The basic problem is with the supply situation of both the British and Japanese in Malaya, is what is a railway? Just because you have access to a rail line doesn’t mean you have access to a functioning railway, if you don’t have access to all the rest of the resources that go to make up a railway. In addition to the rail line you also need, the staff to operate it, maintain it, and maintain the infrastructure and equipment. You can have the rail line, but without the rolling stock, all you have is some steel lines that you can not use, and a track bed that isn’t much use for moving supplies along. In Malaya the British have all the advantages, it’s their railway and unless they leave everything to the Japanese, and do not sabotage it as they pull back, the Japanese don’t have a lot. If the British during their withdrawal take all of the rolling stock and engines with them, along with the staff, plus demolishing some bridges, they have left the Japanese next to nothing. As the Japanese will have to import equipment from Thailand along with the staff to operate it, and find the labourers to repair any damage done. The British have all of the vital equipment and materials, plus the trained staff, to even during war time, keep their part of the railway running. At this time the motive power is steam, and this requires access to a supply of suitable coal, which the British have, plus a system to supply it, which they also have. You need maintenance and repair shops, and the skilled workers to operate in them. Unless the Japanese bring a number of skilled military railway companies with them and a source of fuel, the railway that they capture is basically worthless to them. Where as, provided the British keep their head and follow the plan, an area where all the advantages lie with them, and they should be able to operate the railway under their control, and keep it running. Which means that their logistics will be at worst adequate at best good in comparison to the Japanese whose logistics will be poor to ramshackle.