TSOGTTSETSII, Mongolia (AP) — After years of testy debate, Mongolia broke ground this spring for a railroad that will haul coal across the pebbled Gobi desert to China, but with one costly condition.

Citing national security, the government ordered the rails be laid 1,520 millimeters apart, Mongolia’s standard gauge inherited from the Soviets. The width ensures that the rails cannot connect to China’s, which are 85 millimeters (about 3 1/2 inches) closer together. So at the border, either the train undercarriages will need to be changed or the coal transferred to trucks, adding costs in delivering the fuel to Mongolia’s biggest customer.

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