Changes to the roads around the University Hospital of Wales are being introduced in a bid to stop gridlock and help ambulances reach AE quickly.
Hospital bosses hope improving the flow of traffic on the Cardiff site will also stop people being late for appointments.
From Monday, vehicles coming from the Gabalfa entrance to the hospital will be given priority.
It comes after it emerged thousands of drivers use the site as a rat-run.
The new road changes will ensure traffic going past the Emergency Unit will have to give way to oncoming vehicles.
In addition, the entrance at King George V Drive (West) in Heath will have a give-way access to ensure the traffic coming from Gabalfa can flow around the site easily.
Geoff Walsh, director of capital, estates and facilities at Cardiff and Vale University Health Board, said: “The current traffic management system often causes gridlock and significantly decreases the flow of traffic to the site, delays emergency ambulances accessing the Emergency Unit, makes patients late for appointments, staff late for work and, on some occasions, has been unsafe.”
He added: “This will make the site safer and more accessible to those who use it.”
‘Rat-run’
More changes will be brought in from 22 August, when vehicles will not be able to access Gateway Road, the road running next to the Emergency Unit, between 7am and 6pm, Monday to Friday.
In June, a report to the health board said thousands of motorists were using the site as a daily shortcut.
Officials said nearly 8,000 cars appeared to be cutting through the grounds of the hospital every morning, causing “gridlock”, with delays for patients and staff.