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Walter Kahlenborn, Christine Moser, Joep Frijdal, Michael Essig: Strategic Use of Public Procurement in Europe. Final Report to the European Commission, 2011
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Leendert van Bergeijk and Joep Frijdal: Steppin, Standards in Procurement and Innovation. 3rd International Public Procurement Conference Proceedings, 2008.
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Paul van der Kroon, Victor Avontuur, Joep Frijdal: Procurement of ITS, Report to Conference of European Directors of Roads (CEDR) 2008
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J.C.C. de Ruiter, W.J.J.P. Schouten, J.H. Frijdal: Automation of Travel Times Calculation in the Netherlands. 11th International Conference on Road Transport Information and Control procedings, 2002