ECONOMIC EFFECTS OF AXLE LOADING ON A HIGHWAY INFRASTRUCTURE IN A SEMI-DEVELOPED ENVIRONMENT

IN THE CASE OF RHODESIA, WHERE THE MAJORITY OF MAIN ROADS HAVE BEEN CONSTRUCTED IN THE COURSE OF THE LAST TWENTY FIVE YEARS AND WHERE THE MEAN TRAFFIC PER LANE IS OF THE ORDER OF 4.5 X 105 APPLICATIONS OF THE STANDARD AXLE LOAD 80 KN (8.2 T), TWO PROBLEMS ARISE WHEN ONE CONSIDERS THE AXLE LOAD : ON THE ONE HAND THE STRENGTHENING OF THE EXISTING NETWORK, ON THE OTHER HAND THE CONSTRUCTION OF NEW HIGHWAYS. THE AXLE LOAD LEGAL LIMIT IS AN ESSENTIAL FACTOR IN THE DESIGN OF A PAVEMENT. AT PRESENT, IT IS FIXED AT 80 KN. AN ECONOMIC ANALYSIS CARRIED OUT IN 1973 HAS REVEALED THAT THERE IS NO ECONOMIC JUSTIFICATION FOR AN INCREASE IN THE AXLE LOAD. THIS STUDY WAS UPDATED IN 1974 TO TAKE INTO ACCOUNT THE CHANGES OCCURRING IN THE COST STRUCTURE RESULTING FROM THE ENERGY CRISIS, BUT THE CONCLUSIONS REMAIN THE SAME. IT IS ADVISABLE TO NOTE HOWEVER, THAT IN RHODESIA THE MAXIMUM GROSS WEIGHT OF A VEHICLE IS 55 TONNES; THE MAXIMUM LENGTH IS 22 M. THE LOW VOLUME OF TRAFFIC PERMITS SUCH LARGE DIMENSIONS, AND THESE IN TURN PERMIT A LARGE NUMBER OF AXLES, THE LOAD OF WHICH IS LIMITED TO 8.2 TONNES (SINGLE AXLE) AND 16 TONNES (TWIN AXLE). THE OBJECTIVE, WHICH IS THAT OF A SMALL LOAD PER AXLE, IS JUSTIFIED IN THIS STUDY. ALL THE COSTS ARE EXPRESSED IN U.S. DOLLARS AT A RATE OF 1.74 U.S. DOLLARS TO 1 RHODESIAN DOLLAR.