[jfdecw]

On a motorway at a steady 65 mph my diesel reports 40 miles per gallon

In congested urban traffic with traffic lights I get less than 15 miles per gallon

I am looking at the pollution effect of traffic conditions. Can anybody help? Either through experience or published data

[Rolebama]

I don't understand the govt's approach to vehicle pollution. Just about every anti-pollution devices fitted to cars reduces mpg. It makes more sense to me to improve mpg and spread the pollution caused by burning fuel over a larger area, but then I suppose the loss of fuel taxes would upset the bean-counters.
FWIW: Both my Peugeots were diesels. They could both achieve just under 70mpg at motorway speeds, and 40mpg around the suburbs. I played with all my older petrol cars with carburettors, and doubled the mpg on some of them. Simply by balancing the moving parts, and assembling with care. Rejetting carbs, amd in some cases replacing them.

[olduser]

Looking at mileage figures supplied by OP I would guess/hope it's a heavy van.
If not a van then it looks as though the fuel system needs some work or a much lighter foot on the throttle.

As far as pollution is concerned, if the fuel is being burned the pollution will be roughly proportional to the fuel used.

[NMNeil]

Would it make a difference?
After all the DPF will catch particles and the catalytic converter will do it's job no matter the speed. In fact as the exhaust and cat will be hotter in slow traffic with less air cooling, a cat would be more efficient.
As olduser said, there's something wrong with the engine.

[Drivingforfun]

I think there's a difference depending on whether you're looking from a local or a macro perspective. Some scenarios / engines mean more local pollution but less global impact. The idea of causing more pollution but keeping it away from populations (for example, going a longer way around a city rather than through it) is attractive when it comes to the former but at cost to the latter

What I'm trying to say is, it's not black and white as just looking at the numbers, but where they're applied

[olduser]

Originally Posted by NMNeil

Would it make a difference?
After all the DPF will catch particles and the catalytic converter will do it's job no matter the speed. In fact as the exhaust and cat will be hotter in slow traffic with less air cooling, a cat would be more efficient.
As olduser said, there's something wrong with the engine.

The cat needs heat to get started but it makes it's own heat after that, additional heat from the engine has very little effect. The DPF do's need heat from the engine to clear out the particles it has trapped making it dependant on the engines exhaust heat.

[Nick]

Originally Posted by jfdecw

On a motorway at a steady 65 mph my diesel reports 40 miles per gallon

In congested urban traffic with traffic lights I get less than 15 miles per gallon

I am looking at the pollution effect of traffic conditions. Can anybody help? Either through experience or published data

Hi @jfdecw - firstly, welcome to the RAC Community, it's great to hear from you.

What sort of vehicle are you driving?
And when you say you're looking into the pollution effects, what are you looking at the effect on? The environment? Health?
Let us know what you're thinking.

[olduser]

Originally Posted by Drivingforfun

I think there's a difference depending on whether you're looking from a local or a macro perspective. Some scenarios / engines mean more local pollution but less global impact. The idea of causing more pollution but keeping it away from populations (for example, going a longer way around a city rather than through it) is attractive when it comes to the former but at cost to the latter

What I'm trying to say is, it's not black and white as just looking at the numbers, but where they're applied

In the past that was the thinking, my pollution* is not a problem because the atmosphere is so vast, the wind will just carry my pollution away from me but the atmosphere is a finite size, and some pollutants have a very long life, we now find we can, and are, polluting the Earth.
CFC's were a good example, in their heyday they were freely discharged into the atmosphere, until we discovered they did not decompose but had a very long life and interacted with the Ozone layer, allowing more Ultraviolet light through.
Once this was recognised, most countries started to use other gases in place of CFC's, and now the Ozone layer is reforming.

*Including Carbon Dioxide.

