Trip Chaining, Redux

There’s been an ongoing conversation about how public transport can be used for non-work trips (and what it means for women) that makes me go back to something I wrote in 2012 about trip chaining. In that post I asserted a distinction between long and short trips, but I didn’t make it very clear. The importance of this distinction is that even though a large majority of trips are not work trips, the sort of urban layout that makes long trips (including work trips) usable by train tends to also make other trips doable on foot.

Trip length and purpose

Mobilität in Deutschland periodically reports on national travel patterns. The 2017 MiD report includes mode shares, trip lengths, and purposes, some broken down by state. Unlike in the Anglosphere or in France, the headline modal share is for all trips, not just work or school trips, and therefore the numbers for public transit look lower and those for walking and cycling look higher.

The important statistic for trip-chaining comes from a table on p. 19. There were 42 million work trips and 41 million shopping trips nationwide in 2017, but the work trips were on average more than three times as long, 16 vs. 5.3 kilometers. The only trip category longer than work was business trips, on average 19 km, including an extensive number of intercity trips, and the only category close to work trips was recreational trips, averaging 15.5 km, also including extensive intercity travel; the median work trip was by a fair margin the longest, 8 km, whereas the median shopping trip was 2 km. Likewise, errand trips were 10.2 km on average with a median of 3.6.

MiD doesn’t break down this data by region, unfortunately. So I can only speculate that if the median trip that people talk about when they talk about trip chaining is 2 km long, then the median trip in the parts of Germany with good public transit is short enough to be done on foot, probably shorter than a kilometer.

Short and long trips

I think it’s useful to collapse the distinction between trips into a binary one: short versus long. Trip length is of course a continuous variable, but a good classification scheme is “can it be done internally to a neighborhood or town?”. If the answer is yes then the trip is short, otherwise it is long.

The commute is an example of a long trip. Commuting to school is usually a long trip as well; even in an environment with school zoning and no selection or choice, a secondary school draws from too large an area to be a single neighborhood except in an extremely large and dense city. Social trips can be long as well – if I go to a gaming convention or a performance in Berlin, or if someone who cares about sports goes to see a football match, it’s a long trip.

Short trips include shopping, errands, eating out, and daycare. The common aspect to them is that they involve common activities with small draws. The supermarket draws from a community of a few thousand, as does the neighborhood restaurant. In contrast, the performance is unique – while many people go to concerts, different people are fans of different artists, so a single band may need to visit a city of millions to fill an auditorium.

Making transit useful for non-work long trips

I bring up the example of going to a sports game as a long trip because American transit agencies deal with that routinely even if they otherwise only care about work trips. Commute trips tend to happen at specific times of day, especially if you’re from the same middle class that transit managers are drawn from. Other long trips have different peaks. Leisure trips tend to happen in the evening and on weekends. Business trips within metropolitan areas tend to happen in the middle of the day during work hours. Trips to the airport depend on time zones – in New York the ones to JFK are concentrated in the afternoon peak, but it’s hard to make generalizations.

Like work trips, non-work long trips are not isotropic – people travel to specific places. A few are as a rule outside city center, such as sports stadiums and airports. Others are within city center to appeal to a wide cross-section of residents, such as event spaces for performances; conventions run the gamut, but richer and more important conventions are likelier to shell out money for city center real estate. Universities may be in or outside city center, depending on the city. Museums are usually city center or in neighborhoods just outside it, such as the Upper East and West Sides in New York or Balboa Park in San Diego.

The length means that the optimal transit network for all non-work trips is largely the same. If trains arrive at a reasonable frequency all day, every day, and form a coherent radial network, then passengers will able to use them for all long trips, even ones that are not for work. The major destinations that are outside city center should whenever possible be junctions between different branches, or get circumferential and not just radial service.

