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Children are returning to school and Prime Minister Boris Johnson wants people to return to workplaces, making public transport services busier.

But what are the risks of catching Covid-19 on trains, buses and planes?

How safe are trains and buses?

A lot of the potential risk of infection on trains and buses depends on how crowded they are and how far away you can keep from other people at stops, stations and on board.

Coronavirus spreads when an infected person coughs, sneezes or exhales small droplets packed with the virus into the air.

These droplets can enter the body through the eyes, nose and mouth, either directly or after touching a contaminated object.

The risk indoors, in enclosed spaces, is higher than outdoors.

Indoors, good ventilation helps - so being able to open a window on public transport can be an advantage.

In England, the government's message is now to stay 1m or more apart from people outside your household.

While it's known that the virus can contaminate surfaces in enclosed areas like on public transport, it's not certain exactly how often that actually translates to a new infection.

Some groups have attempted to model the risk on train carriages - but key questions remain unanswered.

Older research has suggested a link between commuting on the London Underground and the likelihood of catching respiratory illnesses.

Dr Lara Gosce, at the Institute of Global Health, says her research (published in 2018 showed people who used the Underground regularly were more likely to suffer flu-like symptoms.

Keeping a distance, wearing a mask and avoiding touching surfaces (or washing your hands if you do), can all mitigate the risk of infection.

What can I do to stay safe on public transport?

Government advice is now that people ''can help control coronavirus and travel safely by walking and cycling, if you can. Where this is not possible, use public transport or drive" .

From 1 August, employers in England have had discretion over staff returning to the workplace, replacing the advice to work from home where possible.

Travellers are advised to:

• Travel at off-peak times
• Take a less busy route and reduce the number of changes
• Buy a ticket in advance where possible, or use contactless payment
• Keep at least 1m away from people "where possible" and take "suitable precautions"
• Wash their hands for at least 20 seconds after completing their journey

Face coverings are mandatory on public transport across the UK.

People should only travel in areas under local lockdown if their journey is essential, while the clinically extremely vulnerable should only travel if they are able to shield at the same time.

What safety measures are travel operators taking?

Transport for London has installed hand sanitisers at all tube, rail and bus stations and has also introduced a rigorous cleaning schedule. It is also asking passengers to avoid rush hour if possible.

Network Rail, which owns Britain's rail infrastructure, has been carrying out "deep cleans" and making changes in stations so people can maintain social distancing.

Rail operators like Avanti West Coast is running more trains to help with social distancing, has installed hand sanitiser points and introduced regular cleaning of trains and stations.

Arriva Buses has encouraged the use of non-cash payment methods or the exact fare in cash.

Avanti West Coast trains is working to government guidance around social distancing and the 1m plus rule to decide which seats to make available.

What is the risk on planes?

The air on a plane may well be better quality than in the average office (and almost certainly better than a train or a bus).

Prof Qingyan Chen, at Purdue University in Indiana, estimates that the air on a plane is completely replaced every two to three minutes, compared with every 10 to 12 minutes in an air-conditioned building.

Most planes have something called a high-efficiency particulate air filter (Hepa). This system can capture smaller particles than ordinary air-conditioning systems, including some viruses.

It mixes fresh air from outside with the air already in the cabin. Many ordinary air-conditioning systems recirculate the same air to save energy.

However, it may be harder to distance from others on a plane, which increases the transmission risk.

It's difficult to generalise about the risks on any form of transport because there are various factors that increase or decrease the risk.

For example, on a long-haul flight passengers might move around more and, should they have the virus, risk spreading it further.