"In Central Asia, traffickers have access to a well-developed road and rail network. Around 70-75 per cent of opiates are transported by truck or another vehicle across Central Asia through Kazakhstan to major cities in south-western Russia and western Siberia.108 Trains and planes usually account for approximately 15-25 per cent of trafficking. Seizures on trains have been on the rise as of 2011, particularly in Uzbekistan. Based on available data for Central Asia and Russia, in 2011 the average size of heroin seizures on trains was 6 kg, out of a reported 55 seizures (at the time of this writing). Shipments can, however, be much larger, as shown by two heroin seizures of 191 kg and 118 kg made in 2010 in the Russian Federation and Tajikistan, respectively."

Source

United Nations Office on Drugs and Crime, "Opiate Flows Through Northern Afghanistan and Central Asia: A Threat Assessment" (UNODC Afghan Opiate Trade Project of the Studies and Threat Analysis Section (STAS), Division for Policy Analysis and Public Affairs, May 2012), p. 48.
http://www.unodc.org/document…