As a thought experiment, the cost of supplying low-density rural areas by drones on a weekly basis was estimated for Sierra Leone. New high-end commercial drones have a range of 40 - 60km, but cheaper ones, like the ones used by nongovernmental organizations, have a range of 20km (Raptopoulos, 2013; USAID Global Health Supply Chain Program-Procurement and Supply Management, 2017). In Sierra Leone, 75 percent of the rural population that lives more than 2km away from a primary or secondary road is within 10km of a primary or secondary road, 16 percent are between 10 and 20km, and 8 percent are between 20 and 40km (only 1 percent lives further than 40km from a primary or secondary road). If drone deliveries target only low-density areas (less than 150 people per square kilometer), the cost of delivering 1kg of supplies for 10 people every week would be between $1 per person per year and $26 per person per year, depending on their distance to the closest all-season road and the drone technology used.

**Table 6** presents the results based on the assumptions that a $3,000 drone flies at 40 kilometers per hour, can carry 1 kilogram, and can fly for 8 hours. A $50,000 drone flies at 100 kilometers per hour, can carry 2 kilograms, and flies for 8 hours. Costs include the capital cost of the drones plus operating costs (including labor). Isolated population is the share of the rural population living further than 2 kilometers away from an all-season road. This results in total estimated cost of $5 million to $9 million per year.

**_Table 6_** _Estimated annual cost of delivering weekly supplies to low density areas in Sierra Leone for different maximum population densities and different drone technologies_

|**Max density served**<br>**(Population/km2)**|**Share of isolated rural**<br>**population served (percent)**|**Total annual cost in milli**<br>**3 000$ Drones**|**on $ (average over 5 years)**<br>**50 000$ Drones**|
|---|---|---|---|
|150|69|5|9|
|100|51|4|7|
|75|37|3|5|

Based on the most conservative assumptions in this analysis for Sierra Leone, bringing weekly supplies to remote areas by drone costs 3 times less every year than increasing rural accessibility from 30 to 31 percent; and 22 times less than increasing accessibility from 69 to 70 percent. Moreover, these costs are likely to go down quickly, as drone markets mature, and the number of service providers increases. Thus, at least in the short term, drone delivery could help increase social integration in remote rural areas.

# **4. Conclusion**

This study presented first estimates of global road access in rural areas, combined with road upgrade cost and strategies to explore how rural access can be increased. To do so, we used the latest state-of-the-art publicly available data sets: road network data from OpenStreetMap and global population estimates from WorldPop.

The results showed that for some countries, universal access to paved roads is not a realistic goal in the short to medium term. We thus reversed the question and asked how much incremental access can be achieved if countries spend 1% of their GDP annually on the upgrade of rural roads, beginning with those that have the highest impact. We found that, under optimistic assumptions on GDP growth, rural accessibility would only increase from 39 to 52 percent by 2030 across all developing countries. We also found that the deforestation effect that accompanies paving these roads can be significant in many countries.

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