The 6th International Conference on Road and Rail Infrastructure – CETRA 2020* was organized by the University of Zagreb - Faculty of Civil Engineering, Department of Transportation Engineering. The Conference was held in Zagreb, capital of Croatia. Zagreb’s history dates back to Roman times when the urban settlement of Andautonia existed at the location of the modern-day Ščitarjevo. In 1945, Zagreb was declared the capital of Croatia and today it is the cultural, scientific, economic, political and administrative centre of the Republic of Croatia, and a home to the Croatian Parliament, Government and President. It is located on the southern foothills of Medvednica Mountain and spreads along the banks of the Sava River. Culturally, it is a European city well worth visiting, with its numerous historical monuments, parks and medieval architecture. Everything is accessible by foot - from your hotel to the theatre, and for wandering around the old Upper Town or through the bustling streets of the more modern Lower Town, which has not lost an ounce of its charm despite the eternal march of time. The streets and monuments of Zagreb proudly testify to its hundreds of years of history. The 1st International Conference on Road and Rail Infrastructure – CETRA 2010 was held on 17-18 May 2010 in Opatija. The 2nd International Conference on Road and Rail Infrastructure – CETRA 2012 was held on 7-9 May 2012 in Dubrovnik. The 3rd International Conference on Road and Rail Infrastructure – CETRA 2014 was held on 28-30 April 2014 in Split. The 4th International Conference on Road and Rail Infrastructure – CETRA 2016 was held on 23-25 May 2016 in Šibenik. The 5th International Conference on Road and Rail Infrastructure – CETRA 2018 was held on 17-19 May 2018 in Zadar. Great interest of participants in topics from the field of road and rail infrastructure, as expressed during previous CETRA conferences, confirms the adequacy of the Department for Transportation Engineering’s decision to keep organising this international event. Positive comments given by participants in past conferences motivated the Department for Transportation Engineering of the Faculty of Civil Engineering at the University of Zagreb, to organise a new CETRA conference (CETRA 2020) on 20-21 May 2020 in Pula. However, due to the circumstances arising from the ongoing spread of COVID-19 - the continuing danger it still poses to public health and safety, together with an increase in travel restrictions - CETRA 2020 Organizing Committee has decided to further postpone the Conference. We held on for as long as we could, wishing that things would return to some semblance of normality. We were very optimistic, hoping that the situation with COVID-19 will be much better in October, trying our best to organize CETRA 2020 and to bring our professional and scientific community together one more time. However, the safety of the participants is our priority, and we decided it would be prudent to postpone the CETRA 2020 Conference to the spring of 2021. At the same time, postponing the Conference to the following year provided the members of our Committees valuable time to completely dedicate themselves to the determination of damage caused by the disastrous earthquake that hit Zagreb in March last year. Although we wished to organise the conference in 2020, even in the autumn of that year, we had to postpone the conference so as to be held in May 2021 on the same dates on which it was supposed to take place in 2020. We also partly kept the identity of the conference so that in 2021 the conference will be organized under the name of CETRA 2020*. The CETRA conference has established itself as a venue where scientific and professional information from the field of road and rail infrastructure is exchanged. The idea on linking research organisations with economic sector has been the guiding concept for the realisation of this conference. Conferences of this kind are undoubtedly a proper place for establishing closer ties between the economy and university operators, and for facilitating communication and inspiring greater confidence, which might result in cooperation on new projects, especially those that contribute to greater competition. Lectures organized in the scope of the conference are based on interesting technical solutions and new knowledge from the field of transport infrastructure as gained on the projects already realised, projects currently at the planning stage, and those that are now being realized, in all parts of the world. In addition to presentations given by authors from the academic community, lectures are also presented by authors from engineering practice, the idea being to ensure the best possible synergy between the theory and practice. Because of great interest for the themes relating to the field of road and rail infrastructure, as shown during the past fourth conferences (CETRA 2010, CETRA 2012, CETRA 2014, CETRA 2016 and CETRA 2018), the Department for Transportation Engineering of the Faculty of Civil Engineering – Zagreb has assumed the responsibility to organise the new CETRA Conference in 2020 as well but, as already mentioned, the COVID-19 pandemic is the reason why the conference has been rescheduled for 2021 (but keeping the identity in the form of the name CETRA 2020*). However, due to the