[jfdecw]

2008 diesel Seat Alhambra Ecomotive. Car is regularly serviced. My quoted consumption is as reported by the vehicles's management system. My major concern is fuel consumption and traffic management: enabling free flow reduces emissions, and I argue decreases traffic violations. A red light means a RED light.
Whilst I have sympathy with some of the views expressed on the negative effect of vehicle emissions, central, local government and the Mayor of London use vehicle pollution/clean air as opportunity for increased revenue collection.
My local authority boasts the greatest combined length of bus lanes of all authorities. The latest bus lane addition is from the bottom of the A329(M) westward. The journey time has been doubled and traffic violations increased for a length of about 1.5 miles!
Consumption figures are quoted for urban and extra urban. Are quoted urban figures better than actually achieved? I am thinking short journeys on cold engines.
My feeling is that "green" policies are more about taxation (taxing you and I the ordinary consumer) than improving the health of the globe for our grand children

[Rolebama]

FWIW: Later research shows the hole in the ozone layer is a necessity. It allows for the CO2 exhaled by nearly 8 billion people to escape rather than hanging around suffocating us. It seems that most of the ozone is produced by the oceans, and I believe there is ongoing research as to what effect, if any, our pollution of the oceans is having. The hole enlarged to allow for CFCs etc to escape.
As for catalytic converters, all they really do is convert smelly sulphur-based chemicals to be converted into non-scented nitrogen-based chemicals. As for EGR and DPF they still produce the nasties, only now it is virtually invisible.

[olduser]

Originally Posted by Rolebama

FWIW: Later research shows the hole in the ozone layer is a necessity. It allows for the CO2 exhaled by nearly 8 billion people to escape rather than hanging around suffocating us. It seems that most of the ozone is produced by the oceans, and I believe there is ongoing research as to what effect, if any, our pollution of the oceans is having. The hole enlarged to allow for CFCs etc to escape.
As for catalytic converters, all they really do is convert smelly sulphur-based chemicals to be converted into non-scented nitrogen-based chemicals. As for EGR and DPF they still produce the nasties, only now it is virtually invisible.

I have read of this later, ‘research’ but I am unable to find anything published, and in the science world if it isn’t published it has no credibility.

Taking a look at what is published, the Ozone (O3) layer is very high in the Atmosphere up in the Stratosphere, while Carbon Dioxide (CO2), a heavy molecule, is down in the Troposphere.
CO2 is slowly removed by natural processes – Photosynthesis, absorption by Oceans, Weather, and some absorption by New Rocks.

The Ozone Layer was damaged by Chlorofluorocarbons (CFC), a man made gas produced for Refrigeration, also used as a propellant in spray cans, and a gassing agent in the manufacture of plastic foams.
CFC’s aided by sunlight broke down leaving Chlorine (Cl) to degrade the O3 to Cl + O2.

Catalytic Converters as used on vehicles are the three stage types, they oxidise unburned fuel (HC), Carbon monoxide (CO) changing these to CO2 + H2O, Nitrogen Oxides (NOx) are broken into N + O2.
The Hydrogen Sulphide smell should be very rare these days; it dates back to the days of high levels of Sulphur in fuel but this reduced or was eliminated as a result of the Acid rain controversy. Today, it should only happen on vehicles that don’t get their Cat’s up to working temperature.

DPF these catch soot but convert it to CO2 when regenerating.

EGR feeds exhaust back into the engine, reducing combustion temperature thus reducing the amount of NOx produced, lower combustion temperature = lower efficiency!

DEF or AdBlue injects urea solution into the exhaust; the heat changes this into Ammonia this reacts with NOx producing N + H2O.

So yes, it is fair to say that in some cases we change the pollution into another pollutant or force the engine to run inefficiently causing more pollution. This to me suggests we need another source of power for vehicles.

[NMNeil]

Originally Posted by jfdecw

On a motorway at a steady 65 mph my diesel reports 40 miles per gallon

In congested urban traffic with traffic lights I get less than 15 miles per gallon

I am looking at the pollution effect of traffic conditions. Can anybody help? Either through experience or published data

An ICE engine is most efficient when it runs at a constant speed under a constant load, the speed and load are determined by the engines design. After that it's just a compromise between performance, efficiency and emissions.
Carburetors have accelerator pumps that gave an extra squirt of fuel when accelerating, fuel injection does the same by holding the injectors open longer, and when it happens performance goes up but so do emissions and efficiency nosedives. When cruising on the motorway you are within the magic constant speed and constant load range. While stuck in traffic the engine is still at a constant speed (idle) and constant but minimal load, but every time the traffic moves and you follow, you're accelerating. Then there's how to you measure everything. Motorway and general driving it's miles per gallon, but while stuck in traffic it would be gallons per hour as there will be almost no miles moved.
Makes you wonder if you used gallons per hour for both scenarios if there would be a difference?
I can find no research on efficiency/pollution/performance changes between motorway driving and driving in congested traffic, but here's some bathroom reading for you on emissions at different speeds.
https://www.sciencedirect.com/scienc...95756424000709