Some 63 percent of voters accepted the principle of a lake crossing, which aims to relieve traffic congestion through the centre of Geneva and create a full bypass loop.
The text of the initiative did not specify exactly what form that crossing would take, but supporters suggest a three kilometre bridge over the lake linked to a tunnel under the suburbs to connect the motorways either side of the city.
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.
Though now approved in principle, the plan is still a long way from becoming a reality.
How to finance such a crossing – estimated at over three billion francs – is yet to be decided, though supporters suggest a combination of public and private funding.
And despite the favourable outcome of the vote, there is no guarantee that more concrete plans would be accepted in future votes.
The idea of a lake crossing has long been on the agenda in Geneva.
The principle was approved for the first time back in 1988 before voters rejected the idea of a bridge or tunnel in a further referendum eight years later.
Another tunnel project was rejected by voters in 2014.
The Geneva city government supports the plan, with the senate having voted in favour of the proposal in January by 58 votes to 27.