LONDON (BLOOMBERG) - A national rail strike will disrupt travel across Britain on Wednesday (July 27), adding to a summer of transport turmoil that has seen airports slash flights, soaring temperatures melt roads and runways, and the port of Dover beset by hours-long border delays.

The walkout by 40,000 members of the National Union of Rail, Maritime and Transport (RMT) workers marks the fourth day of action by the labour group this summer and comes ahead of further Britain-wide strikes by the RMT and two other unions in the coming weeks.

With Dover facing another busy weekend as the end of the school year triggers the peak summer exodus, British Airways pilots pressing for a new pay deal and London Heathrow airport warning that a passenger cap could remain in place through next summer, there is little sign of relief for beleaguered travellers.

And while Britain may be the epicentre of the chaos, most of Europe is suffering, with Deutsche Lufthansa revealing that it will scrap almost all flights at its German hubs on Wednesday as ground staff walk out.

Here is the latest news on the strikes:

How long will the rail walkouts last?

RMT members will strike at 14 train operating companies for 24 hours from midnight. Their action at Network Rail, which owns tracks and stations, starts at 2am.

The walkout will shutter half of the British rail network completely, with only about 20 per cent of trains operating on what is left, limited mainly to intercity services and a smattering of commuter routes. Trains will cease running completely at 6.30pm.

Some operations will be affected from Tuesday evening and disruption could persist into Thursday morning as timetables return to normal.

A nationwide walkout by members of the Associated Society of Locomotive Engineers and Firemen (Aslef), which represents train drivers, is set to close swathes of the network on Saturday. And the Transport Salaried Staffs' Association (TSSA) on Monday called walkouts of thousands of station staff, operational, maintenance, supervisory and management employees at eight companies on Aug 18 and 20, when the RMT also plans to stage further action.

Is the Wednesday strike certain to go ahead?

A Network Rail spokesman said there are no specific negotiations with the RMT planned for Tuesday and that even if a deal was to be reached, staffing for Wednesday is already set - so disruption is inevitable.

Mr Mick Lynch, the union's general secretary, said in a statement that while it continues to talk with employers, "there remains a huge chasm between us".

That is despite an upbeat air around a possible settlement earlier this month, when Network Rail chief negotiator Tim Shoveller said he was "cautiously optimistic" and the RMT promised to present the outcome of "intense discussions" to members. That ultimately led nowhere and the labour group set this week's walkouts in motion.

Which companies are affected?

Workers at Network Rail and most train operating companies will be hit. The latter include long-distance specialists Avanti West Coast and LNER, which link London with Scotland, Great Western Railway, connecting the capital with southwest England and Wales, and nationwide service Cross Country.

The London Underground subway will also be impacted as Network Rail signallers strike on the Tube as well as on surface railways, while TSSA members are staging a separate walkout at Avanti West Coast.

How disruptive is it going to be?

Network Rail says people should "only travel if necessary" and, if so, to carefully plan their trip by checking online beforehand. All major routes will have some services but there will be long gaps between trains and it may be impractical to travel out and back the same day over longer distances.

For example, the last train from London King's Cross to Edinburgh will depart at 2pm, compared with 8.30pm on a normal week day. Tickets will be valid up to Aug 2 for those who choose not to take the risk.

Many people will work from home just as they did during so many weeks of coronavirus lockdowns, but for manual workers, retail employees and other groups that is simply not possible, forcing them to catch a bus, drive or miss a day's work.

With the Aslef strike set for Saturday it is also likely that disruption to normal working patterns may prevail through the end of the week.

What do the strikers want?

Like workers in many other industries, railway personnel are seeking considerable pay hikes to keep pace with the spiralling cost of living.

Britain's trains continued to run throughout the pandemic with government support and companies did not suffer as much as in some other sectors.

A staffing crisis across the economy has given unions a degree of bargaining power, but unlike the airline industry, where demand has surged, the railway is contending what may be a permanent decline in ridership levels as many more people work from home.

For employees, the dispute is as much about job security and working conditions as it is about wages.

Network Rail and the train operators, backed by the government, say pay increases are up for discussion but that they must be accompanied by agreements on modernisation and automation. Working hours, for example, may need to change as fewer people travel in the traditional rush-hour periods.

What's next for the rest of the transport sector?

Airlines, which laid off staff or cut pay during the pandemic, are also contending with strikes this summer.

Deutsche Lufthansa will cancel almost all of its flights from Frankfurt and Munich tomorrow because of a strike by ground crew, with members of the pilot union holding a vote on whether to carry out their own stoppage. Staff at Paris Charles de Gaulle Airport, Heathrow, Ryanair Holdings and EasyJet have also staged walkouts this summer.

SAS reached a deal last week to end a pilots' strike which had lasted 15 days, cost more than US$100 million (S$139 million) and threatened the future of the airline.