Peak frequencies hitting limits

Metro systems in Washington, London and Kuala Lumpur are all brushing up against the same limit: once trains are already minutes apart, tiny delays start to spread fast. (wmata.com) (tfl.gov.uk) (myrapid.com.my) The basic measure is headway, the time between trains passing the same point. Shorter headways mean more trains per hour, but they are capped by signalling, station dwell times and how fast trains can reverse at terminals. (wmata.com) (railwaynews.net) (rdso.indianrailways.gov.in) Washington Metropolitan Area Transit Authority’s fiscal 2026 rail plan added “Super Peak” Silver Line trips to raise service in the core to every four minutes for about 40 minutes in the busiest rush-hour period. Four-minute service equals 15 trains an hour; 3.75-minute service would be 16 trains an hour. (wmata.com 1) (wmata.com 2) London Underground’s Victoria line runs far tighter. Transport for London said in a November 4, 2019 timetable change that peak trains would arrive every 100 seconds for about three hours in both the morning and evening peaks, or 36 trains an hour. (tfl.gov.uk) Rapid Kuala Lumpur publishes live peak-frequency updates by line, and its April 2026 morning update listed seven-minute service on the Monorail, four-minute service on the Kajang and Putrajaya Mass Rapid Transit lines, and three-minute service on the Kelana Jaya line. Its older line-frequency page for Light Rail Transit also shows how a five-minute peak can revert to seven minutes outside the busiest windows. (myrapid.com.my 1) (myrapid.com.my 2) The closer a railway gets to those limits, the less slack it has. Washington Metropolitan Area Transit Authority’s core-capacity study said the system, as then equipped, could reliably run a maximum of 26 trains an hour on each track through the core, and lines that share tracks have to split that capacity. (wmata.com) That is why agencies spend heavily on signalling. Transport for London said its Victoria line frequency increase was enabled by a Siemens signalling upgrade completed in 2017, and its separate Four Lines Modernisation program says new signalling will allow up to 32 trains an hour in the central section of the sub-surface network. (tfl.gov.uk 1) (tfl.gov.uk 2) Even with better signalling, the bottleneck can move to platforms and junctions. Washington Metropolitan Area Transit Authority said peak-hour trains are nearing capacity at critical central points on the Red Line and the Blue, Orange and Silver corridor, while Rapid Kuala Lumpur warned on February 26, 2026 that peak-hour crowding was expected at interchange and connecting stations. (wmata.com) (myrapid.com.my) Operators respond with small timetable changes because small changes are often all the infrastructure will allow. In Washington that meant a handful of extra Silver Line rush-hour trips; in London it meant extending the highest-frequency Victoria line service from 90 minutes to three hours; in Kuala Lumpur it means line-by-line frequency adjustments posted as service conditions change. (wmata.com) (tfl.gov.uk) (myrapid.com.my) At these frequencies, “just add more trains” stops being a scheduling question and becomes an infrastructure question. The systems that keep trains safely apart, move passengers on and off platforms, and turn trains around at the ends of lines decide how much room is left. (wmata.com) (tfl.gov.uk) (rdso.indianrailways.gov.in)