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Now that Christmas is over an analytical test


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#1 mariner

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Posted 02 January 2012 - 10:32

Christmas is over , time to wake up the analytical brain cells for 2012 so ....

To those of you not in the UK the "Borisbus" is a modern incarnation of the iconic London red Routemaster bus ( the one you see in all the old movies etc along with London fog). The name comes from the Mayor of London who pledged to reinvent the Routemaster in his election campaign. It is built by Wrightbus of the UK.

Icon or not the old Routemaster had two big advantages - you could jump on and off the open rear platform anywhere it halted and not just official stops and being a very efficient stressed skin design it weighed only 7.9 tonnes for a full capacity of 75 passengers or so. It was replaced in London by a mixture of modern double deckers weighing around 12 tonnes also with 75-80 capacity and the MB "bendybus" articulated single decker at 17.8 tonnes but with a max capacity of 153 passengers.

The question at hand is whether the new Borisbus , based on the published fuel consumption and CO2 ouput in gms/vehicle km, represents a fundemental breakthough in vehicle efficiency.

To explain the background Transport For London (TFL) who run all these buses in the same city, track their CO2 performance in terms of gms/passenger km ( a std transport climate change impact measure). TFL buses currently achive 80 gms/pass. km with tube trains at about 60. In comparision a typical new UK car wil do 138 gms/ vehicle km ( source SMMT). With the average UK car load of 1.3 people this gives 106 gms/ pass. km. That is slightly inaccurate as the car number is combined cycle so city gms/pass km will be a bit higher.

So today the bus advantage is not huge. Ths is basically because the London buses have an average load of 19.7 passengers. So at 80 gms/ pas. km and 19.7 passengers the average TFL bus vehicle CO2 output is 1576.

However the new Borisbus has, TLF are saying, a fuel efficiency level more than twice as good as the average curent bus - 640gms per vehicle km ( versus the 1576 above). This 640gms/km is based on closed track tests meant to simulate a real bus route.

In tabular from the numbers are

current london bus average Borisbus current hybrid MB bendybus Old routemaster

weight tonnes 12.0 11.8 12.3 17.8 7.9

pasengers - max about 75 87 87 153 70

CO2 gms vehicle km 1576 640 864 1300 NA


fuel efficiency MPG NA 11.2 8.6 4.3 8.0

Since aero is irrelevant in city traffic my powertrian efficiency metric to compare the buses is kg of weight per gram of CO2 - i.e how little fuel is used to haul the same bus weight

powertrian implied efficiency 7.6 18.4 14.2 13.69 NA


I have to say I find the data very confusing in that the new bus is claimed to be 60% more fuel efficient than the avearge TFL bus but have the same weight. Also it is 25% more efficient than the existing hybrid with same weight ( and close on power). That may be true but it represents a 25% improvement in hybrid powertrain efficiency which, if true , is ground breaking.

What is also strange is that the MB bendybus is reported to have a CO2 gms/km figure of 1300 but the average fleet CO2 is higher at 1576 which is a fiigure calculated from two precise published numbers , CO2 per pass. km and passengers per bus. If I were to simply pro rate the CO2 data by fule ecnomy the MB bus would be more like 1800 gms per vehicle km which is much closer to the fleet average data in terms of the MB bus being heavier than average.

I am suspicious of the claims for the new Borisbus and I am tempted to ask TFL to explain the data but first I thought I would ask the experts here for any comments on the accuarcy of the claims and the tabualr data above.

PS sorrry for the poor tabs , it looks diffrent when you type it in !

Edited by mariner, 02 January 2012 - 10:35.


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#2 Wolf

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Posted 02 January 2012 - 18:35

In tabular from the numbers are 

						 current london bus average				 Borisbus				   current hybrid				   MB bendybus			Old routemaster

weight tonnes						 12.0							 11.8						 12.3							 17.8					 7.9
 
pasengers - max					   about 75						  87						   87							  153					  70

CO2 gms vehicle km				   1576							  640							864							 1300					 NA


fuel efficiency MPG					 NA							 11.2						   8.6							 4.3					8.0  

Since aero is irrelevant in city traffic my powertrian efficiency metric to compare the buses is kg of weight per gram of CO2 - i.e how little fuel is used to haul the same bus weight

powertrian implied efficiency		7.6							 18.4							14.2							13.69					  NA


I added the code tags and fiddled a bit (deleted few spaces here and there) to improve tabgulation... HTH

Edited by Wolf, 02 January 2012 - 18:35.


#3 Greg Locock

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Posted 02 January 2012 - 20:49

There seems to be something wrong with either the CO2 or mpg figure for the MB bendybus. The two should be inversely related.

#4 cheapracer

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Posted 03 January 2012 - 04:31

There seems to be something wrong with either the CO2 or mpg figure for the MB bendybus. The two should be inversely related.


That's called a politician factor.