'Why things go wrong'

Why is my bus bunching? Why is my train running express? What is this equipment problem?

The CTA is addressing questions like these in a new post on its Web site called "Why things go wrong." The post, which went live on transitchicago.com Tuesday, tries to answer how delays can occur--though the agency points out that the majority of the 1.7 million rides the CTA provides daily are uneventful.

"This narrative is part of President Forrest Claypool's desire and commitment to better communicate with customers," CTA spokeswoman Tammy Chase told RedEye. "Since his appointment in May 2011, CTA has taken steps to improve communications with our customers during incidents, including more informative platform announcements and expanded use of social media."

The post will not be live updated as a problem occurs, but the CTA does discuss the causes of delays in real-time on its Twitter feed, @CTA.

Some of the topics the post covers:

>> On equipment problems: If there's a problem at a junction (where two or more sets of tracks meet), which could include the loss of signal indications, the CTA may have to manually throw switches to keep trains moving. The agency calls this occurence a rarity.

>> On running a train express: The CTA said sometimes it runs a train express (the train doesn't make all the stops) as a way to relieve congestion after a delay.

The CTA exceeded its monthly target of 78 rail delays of 10 minutes or more for every month last year through November, except for April. There were 102 rail delays of 10 minutes or more in November, according to agency performance metrics.

"Running an express train allows the following trains to pick up more passengers to reduce platform crowding," according to the CTA.

>> On bus bunching: The CTA met its monthly target for bus bunching, when more than one bus arrives at a stop at the same time, from January through August but missed the mark from September through November.

The CTA offers a few theories for bus bunching (car accidents, lane blockage, rider crowding) and a few solutions (scheduling more wiggle room between buses, scheduling more service to reduce crowding).

But the agency acknowledges "corrective actions are complex" and "preventative actions are also not a guarantee."

>> On a bus waiting at a green light: The CTA calls this "running hot." The agency said buses sometimes have to wait at green lights if they're ahead of their schedule so as not to create large gaps of service.

The CTA missed its goals for big gap intervals between buses from May through November but exceeded expectations January through April.