South Australia's transport minister says claims by the opposition that road upgrades in the Adelaide Hills could save residents from bushfires are irresponsible and false.

The opposition has promised that if elected, it would spend $20 million on upgrading traffic infrastructure in the southern foothills to help residents escape from bushfires.

Opposition leader Steven Marshall says the investment would be a “down payment on enhanced bushfire safety” for people living in the area.

The promise comes after a bushfire at Sampson Flat in the Adelaide Hills destroyed 27 homes, injuring dozens of people.

Transport Minister Steven Mullighan says the opposition is simply playing politics ahead of a by-election for the southern foothills electorate of Davenport on January 31.

“It’s irresponsible of a political leader, particularly after what we’ve seen in the last 10 days with the Sampson Flat bushfire, to be peddling a policy which purports to increase bushfire safety for residents,” he told reporters on Monday.

“All the advice from police and emergency services has consistently been to the contrary. Whether a road is one lane in each direction or two lanes in each direction, if a road is impassable due to a bushfire, it’s impassable.”

The Liberals held the seat of Davenport with an eight per cent margin at the March state election.