[acsinuk (OP)]

Why is it that almost all the underground trains and overground buses are empty most of the time??
Well, the city must provide a scheduled train and bus services so that the old/infirmed can visit doctor or hospitals and of course children need to travel to school. 
[i]So the rate payers pay for this service whether they use it or not.[/i] So it follows that rate payers should be entitled to free transport along with all pensioners and school children and of course those on benefit need to be exempt from paying.
If TFL introduced this "free for rate payers" it could well over-crowd the transport system but improve every-ones lives by reducing car journeys and pollution.
If and only if the trains or buses are overcrowded should the mayor authorise TFL to charge rate payers a premium.  Running an empty train or bus is counter productive, a total waste of money and of course a cause of pollution.

[evan_au]

I recently saw an internet-era bus service operating in a Sydney suburb.
- It was operated by the usual state public transport service
- The bus was a lot smaller than usual
- Rather than run a scheduled route (which would be a tradeoff between a frequent service and an empty service)...
- They had an internet booking system - you say where you want to get picked up, and the bus comes as soon as it is able
- Until the requests arrive, the driver relaxes beside the road, in a strategic location where he can easily drive to the next paying passenger.

Sort of like Uber for public transport....

[alancalverd]

TFL would argue that their trains "don't pollute" because they are all electric, so someone else suffers from the pollution required to make the electricity.

Other operators can lose their franchise (i.e. your money - they are all subsidised) if they don't keep to schedule. There are a couple of famous "ghost trains" that don't stop to pick up passengers, and AFAIK there is an unadvertised weekly flight from Heathrow to Cardiff and back because the route is potentially valuable - presumably when the railways finally go broke.

I heard an excellent speaker on the radio a few days ago who pointed out that his local tube station now has a 2 person limit on  the lifts, which is OK whilst nobody is using the trains, but if everyone went back to work  by public transport, they would just get there in time to come home.

We pay for lots of things we may or may not use, and some indeed we would be pleased to avoid using. The NHS, car insurance, nuclear weapons.....It's called "society". Oddly, Margaret Thatcher, who didn't believe in society, privatised the railways so you could continue paying for them - but far better that the money should go to her friends.

[Bored chemist]

So it follows that rate payers should be entitled to free transport along with all pensioners and school children and of course those on benefit need to be exempt from paying.

No it does not follow.
I am grown-up enough to recognise that, unlike pensioners and school-kids, I am lucky enough to be able to afford my own tube fairs.
I also recognise that, when I was a kid, I got cheap fares and I hope that when I'm a pensioner I will get cheap fares again.

Did you somehow not realise that?

Running an empty train or bus is counter productive, a total waste of money and of course a cause of pollution.

It's also the only way to be sure that there's a bus when Granny needs it.