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# V. CONCLUDING COMMENTS

The deterioration of the interurbak road system in the<sup>LDCs has focused the attention</sup> of researchers on the road damage component in<sup>user costs. Consequently, considerable</sup> effort was devoted to a better understanding of<sup>the deterioration process, its impact on</sup> vehicle operating costs and the implications for road<sup>user charges. Although many of the</sup> parameters in this equation are still in dispute,<sup>one can draw on international and local</sup> experience to estimate the road damage costs in the range<sup>of c0.5 to (1.0 per ESAL -km for</sup> paved roads, and about C0.2 per axle-km for<sup>unpaved roads.</sup> Much less is known about congestion costs. To estimate<sup>these costs one has to know the</sup> speed function, to evaluate the effect of spe vehicle operating costs, to evaluate the average load of passenger vehicles and th' of passengers' tirmie. Each component of this estimate is subject to gross uncertaint -s. Still, crude<sup>estimates indicate t'hat interurban</sup> congestion is only a minor problem compared with<sup>the road damage effect.</sup> Newbery estimated in the Tunisian case that interurban congestion<sup>costs are one fourth</sup> the marginal damage costs (for paved roads). In the Ghanaian<sup>case, the ratio is much lower,</sup> 1:30. The ratio is sensitive to differences in traffic (the<sup>Tunisian average volume is more</sup> than three times that of Ghana) and the value of time (the value<sup>used for Tunisia was $2.85</sup> per veh.-hour, which is exactly twice the value<sup>used for Ghana).</sup> A looming problem in the LDC context is that of urbarn<sup>congestion. Rapid urbanization</sup> and motorization and an inadequate infrastructure accelerate the<sup>pace at which this problem</sup> may reach its critical stage (World Bank, 1986). Relatively<sup>little is known about the extent</sup> of the problem, and for most cases the researcher<sup>has to rely on crude guesswork. (It is</sup> noteworthy that the only study mentioned in the<sup>World Bank Policy Study is the seminal</sup> work by Churchill _et al.,_ published in 1972.) Ghana may, therefore, be considered an exception. As<sup>part of its transport rehabilitation</sup> program a series of studies has been conducted on urban<sup>transport. These studies indicate</sup> that the problem in Ghana has not yet reached the ominous<sup>proportions encountered in the</sup> developed countries. It is even fa.- from the level witnessed<sup>in lower-middle-income countries</sup> such as Tunisia. The Ghanaian estimate of marginal<sup>congestion costs is only 1/15 that of</sup> Tunisia. Part of it is explained by differences in the value<sup>of time: Ghana's GNP per capita</sup> was $390 in 1987 (compared to $1,180 for Tunisia), but<sup>to a large extent it is explained by</sup> the differences in the marginal time costs. Still, the cost of urban<sup>congestion is 10 times that</sup> of interurban congestion.

Urban marginal congestion costs (per PCE-km) are<sup>estimated at one third the marginal</sup> damage costs (per ESAL-km). As a consequence, estimates of the road user costs<sup>for private</sup> cars are much lower than those of medium and heavy<sup>trucks. The exact difference depends</sup> on the estimates of the share of travel of private cars<sup>on urban roads and on the damaging</sup> factor (i.e., ESAL per vehicle) of the trucks, Our<sup>results turn out to be especially sensitive</sup>