Multi-linear Repair and Maintenance Cost Models for Tractors in Saudi Arabia

The relationship between the cumulative costs for repair, maintenance, the annual operating hours, tractor power and price, tractor age (years), and the rate of annual cumulative costs per kW-h was studied. Complete and accurate data recorded by Hail agricultural development company (HADCO) for 39 tractors were used in this study. The analysis showed that the average annual operating hours reduced from 1558 to 1338 as the tractor age (years) increased. Also the average annual operating hours increases with the tractor power except for huge tractors where their use was limited for high draft operations only. Based on the effect of different factors on the repair and maintenance costs, multi-linear models were developed to estimate tractor repairs and maintenance costs represented by the following function. ATC = f(N,P,AHRY,kw) Where: [ATC: accumulated repair and maintenance costs, N, P, AHRY, kW tractor age (years), tractor price, accumulated operating hours and tractor power respectively. The multi-linear models compared with exponential models which were developed in previous study. The comparison showed that there is no difference between the two models for tractors with power less than 80 kW and age of 6 years or less. But for other cases the difference from the actual costs ranged between 68.8 to 8% when the exponential models used, while the estimated cost was less than 2% of the actual costs when multi-linear models used for the same tractors