1. Optimum Road Surface Design John Hine International Division TRL Limited

2. Past Solutions: Prior to road investment models the common rule of thumb was used:  0- 50 ADT Earth road  50- 200 ADT Gravel road  > 200 ADT Bitumen surfaced road

3. Modelling to Give an Optimum Solution  Highway cost models combine: Road deterioration relationships Works effects Works effects Construction & maintenance costs Construction & maintenance costs Vehicle operating cost relationships Vehicle operating cost relationships Vehicle, fuel, labour and tyre prices Vehicle, fuel, labour and tyre prices

4. What is the optimum traffic level to switch using modelling? New Research results:-  Zimbabwe 95 : 40 ADT to seal gravel road !  Zimbabwe 99 : 70 ADT to seal gravel road ! Are the results transferable ? - No Zimbabwe has a dry climate, poor (surface) gravels and low construction costs Zimbabwe has a dry climate, poor (surface) gravels and low construction costs

5. The costs of upgrading roads Cost per km

6. Conclusions 1.  There is a huge range of costs for paved roads; the costs of the bitumen surface is only a small part of the total  It is clearly dangerous to automatically transfer Zimbabwe findings to other countries  Engineers are very risk adverse and often take every opportunity to spend money to “protect” their investment, hence paved roads can end up being very expensive

7. Conclusions 2.  A lack of maintenance is no argument for paved roads: all roads need maintenance - otherwise you are just throwing away money!  Most countries only regravel about 2% of their “gravel” network each year rather than the requirement of say 17% per year  The economic window for gravel may be small (between earth and bitumen) but it depends on climate and available materials  We need to educate engineers in how to take risks and design very low cost paved solutions