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Acceleration consumption vs cruising consumption of bus/truck

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caliskan1

caliskan1

Civil/Environmental
Joined
Nov 28, 2021
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I need to calculate the increase of consumption of a municipal bus if average distance between stops is halved e.g 125m instead of 250m. There is no regenerative braking on the buses. I'm assuming average traffic speed is the same. Acceleration and deceleration will be the same. Routes will be the same. I think instant consumption graphs (unit fuel per sec.) of NEDC or similar lab cycles would help but I couldn't find any. A comparison of acceleration period and cruising period consumption of buses or dump trucks or similar diesel/CNG vehicles would help. Citing a resource would help. I'm trying to argue against shortening the distances on basis of fuel consumption increase, so I need citeable data to base my rough estimate on. Jumping on a bus and following the on board computer (which doesn't exist or I don't trust anyway) for a few minutes is not an option. Thanks in advance. Sorry if I'm on the wrong page.
background: I'm a civil engineer.
 
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Well, for a rough idea, with a couple of simplifyng assumptions, the consumption will be about double.
Assumption 1: Acceleration profile is the same in both cases and maximum speed reached is the same.
Assumption 2: Fuel used during cruise at steady speed is negligible. Ditto for the fuel used during idle while stopped.

With these two assumptions, the number of accelerations is doubled, so the fuel consumption is doubled.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
 
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The proper way to do it is with the BSFC map of the engine, and a bit of modelling. I used to do it by hand as an intern, as a result of which I wrote a Fortran program to do it, which was still being used several years later. Of course the bleeding obvious thing to do is to instrument a bus and take it for a trip. After 375m you have your answer.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376
 
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A good starting point would be to log speed and distance versus time for the current route. Once that is in a spreadsheet it is straightforward to calculate the energy consumed per acceleration cycle and also to test your assumption that the energy per acceleration will be the same with more frequent stops.

I am pretty sure that won't be the case. Standstill to V to standstill over 125m in a bus suggests a very small value for V.

Don't worry about BSFC initially. It won't be much different so energy usage will be a good indicator.

I reckon consumption (and time to complete the route - ie wages) will both increase by about 50%

je suis charlie
 
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... and, if the route is nearing capacity of the bus, you'll need more buses, since they'll each have lower throughput owing to taking longer to complete the route.
... and, passengers are going to notice the increase in time to get to their destination. Customer satisfaction will go down.

Normal walking speed is about 1.5 metres per second. With 250 m between stops, you're not more than 125 m to the closest one. Cutting that in half saves about 40 seconds of walking time in the worst case. Won't take too many extra stops slowing the bus down to make the total travel time longer ...
 
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And if we're going to look at every aspect, maintenance cost per passenger mile will go up sharply (since all the conditions that cause wear & tear are nearly doubled).

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
 
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I suspect that fuel will be less impacted than maintenance costs.
Even if fuel goes up 50% my hunch is that break life will be cut by 50%.
I have always been surprised that there are not hybrid trash trucks out there.
With hundreds of short accelerations a day it would seem to be a good fit.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
 
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You may have usable data already.
Do you have other bus routes with longer or shorter distances between stops and are fuel and repair records kept in such a way as to be usable?


--------------------
Ohm's law
Not just a good idea;
It's the LAW!
 
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