Reliability is one of those essential features of transit that you can’t take a picture of. It’s an overwhelming issue in the lives of transit customers but can seem abstract to others who make transit policy. And it’s a major issue in many transit systems.
Poor reliability of buses has many causes, mostly having to do with the traffic congestion and other causes of random delay to which they’re exposed. But when a rail line runs in an exclusive right of way, never interacting with traffic, there aren’t a lot of excuses.
The Miami organization Transit Alliance has done a nice visualization of transit reliability on that city’s rail transit system. It looks at the system right now and shows how many trains are running late. It’s important to note here that late does not mean behind schedule. It means that the maximum wait time is longer than scheduled, by a given number of minutes. (That’s the only rational way to talk about reliability in high-frequency services.)
Some insitute really needs to create a database of reliability info across many agencies, searchable many ways — and always based on this headway reliability rather than on-time performance. Most transit agencies now have real time vehicle location feeds, and they are already released in standard formats for use by apps. Yet we see remarkably few of these kinds of analytics that could help people understand the severity of the reliability problem — even on services like grade-separated heavy rail that have few external causes of delay.