The Neyshabur train explosion in Iran comes as a severe blow to a country that has been working hard to modernise its rail network.
By Robert Plummer
BBC News Online
In recent years, the Islamic Republic has embarked on the world's second-largest railway construction programme, in an effort to improve internal links and boost its standing as an international trade route.
The disaster was caused by an explosion of volatile chemicals
With its major industrial regions and population centres in the north and its major ports on its southern coastline in the Gulf, Iran needs a transport network that can cover vast distances.
However, railway construction has traditionally lagged behind road-building.
Iranian Railways is aiming to change all that, with a huge series of projects set to add more than 3,000km of track to the existing 10,000km.
"It's quite a big country physically and there are huge gaps in the network, which they are plugging," says David Briginshaw, editor-in-chief of the International Railway Journal.
"They see this as a way of improving the economy and improving Iran as a transit country."
In December, Mr Briginshaw travelled along the Tehran-Mashhad line on which Wednesday's disaster happened.
He says that far from being a neglected part of the railway system, it was actually one of the most modern lines in Iran.
"It was just recently improved and upgraded from single to double track," he says.
Iran may be facing a period of political uncertainty as the country approaches controversial parliamentary elections, but its economic policies are clear.
Iran's railway expansion programme is part of a wider effort to take advantage of the country's strategic position at the crossroads between East and West.
The new lines are designed to improve links with Iran's neighbours and turn it into a major route for trade between Europe and Asia.
Tehran is particularly keen to expand economic relations with the former Soviet republics in central Asia and the Caucasus, as well as Russia.
However, all this has meant a big increase in the amount of cargo handled by rail in Iran.
The Neyshabur train disaster, caused by an explosion of volatile petro-chemicals, is a grim reminder of the fact that new economic opportunities can also bring new dangers.