Human frailty has a knack of messing up the finest timetable planning, which explains why buses tend to arrive all at once. "Buses will arrive three at once and every transport specialist knows it," mused Prof Wren, who was marketing his latest program to bus and software companies yesterday.
"Though you can build slack into the system, it's impossible to legislate against a bus or train being late. A few extra minutes on a driver's lunch and everything can change," said Prof Wren, whose interest in transport began as he watched the trams from his grandmother's window in Aberdeen, and continued through four decades of logical analysis.
Leeds bus firm Metro commented: "Blaming the bus company doesn't account for all the things which go wrong on the roads. It's good that somebody realises that."