1. Abeli , W.S. 1985.Forest road planning and control by mathematical programming and time study analysis, 229Morogoro: Sokoine University of Agriculture. Unpub. PhD thesis
2. Planning the Construction of Forest Roads by Linear Programming
3. Caterpillar. 1982.Caterpillar performance handbook, Edition 13, 544Illinois, USA: Caterpillar Tractor Co. Peoria.