Hospital bosses made changes last August in a bid to help ambulances reach the emergency unit more quickly at the University Hospital of Wales (UHW) in Cardiff.
Barriers were installed and traffic is not allowed to drive past the unit.
The gridlock also led to people being late for appointments.
Cardiff and Vale University Health Board is now planning to introduce a direct weekday park and ride service for patients, visitors and staff in a further bid to keep traffic off site.
It will start on 2 May and operate from Cardiff East park and ride at Pentwyn from 06:30 to 19:15, running every 20 minutes, which should also free up car parking by 12%.
There are also plans to introduce bus and cycle hubs at UHW.
Geoff Walsh, director of capital, estates and facilities at Cardiff and Vale University Health Board, said: "The traffic management system was implemented to allow clear access for emergency vehicles onto the site which has been successful.
"It has also improved the bus access with Cardiff Bus reinstating two services following the improvement of site accessibility."
He added: "We are still looking at ways to stop people using the site as a thoroughfare."

The 25-year-old striker has played for three promotion-winning Championship sides in four seasons, at Hamilton, Hearts and Hibs.
United face Morton in the Premiership play-off quarter-final first leg at Cappielow on Tuesday, 9 May.
"I am joining a fantastic club with a great reputation who are set up to be in the Premiership," Keatings said.
"I look forward to joining Dundee United. I have enjoyed playing at Tannadice, and my goal is to be scoring in the Premiership for United whether it is next season or beyond."
Keatings made 30 appearances for Championship winners Hibs this season, scoring eight goals.

Fly-half Sexton and flanker O'Brien have both recovered from calf injuries and should be available at Murrayfield.
Sexton was injured against Castres on 20 January but is said to be "feeling very positive" about his recovery.
However, uncapped Munster wing Andrew Conway has been ruled out after aggravating an existing groin problem.
Ireland playmaker Sexton has the chance to cement his starting spot, provided he comes through Tuesday's session.
Ulster's Paddy Jackson will start for Joe Schmidt's side if the Leinster star is ruled out while Munster's Ian Keatley has joined the squad as cover for the time being.
"Johnny's making good progress and he's back on track to train on Tuesday," said Ireland team manager Paul Dean.
"I think everything is fine, he's being very positive about it."
O'Brien has completed the rehabilitation on his calf issue and was expected to take full part in Monday afternoon's training session.
Full-back Rob Kearney says Ireland remain unfazed by his Leinster team-mate Sexton's latest quest for full fitness.
Sexton battled hamstring trouble before the turn of the year, with this calf problem proving yet another unwanted hurdle.
Kearney labelled injury doubts "par for the course" in any Test week, then tipped Sexton's understudy Jackson to thrive if pressed into service from the start in Scotland.
"We're all so used to it now," said Kearney, of general battles for fitness.
"On a weekly basis, more often than not, there's someone going in or out.
"Someone picks up a niggle or they're not fully fit, so the coach doesn't risk them. The way Test rugby is now, it's par for the course.
"Paddy [Jackson] has been there all last week running the plays. He's more than equipped and he's got a week head-start."

The former Chesterfield first team coach replaced Ashley Hoskin as manager in October 2015.
But the Seagulls managed four league wins under Lynch and are nine points from safety with eight games remaining.
"We thought he was the man for the job but unfortunately it didn't work out," Bay chairman Dave Titchiner said.
Captain Carl Rodgers and Luke Denson will be in charge for Thursday's home game against Mickleover Sports.
Colwyn Bay were relegated from the Conference North at the end of the 2014-15 season.
The amount of traffic using Wales' biggest hospital as a "rat run" and causing gridlock has dropped by 7% after changes were made to the roads.
[NEXT_CONCEPT]
Hibernian striker James Keatings has signed a pre-contract agreement with Dundee United.
[NEXT_CONCEPT]
Ireland pair Jonathan Sexton and Sean O'Brien are set to resume full training after injury before Saturday's Six Nations opener against Scotland.
[NEXT_CONCEPT]
Evo-Stik Northern Premier Division strugglers Colwyn Bay have sacked manager Kevin Lynch following Easter Monday's 3-0 home defeat to Marine.