A Bus Network for Access Above Demand

Hypothetical King County Metro 24/7 Network map of north Seattle. Route colors are chosen arbitrarily.

This is a hypothetical redesign of King County Metro's transit service in the Seattle area, with smaller changes to Sound Transit service, meant to enhance riders' ability to reach destinations throughout the city whatever the time of day. Within the city's borders, every stop is served by at least one route with 15-minute or better headways, 24 hours per day, seven days per week. This improves riders' ability to move through Seattle by an average of 26.9% on weekdays, with greater increases on weekends.

The resultant network and schedule is viewable in this basic viewer¹.

A Measurement for the Whole City

Access measurements quantify the opportunities available to transit riders within a time budget. Opportunities are destinations with significance to riders. A time budget signifies the maximum amount of time that a person will spend riding, walking, and waiting in a single trip. Calculating an access measurement for a city involves selecting points throughout it and computing isochrones-the region that can be reached within the time budget for a single point-then counting the opportunities within each isochrone. An often-used example of an access measurement is how many jobs the average person can reach within 30 minutes. This is weighted access: the weights are the number of people living around the origin point, and the number of jobs within their isochrome.

Hypothetical King County Metro 24/7 Network map of central Seattle.

However, the analysis in this article uses unweighted access. The access computation simply counts up the origin, destination, and starting time combinations that fit within the time budget. In this case, origins and destinations are sectors of a uniform grid overlapping Seattle. The count of combinations achievable within the time budget divided by the number of combinations, achievable or not, is presented as the Access Ratio. While a higher ratio indicates a greater ability to quickly move through a region, the value itself doesn't map to something intuitive for riders. It is useful, though, as a comparative tool when considering network changes.

While unweighted access may seem like it's discarding relevant information compared to the weighted variant, choosing it for this analysis is intentional. When transit funding is constrained, prioritizing the ability of transit-dependent people to reach vital destinations makes sense. The relative abundance of public transit in Seattle allows the consideration of other goals, like reducing vehicle ownership. With an 80% household car ownership rate, though, a typical person expects to be able to quickly move between arbitrary points in Seattle whatever the time of day. Unweighted access scores public transit's ability to do this.

A Whole New Network

In order to increase the unweighted access score, you'd have to redistribute transit in several ways. Subsequent posts will describe route changes in greater detail. In this analysis and accompanying map:

• Commuter routes are truncated and connected to 1 Line stations.
• Every route within Seattle has a fixed frequency all day, typically no less than its current midday headway.

Headway	Routes
8 minutes	1 Line
10 minutes	RapidRides, 7, 36
12 minutes	6 (portions of 7, 60), 14, 44, 48, 70
15 minutes	All other Seattle routes, except Water Taxi

• Routes that serve stops inside and outside of Seattle are split. The portion within Seattle is rescheduled with a fixed headway. The part outside it maintains its existing schedule, but is not simply truncated at the border. The route is continued to a significant transfer point. The 1 Line, E Line, and H Line are exceptions to this rule; the entire route receives the new span and headway.Here's a list of the new route numbers split from existing Seattle+suburban routes:

New Seattle-Contained Route	Original Seattle+Suburban Route
23	124
35	345
46	106
47	107
51	131
52	132
58	128
72	372

• Some streets that currently have bus service lose it.
• Routes are redesigned, sometimes extensively, to avoid most overlap and create transfer opportunities.
• Streetcars are mothballed.
• Custom Bus" routes for schools (routes in the 980s) and the Water Taxi are unchanged;. Their stops are exceptions to the rule that all stops within Seattle have frequent 24/7 service.

Downtown Seattle is heavily affected by these changes. Buses no longer run on Third Avenue south of Pike Street, or on the Second, Fourth, and Fifth Avenue corridors used by current commuter service. Outside of walking, the 1 Line-running its current peak frequencies day and night-is the sole option for moving northwest-southeast through downtown. In the near future, the 2 Line will supplement it. Routes still cross, or stop at, Third Avenue, providing access to points in the city's east. Routes that once approached from the south are tied into a variety of 1 Line stations. Reaching points to the north and northwest may involve a walk or very short 1 Line trip, then taking route 4, the D Line, or the E Line, before connecting to a route that has been modified to branch off of them. Eastside commuter routes using State Route 520 tie into the 1 Line at University of Washington; those on Interstate 90 connect at Chinatown/International District or Pioneer Square. One-seat rides to downtown would become less common, but with every route contained within Seattle running 15-minute or better headways all the time, transfers are less arduous. Nonetheless, this restructure asks riders to reimagine how they navigate the city.

In return, the access analysis reveals that these changes represent a significant improvement for riders. Metro's last major service change, which expanded service rather than just redistributing it, improved 45-minute access in Seattle by only 1.3%. In contrast, this redesign improves 45-minute access by 26.9%-32.9%, and all time budgets by 16.8%-32.9%.

