The average family from western Sydney is paying around $22,000 a year in transport costs, representing as much as 17 per cent of total household income, a new report from a national motoring group finds.

The first national Transport Affordability Index, released by the Australian Automobile Association, whose members include the NRMA, shows a two-car Sydney household faces weekly transport costs of $419 per week.

Sydney households face the highest transport costs of any Australian city both in dollar terms and as a percentage of household income, the report found.

The AAA, which is the peak organisation for Australia's motoring groups and their 8 million members, says it commissioned the report so both consumers and policy makers "have a clear picture of exactly how much transport really costs, and how policy decisions at state and federal levels will affect household budgets over time".