Sioux City: Straightening Buses and Getting Route-Length Right

A few days ago, Sandy Johnston linked to a diagram of the single bus route in South Sioux City, Nebraska, a suburb of Sioux City, Iowa. While South Sioux City has a traditional main street in Dakota Avenue, the bus does not follow it; it meanders, hitting destinations on and off Dakota. Many destinations are on US Route 77, an arterial bypass around the built-up area, with recent auto-oriented retail and office uses, including a Wal-Mart (in small-town America often the biggest bus trip generator). The discussion around what to do with this region’s bus network made me realize a crucial concept in planning infrequent transit: getting route-length right. To start with, here is a map of the bus, numbered Route 9 within the Sioux City area:

Here is a PDF map of the entire network. It has 10 routes, using 12 buses running hourly, with a timed meet at the center of Sioux City (just off the above map) at :30 every hour. Most routes run as loops, with highly separated inbound and outbound legs. Route 9 above runs one-way southbound on Dakota Avenue in the northern and southern legs but then meanders to run southbound on Route 77; the Dakota Avenue leg in between the two major east-west runs is one-way northbound.

I asked, why need it be so complicated? The major destinations are all on Dakota or Route 77. It should be easy to run two distinct routes, one on each, right? Without the east-west meanders, there would be the same total service-hours, right?

But no. The route runs hourly. The scale of the map is small: from the bridge over the Missouri in the north to I-129 in the south it’s 4.1 km. There is so little traffic that in the evening rush Google Maps said it would be just 10 minutes by car from Downtown Sioux City to the southern edge of Dakota Avenue near I-129. The roundtrip time would be 25-30 minutes, so the bus would sit idle half the time due to the hourly pulse.

Getting route-length right

When designing regional rail schedules, as well as my take on night buses in Boston (since reduced to a single meandering route), I’ve taken great care to deal with roundtrip route length not always being an integer multiple of the headway. A train that comes every half hour had better have a roundtrip length that’s just less than an integer or half-integer number of hours, counting turnaround times, to minimize the time the train sits at the terminal rather than driving in revenue service. The same is true of buses, except that scheduling is less precise.

In Boston, the plan at the time was for hourly buses, and has since changed to half-hourly, but the principle remains. The roundtrip length of each leg of the night bus network, should it expand beyond one (double-ended) route, should be an integer or half-integer number of hours. In practice this means a one-way trip time of about 25-26 minutes, allowing for a little recovery time and for delays for passengers getting on or off; overnight there is no traffic and little ridership, so 25 minutes of driving time correspond to just less than 30 minutes of actual time.

Thus, on each corridor, the bus should extend about 25 minutes of one-way nighttime driving time from the connection point, and the choice of which routes to serve and where to end each route should be based on this schedule. Of course on some shorter routes 12 minutes (for a half-hour roundtrip) and on some long routes 38 minutes (for a 90-minute roundtrip) are feasible with half-hourly frequencies, but in Boston’s case the strong night bus routes in practice would all be 25.

Length and frequency

In the case of Sioux City, hourly buses meeting at the center should have a one-way trip time of 25 minutes. However, the city is so lightly populated that there is little traffic, and the average traffic speed is so high that 25 minutes puts one well outside the built-up area. The driving time from city center to the edge of the built-up area, around I-129, Lakefront Shopping Center, and the various Wal-Marts ringing the city, is around 10 minutes.

Moreover, a car travel time of 10 minutes corresponds to not much longer on a bus. Frequent commenter Zmapper notes that in small American cities, taking the driving time in traffic and multiplying by 1.2, or 1.3 with recovery time, is enough. A one-way driving time of 11-12 minutes involves a roundtrip bus time of half an hour.

With such a small urban extent, then, the bus frequency should be bumped to a bus every half hour, leveraging the fact that few important destinations lie more than 11-12 minutes outside city center. The question is then how to restructure the network to allow for doubling frequency without doubling operating expenses.

The importance of straight routes

Some of Sioux City’s bus routes go beyond the 12-minute limits, such as route 6 to the airport. But most stay within that limit, they’re just incredibly circuitous. Look at the map of route 9 again. It jumps between two main corridors, has multiple loops, and enters the parking lots of the Wal-Mart and other destinations on US 77.

