N/a - Noise pollution from buses

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Sat 9 Feb 2013 15:07
N/a - Noise pollution from buses - galileo

Has anyone else noticed how appallingly noisy many double decker buses are now?

Around here the fleet run by FirstBus are rear engined with huge cooling fans behind a grille on the right rear, the fan noise drowns the engine sound as they pull away or grind up the many hills.

Years ago I worked on the development of temperature sensing fan drives for heavy trucks, the market for which devices had grown due to noise legislation, based on drive-by tests.

Do these limits still appply, or are buses (so beloved of our 'green' masters) exempted?

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Sun 10 Feb 2013 14:05
N/a - Noise pollution from buses - Bromptonaut

What make, model and approx age are these buses?

Round here, Northants, Stagecoach operate the inter town buses but First took over the Corporation buses in Northampton itself.

Can't say I've noticed them being over noisy but I don't live on a bus route.

I cycle in Central London where some of the buses have partial aircon; they can generate a bit of fan noise but not anything to get bothered about.

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Sun 10 Feb 2013 14:51
N/a - Noise pollution from buses - jamie745

Sensible people have known for ages that buses are the most polluting things on the road. Doing 4mpg with 3 people on board, chucking out nox gases from a stoneage diesel engine from the Industrial Revolution and as the OP says, they are ruddy loud!

Didn't Oxford decide to ban cars but lay more buses on and their total emissions actually rose? Says it all really. The attack on the motorcar is nothing to do with the environment, it's a movement against personal independence.

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Sun 10 Feb 2013 15:05
N/a - Noise pollution from buses - Bromptonaut

Oxford simply cannot absorb the number of cars that want to go there. Park and Ride worked fine last time I was there for a day's traininig at a central office,

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Sun 10 Feb 2013 15:09
N/a - Noise pollution from buses - jamie745

I've never seen a Park and Ride bus with anybody on it. The vast majority end up white elephants. No wonder the town centres are dying.

Edited by jamie745 on 10/02/2013 at 15:10

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Wed 13 Feb 2013 16:44
N/a - Noise pollution from buses - unthrottled

round here the fleet run by FirstBus are rear engined with huge cooling fans behind a grille on the right rear, the fan noise drowns the engine sound as they pull away or grind up the many hills.

Trucks don't have rear mounted engines and tend not have a stop-start duty cycle like city buses do. A mechanical fan really is the only effective solution in this case.

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Thu 14 Feb 2013 14:18
N/a - Noise pollution from buses - galileo

round here the fleet run by FirstBus are rear engined with huge cooling fans behind a grille on the right rear, the fan noise drowns the engine sound as they pull away or grind up the many hills.

Trucks don't have rear mounted engines and tend not have a stop-start duty cycle like city buses do. A mechanical fan really is the only effective solution in this case.

I accept that the operating conditions mean there is a lot of heat to dissipate, what I question is whether the drive-by noise test limits have been relaxed or if buses have a higher limit than trucks.

Apart from anything else, truck radiators and fans are at the front, so not so noticeable if you are at the side, on the pavement, while these (fairly new) buses emit their fan noise from the side. Other,similar sized vehicles of a different make have grilles across the rear and are much quieter. Maybe the issue is that radiator size has been minimised to save weight and space so the fans have to be geared to run faster?

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Fri 15 Feb 2013 00:19
N/a - Noise pollution from buses - unthrottled

Apart from anything else, truck radiators and fans are at the front,

That's because the engine is at the front! Whilst the vehicle is moving, air automatically passes through the radiator, so the fan(s) don't have to work very hard unless it's a quarry truck crawling up a steep hill.

City buses place the engine at the rear because it allows the floor at the front of the bus to be very flat and low which is a requirement for the easy access for disabled passengers. The cramped engine bay at the rear rear has to create virtually all its ventilation from a fan which has to work hard.

Disabled access will trump noise considerations, I'm afraid!

I take your point about the rear vs side mounted ventilation. At higher speeds, the rear radiator is more efficient because the low pressure region behind the bus draws air through the radiator. But at city route speeds, I doubt it would make much difference. Maybe the side mounted ventilation might be designed with driving on the right in mind?

I know exactly what you mean. I lived on a road which was on a bus route. The only traffic noise that disturbed me was a tiny little frog-eyed minibus that drove passed my house every twenty minutes. The fan drowned out the engine and was far noisier than a 44 tonne artic! As luck would have it, I lived 50 yards on the other side of a T-junction. The engine hit max revs in first gear just as it passed my window. :(

Had I lived 50 yards on the other side of the junction, I would have been completely oblivious to it.

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Fri 15 Feb 2013 22:19
N/a - Noise pollution from buses - galileo

Unthrottled, today I noticed buses from a different company which appeared to have a grille and radiator at the front - presumably like Hillman Imps they have pipework from the rear engine to the front radiator?

(The temperature-sensing fan drives we developed were all for heavy trucks, some viscous coupled, some oil-operated clutches, all capable of transmitting considerable horsepower, huge difference in sound on test beds between 'on' and 'off' states.)

We too used to live on a bus route, even double glazing doesn't shut the noise out, does it?


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Fri 15 Feb 2013 22:35
N/a - Noise pollution from buses - jamie745

I lived on a busy road all my life until I moved out at 24. Frankly the quietness scared the bejesus out of me and was hard to get used to.

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Fri 15 Feb 2013 22:48
N/a - Noise pollution from buses - unthrottled

I can't see any real impediment to piping the coolant to the front of the vehicle-even given the length). You need a considerable length of very heavy gauge cable though!). Also, the water pump would have to work a little harder which is more parasitic drag.

The rear sited engine bay itself will still require ventilation (not least for the transmission cooler and aftercooler) so you end up requiring several fans. Lots of little reasons that make it unattractive.

As you know the type of fan drive is determined by the duty cycle. Electric for light duty use, viscous coupling for medium duty and mechanical driven for heavy duty (fan use, not vehicle use). If the fan is required, say 75% of the time, a directly coupled fan will probably have an efficiency advantage over a viscous coupling.

I think the duty cycle of the fans will be surprisingly severe. A bus might only weigh 1/4 that of a fully laden lorry, but:

-They have to stop and start much more frequently.

-they accelerate much more aggresively to keep to schedule

-they use automatic transmissions with a lot of torque convertor slip.

The cooling requirements might be more severe.

Isn't part of the reason (other than blade design) for the noise, is that the fan blows air out of the bay, rather than drawing it in?

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Sat 16 Feb 2013 08:34
N/a - Noise pollution from buses - galileo

Unthrottled, as usual you provide a clear and complete explanation. On further thought, I wonder if the current front-grilles are only for air-con condensers installed at the front, or even for brake-cooling ducts, brakes are severely tested on PSV service for the same reasons, frequent stops etc.

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Wed 27 Mar 2013 17:53
N/a - Noise pollution from buses - Sofa Spud

At least the horrible whining, rattly noise made by the original Leyland National buses, with their seriously smoking Leyland 500 series engines, is no longer heard in towns and cities of this land.

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