RSPCA Cymru say the announcement is “brilliant news for animal welfare” - and have urged Highways England to ensure similar messages appear in England too
Wales will continue to display messages warning motorists about the dangers of leaving dogs in a hot car during spells of warmer weather.
The Welsh Government confirmed the "brilliant news" in a letter to the RSPCA, who have long championed the benefits the signage can play in raising awareness of their ongoing campaign.
Wales remains the only nation in Great Britain to have taken the step following calls from the animal welfare charity - with the Deputy Minister for Climate Change Lee Waters MS confirming the news.
During spells of hot weather, variable messaging signage on Wales' trunk road network will read: ‘CEIR POETH YN LLADD CWN / DOGS DIE IN HOT CARS’
As lockdown restrictions continue to ease across England and Wales, the RSPCA is determined to spread the message about the risks to dogs of being left in a hot car, as people return to making more regular day-trips with their canine companions.
Dogs left alone in a car on a hot day can quickly become dehydrated, develop heatstroke or even die - but the charity and Police continue to receive numerous reports of dogs left in jeopardy.
When an RSPCA staff member put the rising temperatures to the test, they saw the heat sky-rocket from 23.3°C to more than 57°C degrees in only 26 minutes - highlighting the dangers posed to dogs.
RSPCA campaigns officer Carrie Stones said: "It's brilliant news for animal welfare in Wales that variable messaging signs will continue to share this important campaign message during spells of warm weather - and this remains a first in Great Britain.
"These subtle, awareness-raising messages will save the lives of dogs - by reminding motorists that leaving their canine companions in a hot car can be absolutely fatal.
"If anyone sees a dog in distress in a hot car, they should dial 999 immediately. Sadly, we know too many think it is still acceptable to leave a dog in a warm car - so messaging like this is absolutely invaluable; particularly as Covid restrictions ease and day-trips and travelling become more commonplace again.
"We know temperatures inside a car can sky-rocket in a very short space of time, so it's so important people never leave a dog alone in a warm car. Put simply, not long is too long. We are grateful to the Welsh Government for their support for this campaign in making these road network messages a reality.
"It's hoped Highways England will follow suit - and ensure motorists in England get the same life-saving reminders for dogs when journeying on the motorway and trunk road network there; just like we’ll see again in Wales in 2021."
The Deputy Minister for Climate Change Lee Waters said: "I am very pleased to support this important campaign on our roads. Leaving dogs in vehicles on hot summer days is dangerous as temperatures in cars can rise rapidly even in a short space of time.
“I know the RSPCA and the police receive hundreds of troubling calls about this every year highlighting what a major animal welfare concern this is in Wales so it is crucial we get the message across that you need to think before leaving your dog in a hot car as this could lead to its death."
RSPCA Cymru has campaigned on the issue alongside Newport West's Member of the Senedd Jane Bryant MS, who has also expressed her delight at the news.
Jane Bryant MS said: “It is extremely positive news that Wales continues to lead the way in highlighting this important issue. Dog ownership has increased during the pandemic and for many this will be their first summer as pet owners. ‘Staycations’ and road trips are set to be very popular and so it is crucial that we get the message out there that high temperatures are a huge risk to dogs left in cars.
“I’m very glad that the RSPCA continues to campaign on this issue and I hope that the other UK nations will follow Wales in spreading this important message.”