Those in favour of the plan launched their campaign on Tuesday, aiming to show why a road bridge and/or tunnel at the Geneva end of Western Europe's largest lake would ease traffic congestion in the city.
The text of the initiative doesn't specify the nature of the lake crossing, but federal transport authorities suggest a three kilometre bridge over the lake linked to a tunnel under suburban areas that would connect to existing motorways at each end.
The proposal would relieve pressure on the congested town centre and improve conditions for walkers and cyclists, explained city councillor Guillaume Barazzone to news agencies.
According to the text of the initiative, a lake crossing would “reinforce the prosperity of the region and improve quality of life”.
The federal government is already committed to enlarging Geneva's bypass motorway by 2025, to cope with increasing traffic on one of Switzerland's worst bottlenecks.
But supporters say that won't be enough to ease congestion. A lake crossing would create a complete ringroad, they say, allowing drivers to avoid the city centre and therefore reduce traffic by 30 percent.
Building the crossing would also offer the opportunity to develop affected lakeshore areas, reduce noise in urban areas, strengthen the efficiency of public transport, promote walking and cycling, and create new pedestrian zones and public spaces, says the text.
Estimated to cost up to 3.3 billion francs, the crossing could be jointly financed by federal and private funds, say backers.
Other funding models touted include making the crossing a toll road, reported news agencies.
The Geneva city government supports the plan, with the senate having voted in favour of the proposal in January by 58 votes to 27.
The minority felt it could increase traffic and cause damage to the environment and public health.
The plan is also backed by many political parties including the Liberal-Radicals and the right-wing Christian Democrats and Swiss People's Party.
The Socialist Party is against the initiative, mainly for economic reasons. The projected cost of the project is “totally underestimated”, it says on its website, predicting it could be as much as eight billion francs.
The Greens also oppose the idea.
“Genevans do not want to spoil their lake with a bridge that would surely be disgusting,” the Green party's Mathias Buschbeck told the Tribune de Genève last week.
He also doubted the estimated cost and said it would be impossible to finance.
“It would cost 10 to 12.7 billion francs, the equivalent of NASA's space programme to reach Pluto,” he told the paper.