The move to build a third crossing between Anglesey and the Welsh mainland has taken a major step forward, with the naming of the preferred route.
The so-called 'purple route' over the Menai Strait, was announced by the First Minister Carwyn Jones, and would see a new bridge built to the east of the existing Britannia Bridge.
Facilities for pedestrians and cyclists will also be included.
Mr Jones said construction was due to start in 2021.
The Welsh Government had previously said the new crossing could open in 2021 if it got the go-ahead.
Making the announcement on Anglesey, Mr Jones said he would like the new bridge to be "equally iconic" as the Menai Bridge - built by Thomas Telford in the 1820s - and Robert Stephenson's Britannia Bridge - opened to carry rail traffic in 1850, but rebuilt in the 20th Century to also carry road traffic.
Four option were put out to consultation at the end of last year for bridges east or west of the Britannia Bridge.
Mr Jones said the 'purple route' provided the highest economic benefits and high value for money.
It was also the most popular choice in the public consultation, selected by 25% of respondents as their first choice.
Mr Jones said there was a "very strong case" for increasing capacity across the Menai.
He said: "The A55 is important locally, nationally and internationally. It provides the main economic artery for north Wales and connects the region with the rest of Wales, the UK and Europe.
"The Britannia Bridge is the only section of the route which is single carriageway and we know this reduction in lanes leads to congestion at peak times and during the tourist seasons."
Mr Jones added: "The purple option performs best and would be vital in improving journey times, strengthening the A55's resilience, and ensuring safer travel across the Menai Strait.
"It will also provide economic benefits and ensure the route is fit for purpose as traffic volume is expected to increase over the years to come."
A procurement exercise will now take place to appoint technical advisors to develop the preliminary design.
Economy Secretary Ken Skates said the 'purple route' provided an opportunity to develop a crossing that will allow people to "seamlessly cross the Menai Strait and support future projects such as Wylfa Newydd".
The new nuclear power station will have 8,000 construction workers build it and 850 permanent employees when it starts generating in 2025.
A study was announced in May that will look at whether the third crossing could also carry power cables from Wylfa Newydd.
Mr Skates said: "We fully understand the sensitivity of placing a new crossing over the Menai Strait and further visualisation assessment and analysis work will now take place before the bridge type is selected and taken forward to the next stage of scheme development."
The Welsh Government said the cost of the structure was dependent on this analysis. An earlier estimate of cost was put at £135m.