A study on the environmental impact of the national exhibition in 2002 has criticised transport policy, describing it as the "weak point" of the project. However, it adds that viewed as a whole, the exhibition plans to respect the environment.
The exhibition - Expo.02 - is due to take place around the lakes of Biel, Neuchâtel and Murten.
In its third independent report on environmental controlling, the Aquarius company of Neuchâtel says there is a need for a rapid solution to the issue of pricing policy.
"The fixing of fees which are really attractive and encourage public transport is bogged down. The concept of parking near the exhibition sites taking into consideration those who will park their cars illegally is judged insufficient at present," the study says.
It adds that transport is all the more important because it alone would account for 60 to 70 per cent of potential harm to the environment.
Organisers say that they agree with the study when it comes to offering attractive prices but are having second thoughts about a one-price structure which had been proposed and supported in the two previous environmental studies.
"How can you expect someone from Biel who goes to the exhibition on foot or by bicycle to have to pay the same price as someone who travels from the other end of Switzerland?" asked Jacques Soguel from the Expo management.
He said that plans were being examined to combine transport and entry fee with a reduction, a practice which is pursued for several fairs at Geneva's Palexpo exhibition centre. The price would be variable and depend on distance and the mode of transport used.
The study also criticised the staff transport policy. It says that the 9,000 people employed during the exhibition will be ferried to and from the sites by public transport. The aim is praised, but Aquarius says materialisation of the aim is "non-existent".
swissinfo with agencies