The 8ATT 2-8-4 tank engine concept is another possibility for modern steam traction incorporating some of the AT (advanced technology) features of the 5AT.
Whilst being similar in principle to 8AT conceptual design, the tank engine configuration, having no tender, is lighter and less costly than a tender engine. Furthermore, it can run equally well in both directions, therefore requiring no turning facilities. On the other hand it's more limited fuel and water reserves limit its range, but with the reduction in both fuel and water consumption offered by modern steam, a tank engine of this sort could still be expected to have a useful operating range of up to 200 km, making it a suitable machine for independent, tourist and heritage railways.
Like the 8AT, some of the more advanced features of the 5AT would not be required for the speeds and duties that the locomotive would be expected to undertake, thus offering further savings in costs. 5AT features that would not be required include:
- oil firing (unless preferred);
- combustion air heating;
- twin valves;
- light weight motion parts;
Furthermore, Network Rail approvals and all associated costs would not be involved.
The Project Planning Team has undertaken some preliminary investigations into the cost of developing a locomotive of this configuration and estimates that its cost should be around 60% of the cost of the 5AT.