For several years, England's capital city has charged a fee for vehicles entering a center zone, under the guise of "congestion charging".

In reality, it's a tax based on CO2 emissions, all vehicles emitting under 100 grams per kilometer of carbon dioxide allowed free passage into the center. Until now.

From July 1, the congestion charge limit reduces to 75 g/km of CO2--meaning thousands of drivers will have to pay the over-$15 daily fee to enter the city.

Transport for London (TfL), which governs the city's transportation systems, is allowing a three year exemption window for sub-100g/km cars bought before the rules come into force, but any car bought after then will be subject to the same charge as any other vehicle.

In effect, only plug-in vehicles will be exempt.

The lowest-CO2 non-plug-in vehicle currently on sale in the UK is the Toyota Yaris Hybrid, with a minimum output of 79 g/km. Toyota had originally said the car's low CO2 output should pre-empt any such limitation, but the car misses out by a mere 4 g/km.

On the other hand, Toyota's 49 g/km Plug-In Prius, cars like the 27 g/km Chevrolet Volt and its Vauxhall Ampera cousin, as well as any full battery-electric vehicle, will still enjoy exemption from the charge.

Dissuading dirty diesels

TfL's main impetus for reducing the limit was to stem the increase in diesel vehicles getting into London for free.

While diesel vehicles are economical enough to produce low CO2, and also produce low hydrocarbons and carbon monoxide, European emissions limits aren't nearly as strict on their particulate matter or nitrogen oxide emissions.

The former is responsible for all manner of respiratory diseases, the latter a leading cause of smog. With London's air some of the dirtiest in Europe, the incentive to reduce these pollutants is high.

Several European cities run similar schemes to London, with strict emissions regulations and tax breaks based on CO2 output.

The schemes make sense from an environmental perspective, but the worry for London is that with plug-ins still out of reach of most buyers, the sole incentive for buying clean hybrid vehicles and other low emission choices has been taken away.

Now, save for an arbitrary few miles per gallon difference in daily driving, there's little difference for a driver choosing between a 76 g/km car and a 126 g/km car. Previously they might have chosen the cleaner vehicle of the two for the congestion charge savings, but now they'd have to spend thousands extra on a plug-in to see the financial benefits.

Taxis, buses get a free pass

The other issue is London's public transport systems. While effective, many taxis and buses lag well behind on emissions, failing to meet regulations almost ten years out of date. A London taxi meeting Euro 3 standards can produce ten times the particulate matter of a modern Euro 5 diesel.

We welcome schemes to encourage drivers into greener vehicles, but for London, it may be some time before the new lower limit actually realizes any environmental benefits.

Of course, there's an alternative scenario--with plug-ins out of reach and regular hybrids costing so much more for London drivers to run, people may avoid using cars at all...


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