Could Paris Metro inspire driverless Tube trains?
The Paris Metro's Ligne 1 has been automated and I've been over to the French capital to see how it's being received by commuters and ask will it ever come to London?
The trains come down the line quickly and abruptly every minute or so and they look like a more modern Docklands Light Railway (DLR) train.
What is noticeable straight away is that where the driver should sit there are passengers - it is a driverless train and the trains are very, very regular.
Barriers similar to those on the Jubilee line protect all of the platforms so when the doors open the passengers simply pile on safely without the need for staff on the trains.
This is Ligne 1 in Paris and it runs east to west and serves tourist stops like Louvre-Rivoli and Champs Elysees.
It is now nearly fully automated, bar four trains, and what has happened in a city where the unions are strong is a real eye opener.
The operators RATP upgraded the line with full negotiation with the unions from as far back as 2003 when the idea first germinated. The pay-off for the unions was drivers were redeployed onto another line and were promoted.
There were no redundancies.
The system means trains can run every 85 seconds and the number of travellers is now 75,0000 a day. RATP thinks it could reach 90,0000.
RATP says says it can react very quickly now to surges in passenger numbers and it can run with no drivers in times of industrial unrest. It costs 1bn euros to develop.
Mayor of London Boris Johnson said in early 2012 he wanted to see an automated system in London to rival "Asian economies".
If London is serious about more automation and perhaps no drivers at all - and the Mayor has said that - then this is the kind of model that would be under consideration.
London Underground (LU) has watched Paris with interest.
LU's current policy as it stands is more automation with staff on board (perhaps not in the cabs) but it concedes some lines, not deep level lines like Waterloo & City, could be suited to staff-less trains.
It is at the start of a journey Paris began a decade ago and is gauging reaction carefully.
However, there are differences and obstacles to bear in mind.
Ligne 1 is not a deep line, the tunnels are well lit and they are very wide. There are also large numbers of security staff around on platforms and the stations are very close together.
RATP believes staff can be at any stranded train within five minutes.
Parisians I spoke to seemed pretty happy with automation although some did say they preferred having drivers. More automation is likely in the future.
Then there are the unions.
The transport union National Union of Rail, Maritime and Transport Workers (RMT) will not support moving drivers from the cab into the carriage.
It says safety is crucial and drivers need to be in the cabs and it says it will strike over the issue.
Memories of the 7 July London bombings and the Kings Cross fire are, of course, still raw and many would baulk at unmanned trains in the capital.
But there could be storms brewing on the distant horizon and it won't just be left to the engineers to replicate Paris.
Over the next 10 or 20 years it will probably be decided in the court of public opinion and how that influences future mayoral policy and voters - and how much political will there is for a fight and an even bigger billion pound bill.
Would you want to see unmanned Tube trains like Paris?