Running the Boston Marathon is tough enough without having to jostle your way through some of the route’s famously narrow streets. So this year, organisers have turned to an expert in crowd science to help them manage the field of more than 32,000 as it travels the 26.2 miles (42.195 kilometres) through eight Massachusetts cities and towns. “There are certain things that we can’t change – that we don’t want to change – because they make the Boston Marathon,” said Marcel Altenburg, a senior...