pandemic, the form in which the conference will be organised was also changed so that it will be held via an on-line platform. This year, the 6th International Conference on Road and Rail Infrastructure – CETRA 2020* is organized with the intention of bringing together scientists and experts in the fields of road and railway engineering, so that they can present the results of their research, their findings and innovations, and analyse problems encountered in everyday engineering practice and, finally, offer solutions that will undoubtedly contribute to a more efficient planning, design, construction, and maintenance of transport infrastructure. The CETRA 2020* Conference serves as a platform for presenting a broad blend of scientific and technical papers in the fields of civil, transport, geotechnical, environmental, traffic and electrical engineering, with practical application in the road and rail infrastructure. Papers considered for publication are original papers that adequately contribute to the theory or practice of infrastructure engineering, and present either state-ofthe- art work on topics related to infrastructure, or case studies in which theory is applied to solve significant infrastructure problems. This year’s CETRA Conference attracted a large number of papers and presentations from 32 countries. More than 140 papers were presented at the Conference and are contained in these proceedings Road and Rail Infrastructure VI. We believe that these CETRA 2020* proceedings will prove to be, just like the preceding five proceedings from the CETRA cycle, highly interesting and useful to all experts exhibiting a scientific and professional interest in road and rail infrastructure. The organizers of the Conference express their thanks to all Businesses and Institutions that provided support to this Conference. Special thanks are extended to the IRF - International Road Federation, and FEHRL – the Forum of European National Highway Research Laboratories, for their assistance and support in organizing very important conference sessions relating to innovations in roads maintenance and innovative transport infrastructure development. These operators have contributed, each in its own way, to the success of this conference. Great thanks are also extended to the following institutions that have supported the CETRA conference over the past ten years: University of Zagreb, Ministry of Sea, Transport, and Infrastructure, Ministry of Science and Education, and Croatian Academy of Engineering. The Editor commends all authors for excellent papers contributed to these proceedings and wishes to thank members of the Organizing Committee and International Academic Scientific Committee, and numerous experts who participated in the review process. The gratitude is also extended to all participants for taking part in the CETRA 2020* Conference. The quality of the papers presented and the CETRA Conference is best demonstrated by the fact that a considerable interest is being expressed for most of these papers by researchers and industry operators from all parts of the world. This is not only due to the high visibility of the conference thanks to its presence in relevant databases, but is also a logical consequence of the quality of papers published in the scope of this conference series. Lectures that are organised at the conference are based on interesting technical solutions and latest findings in the field of transport infrastructure from the projects already realised, those that are at the design stage, or projects that are currently being realised in all parts of the world. In addition to representatives from the academic community, conference lectures are also given by industry operators, which constitutes the best possibly synergy of theoretical and practical achievements. Problems encountered in everyday engineering practice are analysed through papers presented at the conference, where practical solutions are offered in order to enable a more efficient planing, design, construction, and maintenance of transport infrastructure. The organization of the CETRA 2020* Conference has proven to be a greater challenge compared to the organisation of the first CETRA 2010 Conference. The persistence of organisers and great perseverance of the authors who have accepted that their valuable scientific achievements and interesting professional projects are published not in 2020 but in 2021, i.e. in the year to which the conference has been rescheduled, are the proof that only by acting together we will be able to overcome challenges that inevitably occur in the society. High quality papers published in the Conference Proceedings are the result of great efforts of the authors and reviewers as they have worked in close synergy to achieve outstanding papers included in the proceedings and presented at the conference. All those who took part in the preparation of the proceedings (authors, reviewers, members of the Organizing Committee, technical editor, and the editor-in-chief) have worked hard to enable timely publication of the proceedings. We believe that the papers published in the proceedings will be interesting not only to our colleagues in the everyday engineering practice but also to students of technical faculties where disciplines from the field of road and rail infrastructure are studied.