You’ve reached the end of the central Thai floodplains, and are about to start going up, into the Thai highlands.
The hills ahead of you are actually the foothills of the Himalayas. They link through Laos, Burma, and China, all the way to the top of the world – Mt. Everest.
The group of mountains is called the Phi Pan Nam Range. Its composed of many smaller mountain chains roughly aligned in a north-south direction in its northern part and, further south where we are, in a northeast-southwest direction.
The highlands are characterized by a pattern of generally steep hill ranges, intermontane basins and alluvial gorges. Although the highest elevations reach little above 2,000 metres (6,600 ft), the valley floors ranging between 200 and 500 metres above sea level, so it makes for dramatic landscapes. Over to the East, towards Laos, the divide to the Mekong basin, the peaks and valleys are even more extreme, with rivers sometimes cutting deep rocky gorges.
All this means that you are going to be going even slower! Which can be good or bad, entirely depending on your attitude, and perhaps who you’re sitting next to.
The Khao Phlung Tunnel
The part of the of the railway proved to be the most difficult and expensive in the whole railway building program of Siam. The metals had to be lifted 600 feet in the course of the 27km journey from Uttaradit. The broken character of the mountainsides rendered the digging and earth-moving tasks technically complex and hard-going. And due to exceptionally high transport costs from Bangkok to here, earthworks was favoured, and tunnels and bridges were built only in exceptional circumstances.
This tunnel is one such exceptional scircumstance. It goes Its for 362.44m through pourous limestone, and it needed to be reinforced with concrete to stop water pouring into it. It runs 70m below the top of the Khao Phlung pass, where an wagon road was the only other way of getting goods to the towns on the other side of this range.
To give you an idea of the impact of this tunnel, the caravans that took goods over this high wagon road on the Khao Phlung Pass stopped running immediately after the opening of this tunnel with the first freight train on the 1st of June 1911. The price of transporting a tonne of goods over this range dropped between 90 and 99% when sent by train. A similar effect was felt as the line continued to be built through the next mountain ranges.