Mayoral hopefuls differ on best route to transport goals
Transport for London (TfL) has an annual budget of about £11bn, of which 42% comes from fares - meaning it is an extremely important area for mayoral policies.
On Wednesday we had two big announcements on transport; but there are still questions.
Both Labour's Sadiq Khan and the Conservatives' Zac Goldsmith recognise the importance of protecting investment in transport for things including Tube upgrades - to the tune of £3.9bn a year.
Both want the expensive Tube upgrades, new trains and for TfL to take over rail services; but there are differences in how they think it should be achieved.
Labour will freeze fares at 0% for four years.
TfL has warned that would cost it £1.9bn over five years, but Labour says it'll cost £452m over four years.
Both figures use different inflation assumptions to calculate the loss in fares revenue.
We don't know what the actual figure will be, so therefore it's difficult to know what impact that would have.
The Conservatives say Labour's plan would leave a £1.9bn 'black hole' in TfL's business plan.
But Sadiq Khan opened up another potential source of income and piled into TfL, calling it "flabby" with a "culture of excess".
And so on top of a £2.8bn cut to TfL's government grant and £15.4bn efficiencies already in the business plan by 2020-21, more savings could be needed at TfL.
The feeling is TfL has been protected so far from cuts.
A question of trust
TfL will have to work with whatever budget it is given. The question is how much can you cut its budget without it affecting investment? How much flab is there?
Would some investment have to go or be delayed? Would even a £1.9bn cut over a £50bn budgetary period until 2020-21 be achievable?
On the other hand there is the reticence of the Conservative camp, which will only say they will "bear down on fares" - replicating exactly the phrase used by the departing Mayor Boris Johnson.
That usually meant fares were kept at inflation (RPI) +1%, so Labour says the Conservatives will put up fares 17% over four years.
The Conservative policy emphasises how investment will be protected, but voters have no idea what will happen to fares. And there is a feeling from some commuters that fare rises are not sustainable.
In effect, we are being offered fares policies with a lot of assumptions and unknowns, and it will mean voters will probably have to rely on who they trust more.