Many countries publish “standards“, notes, advice and requirements related to the geometric design of roads. But as I have argued before (see for example here) there are too many of these standards. What makes life more difficult for engineers is that most of these standards suffer from one or more of the following problems:
A standard may suggest values for a parameter such as “side friction” – but does not say where the values come from. For all the reader may know, they may be based on research made in another country almost a century earlier. The reader should be able to trace back the suggested values to their original source.
The information presented may be incomplete. To take “side friction” as an example again, perhaps the standard only gives values for one vehicle type, or the accompanying notes forget to mention that correction factors were applied to observed values.
The standard may not define the terms which it uses. For example, perhaps the values suggested for side friction refer to wet , surfaced roads, and are “maximum side friction factors accepted for design purposes” (or desirable maximum, or whatever).
Occasionally a standard may give different values for the same parameter, either internally or where the standard is part of a series of documents.
Sometimes, suggested values are hidden in a dense jungle of explanatory notes, or spread through different sections of the same document; or the document may not have a table of contents. This makes it difficult to find values you are interested in.
Many of the parameters involved in road geometric design can be associated with different design approaches, theories and concepts. Some of these approaches and concepts may be out of date, or doubtful, or perhaps not yet widely accepted.