Spring 2009

So it's true. Home shopping really is 'greener' than shopping by car, or even by bus. The well-trailed final version of the report from Heriot-Watt University, Carbon Auditing the Last Mile, confirms preliminary findings published last year.

It's pretty unequivocal. Buying a single non-grocery item online can produce up to 24 times less environmental damage in carbon emissions than driving to the shops to buy it, the report shows. The relative figures are 181g of CO2 for home shopping and 4,274g CO2 for the car trip.

Interestingly, if you assume that a typical home delivery actually consists of more than one item, the figures diverge even further. At 1.4 items per consignment, the report finds that home delivery is 32 times less polluting; at 2.5 items it is 59 times less polluting.

If you go shopping by bus, the trip generates seven times more carbon emissions than home shopping, and up to 18 times more if you assume a home delivery consignment size of 2.5 items.

 

While the report acknowledges that home deliveries can be less efficient in sparsely populated rural areas, it even debunks some misconceptions here, pointing out for instance that making a special dedicated trip to a distant shop by car is over 70 times less efficient in carbon terms, at 13,358g CO2, than having the item home-delivered, at 181g CO2 – assuming the item is delivered first time, and the buyer keeps it.

However, the report does not set out to defend home deliveries, and it makes numerous caveats about its conclusions. For instance, the 24 to 1 carbon emission ratio for high street versus home shopping assumes a successful first-time delivery, and the report points out that the failure rate can actually reach 25 per cent or worse.

It also finds that shopping by bus at peak times (including Saturday afternoons) can compare much better with home shopping. If you share the bus with 29 other passengers and buy just five things, the carbon emissions match those of home shopping. 'Bus travel for shopping purposes needs to be promoted,' it concludes.

The writers take pains to consider wider implications too, such as combining shopping trips with other journeys ('trip chaining'), which reduces the carbon impact of the shopping trip; and using the car for something else instead of shopping (which undermines the benefit of home shopping).

The report raises unexpected doubts about the 'greenness' of courier deliveries made by locally-based part-time workers using their own cars. It says that given their relatively low drop rate compared with vans and their relatively inefficient car engines, they can generate six times the carbon emissions (417g) per delivery of a city centre van-based delivery. This assumes they are collecting the goods from a depot first.

However, the report points out that couriers achieve a much better first-time success rate than vans, and often 'chain' their journeys to include other activities, reducing their carbon impact.

The report make a various recommendations, which range from maximising carriers' drop densities ('something that is likely to happen anyway') to use of reception boxes at people's homes and separate collection points (possibly at shops passed as part of a daily routine journey) to eliminate failed deliveries.

It advocates greater use of electric home delivery vehicles, which reduce the carbon footprint much further, but says use of courier drivers in cars 'should be discouraged' unless their deliveries are combined with other journeys.

The last paragraph of its conclusion is unequivocal. 'On average É in the case of non-food purchases, the home delivery operation is likely to generate less CO2.' It adds: 'This environmental advantage can be reinforced in various ways if online retailers and their carriers alter some of their current operating practices.'

• Carbon auditing the 'last mile': modelling the environmental impacts of conventional and online non-food shopping by JB Edwards, AC McKinnon and SL Cullinane runs to 43 pages. It was produced and published by Heriot-Watt University under the Green Logistics programme.