(Bristol Parson Street 21.6.2011 - copyright Steve Sainsbury)
I was googling 'reduced traffic levels fuel prices' but soon reached this which is a useful chart of energy efficiencies. Some of the text also underlines what we've been saying for years!
Transport - source
At the end of 2002, the UK government admitted that its target reduction of 6% in road congestion by 2010 would not be met. The increase in road use was explained by the growth in the economy. The number of new car registrations peaked in 2003 falling by 7% by the end of 2007. The number of commercial vehicle registrations, remained virtually at the same level from 2004 to the end of 2007. Bus and coach registrations peaked in 2006, falling 6% by the end of 2007, bringing the total vehicles on UK roads to around 31 million cars and 4¼ million commercial vehicles.
To control congestion local authorities have been granted powers to apply various charging schemes to limit traffic in cities and in London a successful scheme was introduced. Perhaps if the fuel escalator tax had not been abandoned in 2000, but had been increasingly applied, sales in cars might have fallen and congestion restricted by higher costs. Indeed, the escalator could have been ramped up until it had a demonstrable effect on congestion. However, it has been suggested that it would take an increase of 5 times in fuel prices to make a noticeable effect on road use. The fall in new car registrations over the 5 years to 2008 was probably due to lack of road space more than high fuel prices.
But air traffic has increased and the skies are also congested, while the railways struggle to cope with more passengers than their carrying capacity. Two of the three principle forms of transport currently rely on oil-based fuels, the amount of which is finite. By consuming fuel at an ever increasing rate, the time when the roads and skies will empty is brought forward. Congestion will be exacerbated by increases in road and runway capacity, but will eventually be relieved when the fuel sustaining it runs out. Paradoxically the very increase in demand encouraged by road and runway building will bring forward the final turn-down, leaving empty motorways and abandoned airfields. The exception to this is the railways which could eventually be powered by sustainable wind and tidal power.
Comparison of surface transport motive energy efficiencies
Before considering various forms of transport, it is useful to estimate the relative efficiencies of those operating on the surface, i.e., roads and railways (including trams).
|Method<><> >||Overall %|
|Renewable electricity -> Transmission 90% -> Electric traction 85% (Rail and tram)<><> >||76|
|Diesel -> 46% ->Electricity 90% ->Electric traction 82% + 21% (Diesel-electric-battery train) *<><> >||55|
|Diesel engines; Average 46% (Road and train)||46|
|Diesel -> 46% -> Electricity 90% -> Electric traction 82% (Diesel-electric train)||34|
|Petrol engines 30-38%; Average 34% (Road)<><> >||34|
|Fossil fuels -> Electricity 40% -> Transmission 90% -> Electric traction 85% (Rail and tram)<><> >||30|
|Renewable electricity -> H2 44% -> Fuel cell 40% -> Electric traction 85% (Road)<><> >||15|
|Fossil fuels -> Electricity 40% -> Transmission 90% -> H2 44% -> Fuel cell 40% -> Electric traction 85% (Train)||5|
* Hitachi diesel-electric multiple unit with battery storage enabling regeneration
From the above rough estimated stage efficiencies, it is evident that rail and tram make the best use of renewable sources of electricity, whereas the use of hydrogen as a "mobile" fuel able to be carried on a vehicle is the least efficient. It is also evident that renewable electricity offers 2½ times more useful work energy that the primary energy used for fossil fuel electricity generation.