The reason for the meanders is understandable. US 77 is a divided highway without sidewalks or crosswalks, and none of the destinations thereon fronts the road itself. From the wrong side of the road to Wal-Mart it’s 330 meters, and a few other retail locations are more than 100 meters off. Many agencies wince at making passengers walk this long.

However, understandable does not mean justifiable. Traversing even 330 meters takes only about 4 minutes, and even with a hefty walking penalty it’s much less than the inconvenience caused by hourly headways. The other routes in the Sioux City area have the same problem: not a single one runs straight between city center and its outer destination.

With straighter routes, the savings in service-hours would permit running every half hour. A single bus could run every half hour if the one-way car travel time were at most 11-12 minutes; up to 23 minutes, two buses would provide half-hourly service. With 12 buses, there is room to replace route 9 with two routes, one on Dakota and one on US 77 (possibly entering the Wal-Mart, since the route is so short it may be able to get closer to Wal-Mart while still staying under 12 minutes). The Lakeport Commons and Southern Hills Mall area could get buses at the entrance, as it is the logical end of the line (route 1, to Southern Hills).

Some pruning would still be required. Some low-density areas far from the main corridors would have to be stranded. Some circumferential lines would be pruned as well, such as route 10 (to the Commons) on US 75 and route 2 (on Pierce Jackson) to Wal-Mart. Circumferential lines at such a low frequency are not useful unless the transfers to the spokes are timed, which is impossible without breaking the city center interchange since the lines take different amounts of time to get between city center with the plausible connection point. Ultimately, replacing the hourly routes with half-hourly routes would guarantee better service to everyone who’d still get any service, which is nearly everyone.

It’s not just Sioux City

I focus on Sioux City because it’s a good toy model, at such scale that I could redesign the buses in maybe two weeks of part-time work. But it’s not the only place where I’ve seen needlessly circuitous routes wreck what should be a decent bus network for the city’s size and density. In 2014 Sandy wrote about the bus network in New Haven, which has okay trunks (I only needed to hitchhike because of a bus delay once – the other four or five times I took the bus it was fine) but splits into indescribably complex branches near its outer ends.

More recently, I looked at the network in Ann Arbor, partly out of prurient interest, partly out of having gone to two math conferences there and had to commute from the hotel to the university on the city’s most frequent bus, route 4. Zoomed out, the Ann Arbor map looks almost reasonable (though not quite – look at routes 5 and 6), but the downtown inset shows how route 4 reverse-branches. Ann Arbor is a car-oriented city; at my last math conference, in Basel, a professor complained that despite the city’s leftist politics, people at the math department were puzzled when the professor biked to campus. The buses are designed to hit every destination someone who’s too poor to own a car might go to, with speed, frequency, and reliability not the main concerns.

The underlying structure of bus networks in small American cities – radial buses converging on city center, often with a timed transfer – is solid. The problem is that the buses run every hour when cities should make an effort to run them every half hour, and the routes themselves are circuitous. In very small cities like Sioux City, increasing the base frequency is especially urgent, since their built-up extent is so compact a direct bus would reach the limit of the serviceable area in 10-12 minutes, perfect for a half-hourly schedule, and not the 25 minutes more typical of hourly schedules. Sometimes, scaling down requires maintaining higher frequency than the bare minimum, to avoid wasting drivers’ time with low-value meanders.

28 comments

  1. Bjorn

    Slight correction: Base service is ran with ten (10) buses, not 12. I hurriedly thought that there were twelve routes when responding on Twitter. (The S. Sioux City bus used to be Route #12.) https://www.sioux-city.org/government/departments-q-to-z/transit/service-changes

    During peak hours when the public schools are in session, the peak vehicle requirement is 17; seven buses run special routes nominally open to the public and are used in lieu of school buses. For some reason, a few main routes truncate at bell times to avoid travelling near the school campuses.

    • Alon Levy

      It’s possible to run half-hourly service with ten routes too, but with more painful compromises on coverage. On Twitter the twelve routes I proposed assumed the North Sioux City route would be run with two vehicles, but it’s possible to run it with one if you’re okay turning at city hall and not deeper into North Sioux City. That gets you down to 11. To get to 10 there are a few options, none great – consolidate the eastern routes to two, only run one route in South Sioux City (either on Dakota or as a Dakota/77 compromise terminating at Wal-Mart), or cut the Floyd Boulevard route and run the Jackson/Pierce route to Wal-Mart instead.

