One of the four seminars at the 75th jubilee of the Danish Road Institute addresses the work of the Institute within the field of “Knowledge on big roads”. What knowledge on big roads will be necessary in some years? It is now that ongoing research and development should create the base for knowledge about the design, construction and maintenance of bigger road constructions. Report 126: “Knowledge on big roads” contains – apart from the presentations made at the seminar “Knowledge on big roads” - an additional paper on the subject. The report does not cover the entire knowledge in this big field. However, it does reflect important elements of the future work of the Danish Road Institute. The report 126 contains the following papers: Upgrading of the road network – the traffic is growing: how should we upgrade the roads, so that they have a longer lifetime? Designing of pavements: The Danish Road Standards and the American AASHTO 2002 Design Guide. Maintenance of structures – bridges are the main cross points of roads and this requires special maintenance. Long-life pavements – what have we learnt from the past and how should we construct roads in the future. Flexible stone mastic joints – how good is their lifetime?