White streamers dangling off trees at some outback rest stops have left travellers unimpressed by such crappy decorations.

As tourists in their caravans head inland and into northern Australia after the heat of summer, a lack of amenities at rest areas prompts criticism.

The problem equally riles some who head south.

"As soon as you cross the border from the Northern Territory into South Australia the availability of toilets doesn't just diminish, it vanishes," said Michael, a Northern Territory traveller.

"As a result, every rest area on the Stuart Highway is littered with toilet paper and other debris, which is not nice.

"Let's face it, when people have got to go, they have to go."

South Australia's director of planning, transport and infrastructure Paul Gelston rejected suggestions there were too few toilets at rest areas.

He said since 2007 in SA there had been 39 new toilets and 37 toilet upgrades for rest areas on major arterial roads, including Dukes Highway, Port Augusta Road, Port Wakefield Road, the Stuart Highway and the South Eastern Freeway.

But he conceded the cost of building and maintaining facilities, the cost of water and fixing vandalism were challenges.

Mr Gelston said simply cleaning the toilets had a significant cost.

One at remote Bon Bon has an annual cleaning bill of more than $17,000 and another public loo at Ranges View cost $11,000 annually.

He said a lack of toilets at some roadside rest stops was also part of a deliberate strategy to encourage travellers to stop in the regional towns.

"We'd always like to put more facilities and more rest stops to encourage people to stop and drive safely, but we have to balance that too with not taking trade away from local towns, local shops and local facilities," he said.

Mr Gelston said funding for toilets had to be balanced against other priorities such as road maintenance works and building new roads.

"Remember that in South Australia we've got a long way between many of our towns. We are not fortunate perhaps to have as many towns located as there might be in Queensland and elsewhere," he said.

Ceduna resident Barbara said people visiting remote areas needed to use their common sense and bury their waste at loo-less stops.

"Everybody has to take some responsibility for the mess at rest stops, take a garden trowel and cover it up. A lot of people complain but they should just do something," she said.

Mr Gelston denied there was any health hazard and urged travellers do their bit to protect the toilets which were on offer.

"That's the point really, asking everyone to treat the facilities that are out there with respect. We'd save so much money if we didn't have to worry about vandalism, for example," he said.