      And why do buses avoid traveling near schools?

      • Eric

        Possibly the crowd of students would disrupt the route timings too much, so students are made to take special student buses.

        • Alon Levy

          That still seems inefficient. They could let students ride for free (e.g. not charge fares at school stops at school leaving times) – the farebox recovery ratio is low enough that the hit to revenue is much less than the extra operating cost from extra buses. Then, since it’s a one-time disruption to the schedule, it’s okay if the bus is delayed by a few minutes on one trip because it can make it up on subsequent runs.

          Relatedly, ant6n argues in favor of very little recovery time scheduled on night buses, because the night bus network only lasts 4-5 hours, so there’s not enough time for routine delays to wreck the schedule (on a half-hourly system nobody cares about sub-5 minute delays).

  2. red dog

    I’d like to see ridership totals for Sioux City. I’m guessing that most buses run at maybe 20% of capacity; is the thought that half-hourly service would greatly increase ridership? Unless the fare box covered the additional costs that come with half-hourly service, which is highly doubtful, how would these costs be met? (costs such as fuel and wear and tear on the rolling stock) Realizing that balancing the various factors effecting ridership is a highly localized process, factors I’m not party to, I can’t imagine asking shoppers to carry purchases through parking lots to remote stops on highways that usually aren’t friendly to foot traffic is going to be an effective policy to increase ridership

    • Alon Levy

      I don’t think there would be extra fuel costs – I’m proposing using the same amount of service-hours to run straighter routes. To the extent it involves higher average speed and more service-km, it comes from making fewer meanders through parking lots, which means more driving in highway or near-highway conditions and fewer acceleration-deceleration cycles.

      The buses are empty (they average 8 people per bus), but when routes run hourly, you get into a frequency-ridership spiral, in which low frequency and low ridership reinforce each other. It’s not like when discussing whether to run a bus every 3 minutes or every 5, where frequency itself has no effect on ridership.

      • red dog

        Agreed, the secret is finding the balance, the sweet spot between frequency and the quality of stops. So, what’s your best guess as to what running the system at half-hour heads would do to off peak ridership? Would a 20% increase year over year be ‘enough’?

      • adirondacker12800

        It’s not serving a market of healthy people in one car instead of two car households. It’s serving a market of people so disabled they can’t drive and diverting off to the entrance of the store is the service they want because they can’t walk across the parking lot. Too poor or too disabled or both to have a car with a handicapped parking space permit. And probably the places that don’t qualify for medical transport from Medicaid/Medicare. The person or people who are co-coordinating medical transport would be the ones to talk to about what is going on. It’s scheduled shared ride instead of on-demand.

  3. Diego Beghin

    I was at a conference in Virginia Tech – Blacksburg recently, and I was quite impressed* by the transit system there. 4-5 bus lines converge on a 30-min pulse in front of the university. The bus rode the 3 km** from the campus stop to my hotel in 6 min, so that’s a 30 km/h commercial speed. The buses were reasonably full (of students). It’s best practices small town transit, better than many towns of the same size over here.

    I wonder if college towns in the US are generally better-than-average at transit?

    *My expectations were very low to be honest.
    **3 km is just close enough that half of the time walking was still faster. But I took the bus a few times.

  4. hotsaucephd

    To what extent are the meandering routes simply an alternative (if perhaps suboptimal) strategy to cope with the high avg. traffic speed? “If I have to slow down, I might as well veer off course and pick up folks in adjacent areas.” They spend the inefficiency with respect to the direct route on “access/service” to the adjacent areas. Maybe?

    • Alon Levy

      I can sort of see why they’d think this way on sidewalk-free near-expressways like US 77, but then why the meanders on Dakota or the Indian Hills route, or the loop on the Council Oaks route?

