design. You can find copies of the paper online. It is called”Three dimensional road design by applying differential geometry and conventional design approach criteria” and is available from sites such as Academia and Research Gate.
The technical language of the paper is directed towards mathematicians rather than engineers, but that does not lessen its importance in the debate on road design practice. One point raised by the authors is that their proposed method “is fully automated and no user interference is required” – which might sound somewhat threatening to conventional highway design people. A second point which arises is whether conventional design standards prepared for 2D design approaches relevant to 3D design approaches – I even wonder, given that we live in a 3D world rather than a 2D world – whether conventional design standards are right at all”.