Schedule	Time Budget	Current Access Ratio	Restructured Access Ratio	Improvement
Weekday	20 min	0.0300	0.0341	13.7%
Weekday	30 min	0.0865	0.1061	22.6%
Weekday	45 min	0.2433	0.3087	26.9%
Saturday	20 min	0.0288	0.0341	18.4%
Saturday	30 min	0.0821	0.1060	29.1%
Saturday	45 min	0.2321	0.3084	32.9%
Sunday	20 min	0.0292	0.0341	16.8%
Sunday	30 min	0.0839	0.1060	26.3%
Sunday	45 min	0.2375	0.3085	29.9%

Excerpt of the map of the change in access ratio for a 45 minute time budget. Red areas are improved under the hypothetical network. Blue areas are better under the present network. The full map is linked in the article.

Each sector has its own access score too, revealing areas of improvement or degradation. This map shows the access change for each sector on a weekday, for three selectable time budgets². For a 45-minute budget, improvement is widespread, with few areas showing modest losses of access. Some streets that have lost service nevertheless exhibit improved access, because nearby routes have increased frequency, span, and transfer opportunities. This even includes Third Avenue, downtown. The 20- and 30-minute time budgets show a more uneven benefit. Areas that have lost their most proximate route more often face an access decrease. Large swaths of improved access remain for these budgets, though, particularly in Metro's Equity Priority Areas, without service investment beyond today's level.

An Unprecedented Shift

Seattle Transit Blog advises contributors that proposals should be somewhat realistic." While this proposal makes sweeping changes to Metro's network, it, critically, requires less in-service time to operate than the present one, on a per-week basis. In-service time tracks with the labor costs that dominate agencies' operating budgets, and is calculable from schedules. It excludes layovers and deadheading, but-by virtue of reducing peak-only service-this network also necessitates fewer deadheads. This property also reduces the maximum number of simultaneously-operating vehicles, permitting a smaller fleet and workforce, or improving reliability with existing resources.

Hypothetical King County Metro 24/7 Network map of south Seattle.

Yet aspects of this network may raise questions about being somewhat realistic." This proposal increases higher-paid overnight shifts. The schedule is also not fully specified: trips have not been collated into blocks and parceled into operator assignments. It may be less conducive to efficient scheduling than the current network. Finally, operators of King County Metro buses, Metro-operated Sound Transit buses, Sound Transit light rail vehicles, and the Seattle Streetcar are considered fungible. All are King County employees, but funding may not be as transferable as this proposal requires.

Reducing peak service also invites concern about crowding. Metro's last two System Evaluations, however, have indicated that its crowding threshold has not been met network-wide, and Metro's crowding definition is conservative. According to New Flyer, a 60-foot Xcelsior coach can hold 61 seated passengers and 62 standees, but Metro considers the same bus crowded if there are on average 83 passengers, or there are more passengers than seats for 20 consecutive minutes. I previously examined Metro's ridership and found that few stop pairs exceeded the manufacturer's capacity of one 60-foot bus running every 15 minutes. The proposed network overlaps routes or increases frequency in these areas. Introducing bi-articulated buses-deployed in European in South American cities-would provide additional relief. There is a greater, and difficult to model, danger of overloading the Link light rail system. This restructure leans heavily on the 1 Line for trips to and through Downtown Seattle. Even with the 2 Line's future capacity infusion, ensuring that future Link vehicle procurements and refurbishments wring as much standing capacity as possible from the vehicle's footprint would help allay the crowding concern.

Perhaps the most unrealistic aspect of this proposal is that it's unprecedented. It doesn't comport with Metro's service guidelines or long-term plans. Planning doctrine positions frequency as a demand-management tool primarily; that it makes transit use more convenient and viable is a consequence, not a motivation. Running service where and when there isn't commensurate present demand is heterodox. There are no examples of a transit agency redistributing resources this extremely.

These unknowns could render this network unrealistic, but whether they are insurmountable is difficult to prove in advance. The proposal's measurable reward does require assuming risk.

Challenging the Status Quo

Transit network redesigns are risky by nature. They never yield universal improvement; this one is no exception. Its tradeoffs are of unusual magnitude, though. The access improvements could be life-changing, particularly for those enduring at-best hourly service where and when they need to travel. Conversely, it subjects riders of some popular routes to longer walks and more-crowded buses. With such polarized outcomes, full implementation of this proposal is unlikely.

As a hypothetical, it is nevertheless useful: it exposes the cost of the status quo. The access increase from completely redesigning Metro's network could have been minimal. This analysis shows that's not the case. While Metro's current choices do benefit riders in ways that unweighted access does not measure, the volume of unrealized access should press Metro to contemplate whether its policies strike the right balance.

A community of transit advocates continually making specific, quantitative appeals to improve access would aid this contemplation. The software used to create and evaluate this proposal is open source and free to deploy.

Footnotes

¹ Due to a data error, the West Seattle Water Taxi appears in the map of 24/7 service. Its schedule is unchanged.

² See also the maps for Saturday and Sunday.