Counting the climate costs of abandoned shopping trolleys

Despite the regular growth of online purchases, the majority of the British public still prefers to buy grocery products at the supermarket.

Shopping carts can help us shine our shopping in the car, but some buyers obviously prevent them further. In 2017, 520,000 carts were abandoned in the United Kingdom. Sunderland, in northeast of England, only reported 30,000 abandoned trolleys between 2020 and 2022. Similarly, 550 carts were collected in a single day in west of Sydney, Australia.

Supermarkets use a range of methods to stop carts leaving their premises, including room locations, vertical bars (to stop the carts leaving the workshop), wheels locking mechanisms and parking goalkeepers. Despite these efforts, abandoned trolleys still burn the landscape and must be collected.

Many supermarkets use commercial collection services, such as Wanzl Trolleywise or TMS Collex. These companies generally use diesel vans to study suburban areas, collect carts and return them in supermarkets. They also offer to renovate altered or damaged carts, sometimes by applying a zinc -based coating to protect against corrosion – a process known as the treat.

We are researchers from the University of Warwick who wanted to understand the environmental impact of the abandonment of carts. So we decided to investigate.

Collection against manufacturing

How does the environmental impact of the use of vans to save abandoned carts compared to the loss of these carts to excessive damage or corrosion and to make new ones?

Our study used a standardized methodology known as the life cycle assessment to analyze the potential environmental impact of abandoned shopping cart collection and management in a Coventry area, a city of English West Midlands, which includes our university campus.

We spoke to carriage suppliers, who told us that the trolleys used at the Coventry supermarket were most likely made in Spain. This was incorporated into our model.

Thanks to conversations with the Department of Successions of our University and the commercial collection services, we have established that around 30 trolleys were collected on average in the region surrounding the Tesco supermarket in the Cannon Park shopping center.

Our model assumed that a bulk transport of 50 carts is sent twice a year to be renovated, in a 220 km round trip between Coventry and a renovation installation based in the United Kingdom which was noted on stickers placed on renovated carts.

TVs collecting 520,000 trolleys abandoned in one year could issue the equivalent of 343 tonnes of CO₂ (the annual equivalent of driving of 80 petrol cars). If we imagine that 10% of these 520,000 carts have been left outside for too long and must be registered, then the total impact of global warming increases by 90% to the equivalent of 652 tonnes of CO₂ (roughly the same as 152 petrol cars conducted for a year).

It is a fairly surprising increase for such a small number of carts. This suggests that the real problem lies in the environmental impact of manufacturing.

Most emissions can be avoided

We found that a cart should be collected 93 times by a diesel van to have the same environmental impact as the manufacture of a new one.

Our results have shown that the emissions incurred during the Diesel vans collection phase were only 1% of the impact of manufacturing, and the regularization stage was only 8%. We could ask ourselves if the passage to electrically power supply vans could help. Although the emissions are reduced, the impact of the use of Diesel Vans is still tiny compared to that of the manufacture of new trolleys.

We found that the highest environmental impact came from manufacturing, which was mainly attributed to the manufacture and replacement of the steel frame of the cart.

These results strengthen the advantages of following the principle of the circular economy to keep the trucks in use as long as possible, and to avoid manufacturing to replace those abandoned.

Would something change if we were going through plastic trolleys? Other researchers have studied the effect of the evolution of trolley materials and have found that polymers have many advantages compared to steel: they use less materials, are less dense (an advantage for collection vans which emit less by driving lighter products) and do not require protective coatings, which themselves have an environmental impact.

However, if these polymer trolleys were to be sent to the discharge (or left to deteriorate in the environment), they could release carcinogenic chemicals, as well as microplastics, while they decompose. This brings us back to the importance of keeping the products used.

The abandonment of carts is bad for the environment, with a potential impact of global warming equivalent to 0.69 kg of Co₂ to collect a cart and return it to a supermarket. If we multiply this by the 520,000 trolleys abandoned per year potential, this figure becomes quite important.

Prevention of the abandonment of the cart should be a priority not only for supermarkets, but also for the general public. However, once a cart is abandoned, it is much better to collect it and renovate it than drop it out of use and make a new one, because 92 to 99% of the environmental impact can be avoided.

If it is unlikely that we can stop the abandonment of the carts, we hope that the next time people will see a cart in an alley or a park bush, the potential environmental impact of the loss of this service carriage will be apparent.

This article is republished from the conversation under a Creative Commons license. Read the original article.