A Tale of Two Buses

Since relocating to Ithaca, I’ve been riding the TCAT bus to work. While my total commute is just under two miles, nearly 300 feet of elevation change make walking less attractive – thus my decision to ride the bus.

Before leaving Savannah, I had also started riding the bus more often. The re-configured dot shuttle to be specific. In September of last year, Chatham Area Transit (CAT) made a major service change on its fare-free downtown routes. For my two mile commute into downtown, this meant public transit was suddenly much more appealing even though I had to walk several blocks to get to the closest stop. (Full disclosure – I worked for CAT while this route change was being considered.)

While these two bus trips might seem similar – they could hardly be more different.

In Ithaca, the Route 14 bus runs once per hour. While I have found it to be reliable over the past couple of weeks, the schedule means I need to plan my travel around its timetable. Thankfully, there is a bus stop relatively close to my origin and destination.

In Savannah, the dot shuttle runs every ten minutes (or six times per hour). I cannot remember ever waiting more than five minutes for the bus to arrive. Most days, I spent more time walking to or from the bus stop than I spent on the bus itself. (The dot shuttle gets a speed boost by operating without fares – this allows passengers to board more quickly.)

Coverage vs. Frequency

These two trips can be thought of along a spectrum of transit service and coverage. On the one hand there is an infrequent trip that covers a large territory. On the other hand is a frequent trip that serves only the most popular destinations.

With a fixed operation cost, this relationship between coverage (distances to the bus stop) and frequency (times between bus trips) can be shown on a graph. As a transit route covers more area, it will run less frequently. Conversely, a transit route that covers less area can run more frequently.


chart showing number of destinations served vs. frequency of service for a transit service with a fixed budget

In Human Transit, Jarrett Walker describes the balance between coverage and frequency as one of the key decisions facing any transit agency. Over decades of rubber tire bus service evolution, many transit agencies have lost sight of this framework as they attempt to use transit for a wide variety of community needs ranging from economic development to social service provider.

In recent years, transit operators have begun formalizing their service allocation policies – in other words they are committing to focus specific portion of their operational budget to offer frequent service and the remainder of their budget to provide coverage to the widest possible geographic area.

how far would you walk for this bus?

I have noticed that I am willing to walk further for a bus that runs more frequently. (While living in Ann Arbor, I trekked nearly a half mile and across a five-lane stroad to ride the Route 4 bus.) In practice, transit planners sometimes build this assumption into their route planning and ridership forecasting. In effect, it means that frequent transit services get a slight bonus in terms of their coverage area because passengers are willing to walk further to the bus stop.

chart showing frequency of service vs. distance passengers will walk to bus stopThis all assumes that a prospective passenger can safely make the journey by foot. Incomplete sidewalk networks, expressways that divide neighborhoods in two, and other physical obstructions to walking often make even short walking trips impossible, unsafe, or undesirable. Regular transit riders need to accurately predict how long their walk to the bus stop will take. Wide intersections that prioritize automobile traffic can make it difficult or impossible for the bus rider to guess how long his walk will take. Unless infrastructure is in place to support walking, there is no reason to assume that people will trek longer distances to reach a more frequent bus service.

What about that bus tracker app?

Sometimes, these important but difficult conversations get off track when a technology vendor offers a novel solution: an app. Proponents of real-time transit data may describe a bus tracker app as a solution to the inconvenience of infrequent bus routes.  The real-time data merely shows the transit rider how to account for delays that are completely outside of her control – like traffic congestion or weather. While there is no doubt that this data is useful, the transit rider is still at the mercy of a schedule that may or may not align with her family or her employer.