- 13 -

The differences between urban and interurban traffic are not confined only to volume; it is also reflected in the mode distribution (Table 7). Whereas cars and pickups constitute less than 40 percent of interurban traffic, they (including taxis) account for 70 percent of urban travel. The share of buses and trucks, on the other hand, is one half of interurban travel, but only about one fifth of urban travel. The share of cars is even higher in Accra, whereas heavy vehicles play a somewhat more important role in the smaller cities.

The volume of traffic (and its distribution) is one of the determinants of the road externality, the other determinant is the traffic loading. The destructive effect of the vehicle on the road paving is an increasing function of the axle load. It is measured in terms of Equivalent Standard Axle Loads (ESALS).' The average ESAL per vehicle depends on the fleet composition (i.e., the share of heavy trucks), the legal axle-load limits and the prevalence of overloading. Early studies (TecnEcon, 1988a) found that overloading on heavily-trafficked routes was rampant and that the average equivalent axle load for 4- and 5-axle articulated trucks exceeded 20 ESAL per vehicle. Later surveys conducted by SWKP (1988a) reported lower values of 11 ESAL per truck. Needless to say, these loadings are much higher than results reported for other countries. Given the high share of heavy trucks in interurban traffic (14 percent), even the low SWKP estimate results in an average ESAL per vehicle of 1.5.

More recent studies reported by Bhandari (1990) indicate that the problem of overloading may not be as extreme as originally conceived (Table 8). Still, although the axle load of heavy trucks is comparable to the experience of other countries, their large share results in an average per vehicle which is very high. The 0.9 average, based on Bhandari's figures, is 2.5 times that reported by Newbery for Tunisia (0.38 ESAL).

Transport taxes in Ghana are in a state of constant flux. The government employs the - whole spectrum of standard taxes on vehicle acquisition, on inputs (fuel, tires, parts, etc.) - levies license fees, and collects tolls. Although the tax structure changes annually, the overall trend since the early 1980s has been one of lowering transport taxes. The SWKP (1984) estimate for 1981 is that the tax component in the price of private cars exceeded 75 - - percent, for light commercial vehicles over 50 percent, for buses 33 percent, and for trucks - 33 percent to 60 percent. The tax component in the retail price of fuel was - 25 percent to 30 percent, and in the price of tires 40 percent. In comparison, customs data for 1988 reveal that the average effective combined import tax (duties, purchase tax and penalties) per vehicle imported during the first 9 months of 1988 ranged around $450 for pickup trucks and cross-country vehicles and around $720 for saloon cars, i.e., less than 10 percent of their retail prices. The tax component in the price of fuel has dropped to 15 percent (for premium gasoline and diesel oil) and in the price of tires to less than 20 percent.

' The standard unit is an axle load of 8.2t per axle. It is generally accepted that the destructive impact of the axle is proportionate to the fourth power of the axle load [i.e., the ESAL equals (axle load / 8.2)4].