I would like to express my gratitude to all those who gave me the possibility to complete this thesis. I want to thank the Department of Transport of the former Interim Government of Namibia for giving me permission to commence this thesis in the first instance, to do the necessary research work and to use departmental data. I have furthermore to thank the former Secretary for Transport, Mr C.N. Herloff-Petersen and the present Under-Secretary of Transport of the Ministry of Works, Transport and Communication of the Republic of Namibia, Mr W. Ravenscroft who gave and confirmed this permission and encouraged me to go ahead with my thesis. I am bound to the Honourable Minister Richard Kapelwa Kabajani and to Dr Peindgondjabi Titus Shipoh, Permanent Secretary in the Ministry of Works, Transport and Communication for their stimulating support.
I am deeply indebted to my supervisor Prof. Dr. S. Huschek from the Technical University Berlin-Charlottenburg whose help, stimulating suggestions and encouragement helped me in all the time of research for and writing of this thesis.
My former colleagues from the Department of Transport supported me in my research work. I want to thank them for all their help, support, interest and valuable hints. Especially I am obliged to Messrs C.L. von Solms, F.J. Poolman, K.J. Detering, E. Albrecht and G.K. Kleber. I also want to thank Mr S. Augustyn for all his assistance on the ministerial computer. My private secretary Ms K. Labuschagne was of great help in difficult times. My son, Alexander Dierks as well as Tove Dix looked closely at the final version of the thesis for English style and grammar, correcting both and offering suggestions for improvement.
Especially, I would like to give my special thanks to my wife Karen whose patient love enabled me to complete this work.