Drivers expecting smooth flow through the Tyne Tunnel on Monday have been put on red alert – due to a new traffic light trial.
For the next fortnight, the rarely used lights at the south side entrance will be turned on full-time.
Tunnel bosses say the measure is only temporary to check if a new and better traffic management system is possible.
They insist it has come in response to dialogue with drivers who raised concerns about difficulties filtering onto the A19.
But they admit it could become a permanent option if it is shown to improve journey times.
Phil Smith, chief executive of TT2 Ltd, which operates the tunnel, promised the test would not add to congestion - and would be quickly halted if it did.
Defending the move, he said: “One of the common themes is about congestion at the junction immediately south of the tunnel.
“If you’re coming from South Tyneside, you’ll be aware of the difficulties there is with traffic merging.
“What we want to do is understand what the driver behaviours are, how people are merging and what we can do to try to improve that.
“It’s not going to lead to more hold ups because the entire purpose is to understand how to reduce them, so if we were doing something that would make matters worse we would stop them.
“The purpose of the temporary lights is that it gives us immediate control, so if we see that things aren’t as we would want them to be, if the trial plan isn’t working, we can suspend straight away.”
Mr Smith said the trial had been planned to coincide with the summer holidays when there was lighter traffic load.
And he confirmed various scenarios would be tried and tested during the fortnight to check if roads management could be improved.
He added: “From my own point of view, any delay is a bad delay. We have to bear in mind that traffic is increasing year-on-year and we want to try to prepare for the future.
“Some of the thoughts we’ve had might be very long-term, some might be a bit quicker, but we need to start that conversation now.”
The lights trial will end on Monday, August 27.
The original single lane Tyne Tunnel was opened by the Queen in 1967.
The £260m second Tyne Tunnel, which opened in November 2011, is used by around 50,000 vehicles a day.