Millions of commuters were facing delays and frustration as a strike by London Underground station staff shuts down much of the city’s subway network. Several central London subway lines were closed during rush hour, forcing many to walk, use overcrowded buses, or work from home if possible. Other Underground lines offered only sporadic service. Drivers on the capital’s roads were experiencing heavy traffic. The strike also closed subway links from terminals 4 and 5 at London Heathrow airport and connections at London’s major train stations. Transport unions are protesting job cuts and ticket-office closures, citing safety issues.