One of the most visible causes of bus delay is "dwell time" at stations, the amount of time buses spend waiting for passengers to enter and exit. For example, a 2002 Schaller Consulting report examined the M15 bus in New York City and observed dwell times of up to 1 minute 45 seconds in crowded conditions, and of more than 4 minutes during use of the wheelchair lift. Las Vegas-area buses sometimes suffer dwell times of up to 5 minutes at crowded stops.

The main cause of dwell time delay is the bottleneck caused at the onboard farebox: When many riders need to board, delays occur - and are exacerbated when riders can't find change, don't know how to use fare media, etc. Delay also occurs when passengers are squished into too few doors, or if exiting passengers use the same door as entering passengers. Finally, in high-floor bus models, the need to negotiate stairs can cause problems for the mobility-impaired and cause further delays.

At left, Boston bus riders wait to pay their fares. (Photo: Mika Tomczak/MIT).