Caps on aircraft movements and flight curfews are restricting the efficiency of Sydney airport, according to the Productivity Commission.

A draft report on the economic regulation of airports says these can exacerbate delays, cause congestion and force aircraft to either wait on the ground or in holding patterns in the air.

The report stops short of recommending removing the curfew that applies between 11pm and 6am – an option that would be politically contentious in some marginal electorates.

But it suggests changes could be made to the system that now restricts aircraft movements to 80 an hour, measured over a rolling hour every 15 minutes.

Instead, the commission suggests that either spreading the movement cap over a longer time period than what is now measured, or removing the cap on actual movements but maintaining one on scheduled movements, which “could improve the efficiency of the movement cap without leading to a net increase in noise”.

It also suggests the adoption of noise-based criteria to determine which aircraft can operate during the curfew period, rather than the current system that makes exemptions based on a prescribed list of aircraft types.

The report says the commission “supports the plans for western Sydney airport to operate without a curfew”.

It said Sydney airport’s movement cap, while aimed at restricting noise, could sometimes result in more noise and emissions if planes were “forced to wait in the air rather than land to avoid breaching the movement cap or curfew, creating additional noise, excess environmental emissions and unnecessary fuel burn”.

The draft report still finds that Sydney airport is operating efficiently.

It also finds that the country’s main airports – Sydney, Melbourne, Brisbane and Perth – have not exercised their market power to the detriment of the community.

While many consumers resent the cost of parking at airports, the commission says, high car parking fees were not an example of airports abusing their market power.

“The price of parking at-terminal can largely be explained by the value passengers place on convenience, the limited amount of land close to the terminal, and the need to manage congestion,” the report says.