Dear Mr Stobart,
ENERGY EFFICIENCY AND CO2 COMPARISONS OF PUBLIC TRANSPORT VEHICLES
It was good to meet you yesterday at SET offices. As I mentioned there is an issue about the energy efficiency of public transport vehicles which you might be able to clarify for us.
I have urged James to publish comparison data on Sustraco website to show the energy efficiencies of different public transport vehicles. I am also discussing the issue in relation to work Temple Group is undertaking for clients in the railway industry.
On behalf of Sustraco I also made a submission to the Government of Australia Senate Standing Committee on Rural and Regional Affairs and Transport parliamentary inquiry into “Investment of Commonwealth and State funds in Public Transport infrastructure and services”. This energy eficciency issue is well stated in their report of Aug.09. I quote from para 3-33 pages 23 / 24 and footnote 28 thereto :-
“ Urban buses, trams, and trains use about a fifth to half as much fuel as cars per passenger km., depending on the mode and conditions. Estimates appear to allow for actual typical load factors in service, however details are mostly unclear. The estimates in different sources differ significantly: a fifth to half covers [only] most of the range. Public Transport Users Association [Australia] 2009b gives the clearest explanation: it estimates energy consumption in megajoules per passenger km; including an allowance for energy embodied in making the vehicle as :-
*train with 400 people ……0.2
*tram with 20 people………0.8
*bus with 10 people………..1.4
* car with 1.1 people……….4.7 “
Clearly for non technical non specialist readers this is confusing and potentially misleading. I also think it has the wrong for comparison measurement.
Although I have nowhere seen the issue so clearly stated for U.K. I am aware that although the numbers are different the calculation procedures appear to be similar; and the stated comparison numbers are I am sure equally dubious and confusing. For example both DfT and TfL have on their websites comparison data for CO2 emissions per passenger km. for different public transport modes and vehicle types (and there are others from consultants). On the DfT site while a range of values is given for different train and bus types only a single value is given for all tram types.
The criticisims I have of all these and other data comparison sites are :-
1. There are errors due to proxy measures such as for example fuel cost for fuel burn and passenger ticket sales for total passenger trip kms with questionable conversion factors.
2. Different operators, vehicle manufacturers and interest groups use different calculation formulae.
3. There is no independent validation and reconciliation of different primary data sources.
4. Some vehicle fleet operators have deliberatly over hyped their comparison claims in order to gain advantage in competitive tendering ; e.g. supporters of “megabus”.
However the measure of CO2 emissions per passenger km. is the wrong measure anyway because it includes two independent variables:-
*the technical capability of the vehicle , which is fixed and
* the vehicle capacity utilisation in use which is not only variable but can be manipulated by both operators and public subsidies.
For example if subsidy to a railway branch line or marginal bus route is increased there is normally a requirement to “improve” the service. In practice that usually means more empty seats traveling more frequently; and hence higher CO2 emissions per passenger km.
The measure that should be used is energy and or CO2 emissions per seat km., or per unit of licenced passenger capacity. It is also hopelessly misleading unless other variables in the comparisons are also standardised ,or at least acknowledged. The independent variables which in my opinion need to be standardised to give meaningful results are:_
1. vehicle size which matters because of economies of scale
2. Average line speed over say 100 km.
3. Number of intermediate stops
4. Age of vehicles
5. Route speed variability due to congestion gradients etc
6. Vehicle life / replacement frequency
For example maga buses only emerge as a misleading “best” in some comparisons because it is asumed that all vehicles are new, there are no intermediate stops, they operate on congestion free motorways in cruise control mode at optimum engine revs. And every seat is occupied with no subsidy penalty for occupancy rates; while simultaneously assuming that railways and trams can have none of those advantages; and vehicle replacements are not considered.
What we as tram promoters need is proper comparisons of new vehicle capabilities. After all every new model of house in U.K. now has to have an independently assesed HIP energy performance certificate covering both energy and CO2 emissions. Independent variables are standardised; and for example it is assumed for assesment purposes that a 5 person house is fully used by 5 people. Moreover once reliable performance data per seat km. are available anybody can then easily calculate the effects of different % vehicle capacity utilisations; including overcrowding and licence excedences.
Is it not reasonable and necessary to do the same for every new model of Public Transport vehicle, when it is given an operating licence?
Is this a task for the new Eco Centre for future sustainable transport?
I would be very grateful for any comments and advice you might like to offer
Dear Mr Stobart,