What is PD 6688-1-4- Background information to the National Annex to BS EN 1991‑1‑4 about?  
PD 6688-1-4 is a background paper that gives non‑contradictory complementary information for use in the UK with BS EN 1991-1-4:2005 and its UK National Annex.
PD 6688-1-4 gives:
- Background to the decisions made in the National Annexes for some of the Nationally Determined Parameters
- Commentary on some specific subclauses from BS EN 1991-1-4:2005
- additional data that can be used in conjunction with BS EN 1991-1-4:2005
Who is PD 6688-1-4- Background information to the National Annex to BS EN 1991‑1‑4 for? 
PD 6688-1-4 on background information to the National Annex to BS EN 1991‑1‑4 is useful for: 
- Documentation agencies
- Documentation specialists
Why should you use PD 6688-1-4- Background information to the National Annex to BS EN 1991‑1‑4?  
When there is a need for guidance on a subject that is not covered by the Eurocode, a country can choose to publish documents that contain non‑contradictory complementary information that supports the Eurocode. PD 6688-1-4 provides just such information and has been cited as a reference in the National Annex to BS EN 1991-1-4:2005.
PD 6688-1-4 gives non-contradictory complementary information for use in the UK with BS EN 1991-1-4:2005 and its UK National Annex. BS EN 1991-1-4 contains guidance applicable to all structures. Therefore, B/525/10, which is responsible for Eurocodes for the design of bridges, was consulted in the drafting of PD 6688-1-4.
As a guide, PD 6688-1-4 takes the form of guidance and recommendations. It should not be quoted as if it were a specification and particular care should be taken to ensure that claims of compliance are not misleading.
