Driving hard

TRAVIS KALANICK, Uber’s hard-nosed chief executive, seems to relish taking on regulators and rivals. “I realise I can come across as a somewhat fierce advocate for Uber,” Mr Kalanick recently quipped at a celebration for the taxi-hailing company’s fifth birthday. “I also realise some people have used a different ‘a’-word to describe me.” Mr Kalanick’s brashness has helped Uber become the most valuable American company of its generation. If it succeeds in raising a further $1.5 billion from investors, as reports indicate, its implied valuation will soar to a staggering $50 billion. That is higher than 80% of the firms in the S&P 500 index, many of which are decades old. Uber’s value has grown faster than those of Facebook and Twitter in their early years (see chart).