  5. ckrueger99

    See New Jersey Transit’s bus network in South Jersey/Camden, a hemisphere focusing on WRTC/Broadway in Camden near the main bridge to Philadelphia. Great coverage but with meandering all over the place. Terrible headways. Very little attempt at mode share with the PATCO subway/el that goes over the bridge, particularly with fare payment, to say nothing of that with SEPTA in Philly itself.

    • red dog

      This is a different story, but NJ and PA need to find a way for SEPTA to take over and integrate into their system, the PATCO trains. As the Delaware River Port Authority has shown no great interest is running a one line system.

      • adirondacker12800

        and NJtransit should be intergrated with the MTA and keep this up, everything between Montreal, Portland Maine and Richmond Virgina is all one big blob. And people are whining about why isn’t their transit pass good in Tokyo and Paris. There’s gotta be borders somewhere. The Delaware and the Hudson are really good ones.

      • Eric

        Last I checked PATCO runs its line pretty well, while SEPTA gets a lot of criticism. So don’t fix what isn’t broken. That said, fares should be integrated of course.

        • Jacob Manaker

          Actually, the larger problem is that the Atlantic City Line is perfectly set up to run as Lindenwold-Haddonfield expresses, but can’t without fare integration (and maybe higher frequencies). You’ll note that the current schedule lists times via PATCO to Center City, so it’s not like they don’t expect passengers to transfer. (Along the same lines, the ACL should probably stop at North Philadelphia station.)

          • adirondacker12800

            Stop at North Philadelphia so they have more time to watch the deserted platform in the hope of seeing one of the very rare users of North Philadelphia?
            PATCO is third rail, the Atlantic City line is not grade separated. It would be difficult to get approval to install third rail. The Atlantic City line is dead straight with few stations. Perfect for higher speed. Third rail has trouble with high speeds.

          • Alon Levy

            In London trains go 160 km/h under third rail, though they lose 25% of power consumption to heat; Network Rail says they’re only good up to 80 mph. But 80 mph is the maximum speed of the Atlantic City Line, so third rail should be fine there if it’s not possible to use dual-voltage trains on PATCO.

          • adirondacker12800

            It straight and flat and they don’t want to spend money for more than class 4 track for 2,000 passengers a day. Or electrifying it. There’s lots of other places in New Jersey where electrification money would be better spent. The reason it’s a train is to stop southern New Jerseyans from whining about how Northern New Jersey isn’t wasting enough money on them.

          • ckrueger99

            Agree that both AC and Riverline created for political reasons, to make southjerseyans feel some love from Trenton. Let’s assume that the money available is fixed: how do we spend it more wisely? Expand the DMUs from Riverline to AC line higher frequency Lindenwold to AC, develop the Glassboro line to connect with the RiverLine at Broadway for small bucks. Reorganize the SJ NJT bus network mentioned above.

          • adirondacker12800

            A nicety would be to use an ALP45 instead of straight diesel. No fumes in 30th Street. Beyond that they should be grateful it’s not a bus to Lindenwold. The proposal back in the 60s was for Glassboro and Trenton to be branches of what is now PATCO. Double tracking will cause the fabric of the universe to rend, turn Cinnaminson into Jackson Heights and Gloucester City into East New York. They can take the bus. As a former resident of Northern New Jersey who had to deal with complex zone and transfer structures I’d love to get 30 mile rides for one zone.

  6. Bjorn

    This problem is encountered when the cycle length takes less time than the desired headway. In Iowa City, most routes run every hour off-peak, yet the city is compact enough that nearly all routes either take 30 or 45 minutes to cycle out and back from the Downtown Interchange. The city’s transit system interlines two routes with a 45-minute cycle and one route with a 30-minute cycle, to create a master route with a 2 hour cycle. As an example, the Court Hill route becomes the Lakeside route, which becomes the Westwinds route, which becomes the Court Hill route when it arrives back Downtown. In turn, if routes don’t have a common cycle length (or whole-number multiple), departure times have to be offset. This isn’t entirely a problem, as two routes can be overlaid in areas to boost frequency (the Court Hill route shares a common segment with another route which departs at the :00 and :30).

  7. Nicolas Centa

    If the target is to serve people too poor to own a car, and also disabled people who may not be able to drive one, isn’t coverage more important than anything else?

    It is not the same as a bus network whose goal is to decrease car use as much as can be done with given resources.

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