[nicephotog]

Diesel (drained water from the fuel filter, service done on time)?

or petrol (unleaded , unleaded premium) ?

It still fluctuates so nothing mechanical. It's petrol, so I have wondered about the quality of fuels, whether light distilates are being boiled off or burned, or simply a different quality of fuel or contamination. I feel it is definatley something to do with the air, the humidity content, smog etc.

It is considered the humidity and moisture from air , BUT , the reason is the underground storage tanks at petrol stations must have a breather vent (not simply each motor vehicle). Too , it is each station must adhere to quality control but for one reason or another it can be a problem.
BUT, again finally, a diesel filter is not quite the same as a petrol filter in terms of water, truth is though to cut it short ,either will cease to allow flow to the engine fuel controls if enough water is caught.
Diesel vehicles use very good blocking filters in a filter reservoir and have a drain screw.
Diesel is coloured (refinery must add a dye colour) but water is clear and heavier.

[alancalverd]

The idea of a light railway is there are more stations and you walk to a local station.

At the age of 80, I am not inclined to walk 50 miles to the nearest London Underground station to make a 9 am meeting tomorrow. I could probably manage the 5 miles to the main line station if there was no hurry but the last time I arrived there it was closed due to strike action so I had to drive 200 miles to the job - turned out to be quicker and cheaper than the train anyway, even though it wasn't subsidised by the taxpayer (me).

Some years back a Department of Health survey discovered that there were fewer disabled people in London than almost anywhere else in the UK, with rural Northern Ireland scoring particularly high. My group was tasked to investigate the anomaly. It turned out that the definition of "disabled" was the question "Can you walk to a bus stop?"

Meanwhile, be cautious of weekly fuel consumption figures unless you drive at least 500 miles a week. Fuel tank float monitors are notoriously vague and nonlinear as the inferred volume depends on the starting level and the shape of the tank. Even if you have credibly calibrated  injectors or a flow monitor, a lot depends on the ambient air temperature at startup, and overtaking on a hill will have a startling effect: most cars cruise at around 10% of maximum power and a short burst at 100% makes a huge difference to the short-term average consumption.   

[Petrochemicals (OP)]

At the age of 80, I am not inclined to walk 50 miles to the nearest London Underground station to make a 9 am meeting tomorrow

I wouldn't call that local. It's more about the time than the distance, even if you drive you have to find a parking spot at a station, you can still have spent 10 minutes extra, may as well drive straight there at that. Even if you only live around a mile away that can still be a 20 minute plus walk in the freezing driving rain. It needs to be 10 minutes tops, ideally within 500m of your door or stations 1km apart with lines spaced similarly. Quick accelleration and breaking and you can cross a city much faster than you can drive.

[alancalverd]

1km apart with lines spaced similarly. Quick accelleration and breaking and you can cross a city much faster than you can drive

You need 30s stops at each station, and acceleration > 0.15g is not acceptable. There's little difference in practice if the city is well planned.

The real frustration with public transport is short-haul flying. I can't afford the time or cost of a train to Glasgow but although the Airbus covers the distance in 50 minutes, the overall trip door-to door takes as long as driving. Quickest, and still cheaper than the train, is the old Cessna - provided the engine starts.

[Petrochemicals (OP)]

There's little difference in practice if the city is well planned.

Triple carriageways with flyover and slip roads plus their embankments and free flow junctions, but then you get to the problem of the majority of the city consisting of roadway rather than anything else. You could tunnel, but the upheaval of the upheaval and the cost is something governments tend to shy away from. Maybe we should start building cities in the air starting with pavements at the 3rd storey.

[alancalverd]

Future "cities" will be very different. Office blocks are a 20th century excrescence from the days before telephones, there will be no need for high densities of  manual workers, most retail and all wholesale will be from automated warehouses....I think the city is doomed to extinction. And if we are to live sustainably,  a much-reduced population will be living in villages with a pub and a post office/ local government/registrar's office  where the church used to be.

[Petrochemicals (OP)]

Future "cities" will be very different. Office blocks are a 20th century excrescence from the days before telephones, there will be no need for high densities of  manual workers, most retail and all wholesale will be from automated warehouses....I think the city is doomed to extinction. And if we are to live sustainably,  a much-reduced population will be living in villages with a pub and a post office/ local government/registrar's office  where the church used to be.

Only Alan if it is cheaper, money rules Alan, bankers I think will be replaced completely, computers already do much stock trading, their is no need for an opening or closing bell now, nor do they need to be in the same area, as you say, communications render New your as Close as Canary Warf .

Modern cities are beginning to etracate businesses from the centre to the outskirts, with high density housing taking their place, even though the centre was once sensible for commuting, many people commute past their own centre anyway to another or somewhere else and businesses are not constrained in florspace or tax rates. This though is all the more reason for a good light railway system in any major connurbation.