When considering the environmental damage caused by road traffic, one traditionally focuses attention on the consequences of accidents, or on the impact of air and noise pollution. This somewhat narrow definition should be enlarged to capture other, more psychological nuisances. The barrier effect created by heavily travelled streets belongs to this group of nuisances, rarely described and never estimated in monetary terms. It particularly affects children, the disabled and elderly people for whom the street becomes too large to cross. In a survey carried out at Neuchâtel, Switzerland, a contingent market was proposed to suppress the barrier effect around the city centre. A valuation function to predict the bids is estimated and used to infer the annual cost of the nuisance.