Wednesday, March 19, 2014

Blanket 20MPH Speed Limits And Traffic Humps, Causing More Pollution.

A reduction in speed from 30mph to 20mph increases CO2 emissions

According to the Highways Agency’s figures, at 30mph average CO2 emissions for vehicles stands at 188g/km, whereas at 20mph this rises to 221g/km. This is usually due to motorists driving in a lower gear than they would at 30mph.  This is demonstrated by the chart below.

This graph represents emissions with free-flowing traffic. The emissions represented are an average for all vehicles. This is the latest study representing CO2 emissions for free-flowing roads.

The graph is only available for kilometres per hour.  To assist your use, see the conversions between kilometers per hour and miles per hour below.

The AA also advise that cutting the speed limit from 30mph to 20mph on the wrong roads can increase CO2 emissions by more than 10% with the result that well-intentioned safety schemes may backfire in environmental terms.

They state that transport and highways planners have little or no official guidance on the environmental impact of 20mph speed limits and it would be ironic if local authorities that have targeted owners of larger vehicles with environmental charges, are found guilty of increasing CO2 emissions through indiscriminate use of 20 mph restrictions. 

This is priceless from Jan Piechocki, Ex Met traffic officer & accident investigator:- 
“This idea of 20mph zones/limits is getting monotonous as opposed to boring. I don’t believe that reducing the limit to 20mph will actually save lives/reduce injury, because I can cite many real instances of actual deaths under that speed, reduced damage yes, but deaths/injuries no. 

Low speed impacts can cause a cyclist/pedestrian to go under the vehicle as opposed to being pushed aside as is if a higher speed. 

As I spent 17 years dealing with accident scenes as an accident investigator I think I am qualified to make this observation. I cannot agree with some interpretation of statistics that denies that the accident rate has gone up, such as in the experimental 20mph zone in Portsmouth.

The blanket 20mph speed limit/Zone encourages drivers minds to wander, it makes conscientious drivers worry about their speedometer at the expense of their surroundings, it gives pedestrians a false sense of security, it encourages drivers to ignore the limit in areas within the zone where a higher speed is safe to do so thus encouraging contempt for the limit overall. I am afraid that the motorized vehicle is here for the foreseeable future whether we like it or not.”


        AA Fuel consumption figures

30mph/20mph/speed humps petrol car consumption figures

  • Steady 30mph (4th gear):
    60.7 mpg (small petrol car), 55.6 mpg (medium petrol car) 
    = 58.15 mpg (average)
  • Steady 20mph (3rd gear):
    55.5 mpg (small petrol car), 49.1 mpg (medium petrol car) 
    = 52.3 mpg (average)
  • Speed humps (6 over 1/2 mile at 20-30 mph): 
    33.8 mpg (small petrol car), 27.9 mpg (medium petrol car) 
    = 30.85 mpg (average)

30mph/20mph/speed humps petrol car consumption differences

  • Change 30 mph zone to 20 mph:
    increases fuel consumption by 5.85 miles per gallon, or 10.1 per cent.
  • Add speed humps to a 30 mph zone:
    increases fuel consumption by 27.3 miles per gallon, or 46.9 per cent.

The AA's fuel consumption tests were carried out at Millbrook proving ground by an independent engineer and car tester, using a fuel flow meter.

In 2000, the then Department of Environment, Transport and the Regions argued against reducing the 30 mph limit for fear of increasing emissions.


Anonymous said...

Something for everyone to take in interest or comments.

Anonymous said...

Pollution related illnesses kill 4300 people in the London area. Boris Johnsons emissions strategy has reduced polution 0 % since he took office. Miss managed traffic systems and spiralling mismanagement will surely be Boris Johnson's down fall. It's a great shame that so any are so ignorant to bring about change.

Here's Johnny said...

The truth...they can't handle the truth.

Anonymous said...

No interest in this is because there's nothing about yellow badges working in town in it.