In war-torn Afghanistan, an 8-year-old boy finds a way to eke out a living by directing traffic with a soda bottle on the road between Jalabad and Kabul, where he encounters crashes, soldiers and even ghosts. A New York Times article on the country’s “Pepsi bottle boys” inspired playwright Kevin Artigue’s drama, “The Most Dangerous Highway in the World,” coming to San Francisco this month. Artigue, a graduate of Public Theater’s Emerging Writers Group, is the first writer of non-Middle Eastern descent to have his play produced on the Golden Thread main stage.