Sydney must decide how much density it can handle, as it plans for 2.4 million extra residents over the next three decades, amid mounting community backlash towards perceived overdevelopment.

Infrastructure Australia, the nation’s independent infrastructure body, on Friday released landmark report proposing three alternative visions of Sydney in 2046, when the population is projected to hit 7.4 million.

The modelling provides a side-by-side comparison of managing Sydney’s rapid growth, either by maintaining the urban sprawl to the city’s fringes, by heavily densifying the inner city suburbs with multi-storey apartment blocks, or by a rebalancing growth across the city in medium density housing.

Under each 30-year scenario, Sydney's infrastructure will be placed under significant pressure, and the average number of hours spent on congested roads during the morning peak will more than double.

Demand for schools will increase by about 70 per cent, while access to hospitals declines under each model. Public parks and open spaces will also become increasingly crowded.