Speed is frequency’s best friend
The “Frequency is Freedom” gospel promoted by Jarrett Walker has quickly spread through the entire public transit industry. His gospel preaches the importance of providing frequent service as a means of “liberating” passengers. Hallelujah.
Frequent transit service reduces wait time, makes transferring easier, and hides reliability problems. More so, the frequency narrative competes with the popular notion that cars are the only mode of freedom. Preaching freedom is much more effective than selling transit on the merits of efficiency, or equity.
I believe in the “Frequency is Freedom” notion, but frequency alone does not make a great transit system. Frequency needs to be accompanied by speed. Speed is the catalyst for achieving frequency.
Why speed matters
“The ability of transit to compete with the car in terms of speed and reliability is critical to attracting ridership, and delay occurs both while buses are in motion – in traffic, from congestion, or at stop lights or signs – and at stops, through unnecessarily long “dwell” times.”
Sustainable Transportation Planning: Tools for Creating Vibrant, Healthy, and Resilient Communities by Jeffrey Tumlin
Speed is important because of what I call the “Three-C’s of faster transit“: Cost, Competitiveness, and Consistency.
- Cost. All else equal, faster transit is cheaper to operate. For example, a 10-mile round trip at 5 mph would take 2 hours, while that same 10-mile trip would only take 1 hour at 10 mph. Doubling speed halves travel time, which halves operating cost.
- Competitiveness. Faster transit erodes the comparative advantage of driving a car and encourages transit usage. Successful public transit systems respect passenger’s time. The best way to achieve that is by ensuring that trips on public transit do not take substantially longer than trips taken by driving a car.
- Consistency. Faster transit is more consistent. Reducing travel time delays not only reduces total travel time, but also reduces the variability in travel times. Smaller variations in travel time means that transit is more consistent and more reliable.
The drudgery of delay
“For urban transit, getting to a destination faster means removing sources of delay rather than raising top travel speeds.”
NACTO’s Transit Street Design Guide
Instead of focusing on increasing vehicle speed directly, it’s better to try to decrease sources of delay. But what are the main sources of transit delay?
Deceleration: Time spent slowing to serve the bus stop
The Transit Capacity and Quality of Service Manual (TCQSM) Chapter 6 – Bus Capacity identifies seven sources of delay associated with bus stops, and provides a range of typical delay durations. I add an eighth component to account for in-motion time.
How to achieve speed?
The Transit Street Design Guide does a great job of prescribing ways to mitigate sources of delay. I created a matrix to summarize the delay reducing potential of each strategy.
If you haven’t done so already, I would highly recommend reading through the Transit Street Design Guide and the Transit Capacity and Quality of Service Manual, which talk about these strategies in more detail. These are two of the most valuable transit operations and planning handbooks out there. They’re essential readings for new transit planners. And they’re available online for free (or use the links above to buy a hardcopy, and help me earn some commission).
In a future post, I plan on elaborating on theses strategies. I’ll also highlight a data-driven approach to prioritizing delay reduction strategies. Here’s a preview of that approach:
