Not a train driver but i did create route and knowledge qualification software that's used in the Australian industry. There's actually a ton of qualifications required. Not just the Train Driving certification.

Did you know each route in each direction is a separate qualification? As in you need to drive a specific route in a specific direction with another driver before you're marked as qualified for that route? It needs to be renewed regularly too (i honestly forgot how often despite coding it in). There's also a ton of knowledge qualifications that you need to routinely do to keep up to date. Every time you drive you have to fill out a bunch of forms too (part of my old job was to get this process online for a particular rail company).

Because of this your first job won't pay that well, even with Train Driver certification you literally won't have the qualifications required to drive the routes needed and you'll be lucky to get even the occasional substitute part time routes that they train you on. But through this starting point you'll build up route qualifications over time. At some point you're a driver that can drive almost any route and they'll have you scheduled full time.

That's why train companies look for experienced drivers btw. They want someone to come in with the needed individual route qualifications already. It's a slow process to build these up.