[en] The 12 km long Mont Blanc Tunnel, is one of the longest road tunnels. Local authorities have to state whether the general regulations for the road transportation of radioactive materials, as defined by the IAEA, apply, or whether additive measures need to be taken. Whereas an activity limit - A₂ - applies only to the content of a type A package containing dispersible materials, a derived limit applying to the whole cargo of a truck has been in use in the tunnel and can be redefined. The present paper deals with the question of the choice of a proper figure for such a limit, that might regulate the transit under the tunnel for Technetium generators (ELUMATIC III from ORIS FRANCE). The first step is a risk assessment, with the truck content as an explicit parameter. The yearly traffic is of 150 trucks, carrying, on the average, 26 Ci of Technetium 99m on a yearly basis, about 5.10^-6 road accidents might be expected, while the expected radiological fatalities would amount to approximately 2.10^-8 and the expected monetary loss would be dollars 10. The second step is the implementation of decision aiding techniques based on the previous estimates