The A38 St Chad's and Queensway tunnels through Birmingham are now closed - and will stay closed for six weeks until September 2nd.
This is to allow a major refurbishent to the tunnels to be carried out at what is usually the quietest time on the roads, the summer holidays, when traffic levels can fall by as much as one fifth. The whole thing will be repeated next year for six weeks, again starting in July.
The first big tests for the tunnel closures will be the two rush hours on Monday July 22nd. Many road users are predicting traffic chaos - with gridlocked city centre routes.
For one thing, many schools have not yet broken up. And there is likely to be some confusion over how to get from a-to-b, especially for those who have been using the same familiar routes for years.
The tunnels were built more than 40 years ago and have been a useful way of getting across Birmingham city centre. They have been used by roughly 1.5 million vehicles per month.
No-one can be sure what impact the tunnel closures will have at peak times - until it happens. And even then, there are unpredictable happenings like accidents, breakdowns, drivers running out of fuel, plus underground gas and water leaks.
Currently there are Met Office severe weather warnings for the Midlands as humidity rises to 80 per cent and thunderstorms are possible early in the week with the risk of "localised flooding". There are warnings there could be weather-related disruption to transport. Some of the alternative suggested road routes are susceptible to flash flood problems.
These things, of course, may or may not happen. And there may be another unpredictable scenario - the "panic factor". Some people will inevitably choose to stay away from Birmingham city centre, at least at peak times, to see what happens. That could in itself - on Monday at least - actually lead to a fall in traffic. And some commuters may well take heed of advice NOT to drive.
However, the diversion routes in place - and suggested road alternatives - make use of the inner ring road and virtually all other routes in and out of the city, which are already very heavily congested on most weekdays at rush hour.
Amey, Birmingham City Council and Centro have been strongly advising motorists to switch to other forms of transport, or at least to make use of park and ride, including a temporary one which will be free off the A34 at the Birmingham City University campus at Perry Barr. National Express is offering a £3 "tunnel ticket" for a return journey.
Road commuters coming from the south and east of the city can, it is suggested, park at Birmingham International station for "a reduced price" - there are 2,200 car parking spaces there - and catch the train in and out.
Centro has 6,500 free spaces at 57 park and ride car parks at railway stations and near Metro stops (though some of these can already be very busy).
But the main advice being issued is to ditch the car and use buses, trains, the Metro, bicycle, or to walk. Buses are to be given priority in many areas - and there has been a lot of re-organisation of routes and bus stops so bus users should check on how this will effect them. There is information, for instance, on the website: www.networkwestmidlands.com
Birmingham City Council announced recently it will be enforcing bus lanes throughout the city centre with the use of CCTV.
For those who will be driving, signs suggesting alternative routes will be marked with a tunnel icon. The city council says these are "intended to direct people away from potential hotspots and into the city centre via more suitable corridors".
Drivers will find some temporary traffic lights - for example, on the ultra-congested Hagley Road inbound slip road on to Five Ways roundabout, one of Birmingham's most notorious bottlenecks. And there will be traffic lights at the junction where Suffolk Street Queensway joins Paradise Circus.
There will be road closures too - away from the closed tunnels. Most significantly, perhaps, inbound access to Paradise Circus from Broad Street - again, one of Birmingham's busiest routes - will be only for buses, taxis and cyclists. This will be between Bridge Street and Paradise Circus. Broad Street access has been restricted many times in the past, for political party conferences and such like, but never has this been combined with a six-week tunnel closure.
Traffic is to be monitored and, to some extent, controlled from a central control room in the city centre.
The planners say the tunnel closures cannot be avoided - the refurbishment work has to be done. But there are many critics and sceptics. Regular road users say it will make their journeys a nightmare.
Businesses are worried it will lead to staff being late, meetings being disrupted, and trade in the shops, bars and restaurants being hit by visitors avoiding Birmingham altogether. Road haulage, van deliveries, and the emergency services will all feel the impact.
Regular rail and bus users are worried too. Although passengers levels do fall at this time of year, there is still overcrowding at times, and in recent days we have seen delays and cancellations to add to the difficulties.
Commuters complain that even though Birmingham calls itself the second city, it does not (as it did in the past) have the tram network of places like Manchester, or an Underground like London. It was a city re-designed in the 1960s around the car, as the railway system around it was pruned by Dr Beeching. Tram routes have been talked about for decades but so far only one has been built.
You can find further advice and interviews about the tunnel closures on our website. We will also be keeping you up-to-date here as things progress and, of course, on the ITV News Central bulletins and programmes.