I've been taking onboard feedback and a quality of life improvement I've added is that you can use your alpha numeric keys to quickly buy items using your upgrade points or you can click on the relevant button from the Purchase Items menu at the bottom of the screen. This saves you from having to click on the loco to buy an item.
Another exciting addition is the over powered Orbital Strike reward! You call down a high energy beam from space that deals devastating destruction to the zombie horde! To unlock this you must complete the relevant achievements, which are completing Tunnel of the Dead and City of the Dead in under ten minutes and unlocking the currently available locomotives.
Keep on destroying the zombie hordes and good luck Choo Choo Engineers!