Rumi Yoshida manoeuvres her 10-tonne lorry to a halt and leans back in her cabin after nine hours delivering food and drink around Tokyo.
"I like the freedom of this work," says Ms Yoshida, one of 180 drivers at the Shimizu Unyu trucking company. "I don't think it's unsuitable for women . . . My male colleagues don't treat me any differently."
Japan's shrinking workforce, a consequence of one of the world's most rapidly ageing populations, is helping to push a cultural shift in long male-dominated industries such as haulage and construction.
"There were always female applicants in the past but we didn't hire them," says Eiji Shimizu, chief executive of Shimizu Unyu. "There were many applications for our jobs so we had no difficulty hiring staff, and we were afraid that women wouldn't be able to work for long periods because of the nature of the work, which involves handling and loading packages."
But as the number of applicants for its vacancies has dwindled, Shimizu Unyu has opened its doors to women, who now account for 10 per cent of its drivers.
This reflects a national trend. Between January 2007 and October this year, Japan's working-age population declined by 7 per cent to 77.8m, according to government statistics, and job vacancies now outnumber applicants by 10 per cent.
In the increasingly challenging search for labour, companies are turning in growing numbers to women: the proportion of working-age women in employment has risen to record levels, reaching 67 per cent in October.
"Employers no longer have a choice [because of] the tightening labour market," says Atsushi Seike, a labour economics professor at Keio University. "It's really good news — we have wasted a talented female workforce in the past."