Moreover, there is little point in trying to vary modes for work and non-work trips. Surface transit that averages 15 km/h but saves you a 1-minute trip down to the subway is no more useful for going to a concert than for going to work. If poor urban planning has resulted in an airport that’s nowhere on the rail network or in regional convention centers that are impossible to serve, then buses can fill in the gap, but that’s not optimizing for non-work trips but rather fixing past design mistakes, no different from doing the same when suburban office parks are built far from the train.

The one serious change one needs to make is that the definition of city center needs to be broader than the few square blocks that comprise most American cities’ downtowns. The London Underground’s conception of Central London is not just the City, and likewise cities need to ensure that their West Ends (like, again, San Diego’s Balboa Park) are served as if they were central rather than peripheral areas.

Short trips

It is wrong for cities to try optimizing public transportation for short trips. Most short trips can be done by foot; if they can’t, something is wrong with the city’s urban design. The minimum density required for people to be able to walk to retail is not high – I have a choice of supermarkets within walking distance, and Berlin is not an especially dense city. In Paris, which unlike Berlin is especially dense, I walked to the hypermarket.

Occasionally, when a short trip needs to be done on mechanized transportation, if the city has good transit-oriented commercial development then it is doable by riding the trains a few stops. I recently bought a mattress at Hermannplatz, 3 stops away on U7, longer than most people inside the Ring have to go to such a store, and mattresses are a special case in that dragging them on the streets for a kilometer isn’t fun.

Suppression of auto use is especially valuable for short trips. The reason is that in auto-oriented areas, short as well as long trips are done by car, and if businesses locate based on automobile scale, then only transit can compete – walking and cycling take too long. A hefty proportion of the urban upper middle class prefers to own cars and drive them for short trips, which may induce short trip destinations to locate based on automobile scale even in a walkable city; when I lived in Providence, I walked to the supermarket, but it was located right next to a freeway exit and had ample parking.

Trip chaining

The concept of trip chaining – going directly between destinations in a row rather than just going back and forth between home and a destination – works best with the mode of transportation with the highest frequency and lowest access time: walking. Buying different items at different stores is so ubiquitous that shopping malls were invented specifically to make that experience more pleasant than that of chaining car trips.

Transit cities should not design themselves around trip chaining on transit, destinations for short trips are too difficult to serve. Many cluster on major corridors, but some don’t and stay on residential streets or at street corners. In walkable cities they tend to be fairly isotropic. With short average trips and no discernable centers, the optimal stop spacing on transit is extremely short, to the point of uselessness for all other purposes. If there’s trip chaining, the required frequency is so high that operating costs become unaffordable; a 5-minute wait for a bus may well be unconscionable.

Outside dense cities, suburbs should have a structure of density in which all the plausible destinations are within walking distance of the train station, permitting chaining walking trips with a transit trip. With such structure, the minimum viable density is lower, because buses can connect to the train with a timed transfer and have longer stop spacing as the destinations are all at the town center. In effect, such a structure gives the town center most of the convenience benefits of a shopping mall even without other features such as enclosure and single ownership of the real estate.

Infrastructure is scale-dependent. Public transportation makes this a lot clearer than cars – different modes are used at different scales, and the shape of the network can look visibly different as well. At the scale of short trips, the correct choice of public transportation mode is none – people can and should walk. If the city has generally viable public transit, its urban layout will equally well permit trip chaining on foot. If it doesn’t, then the priority should be to establish a transit city and not to try dragging buses every block.


  1. Richard Mlynarik

    To harp on an obsession of mine, the transit fare system (barriers, pricing) can actively work against exactly this most desriable use.

    Nearly everywhere (let’s leave Tokyo aside) fare gating results in urban rail stations having few, centralized access points, reducing the easy walking accessibility of the surrounding neighbourhood retail. When I’m lugging a package, I don’t want to be required to detour 100m or 200m to *the* (or of the the two) Official Entries to a transit stop, especially when I might have been walking all the way along the length of platform that time while not being allowed to access it vertically. Nor do I wish to have minutes of my time doing this when I’m not lugging something heavy or awkward. Transit stops should be maximally porous parts of the neighbourhood, not edifices or caverns entirely aside.

    Secondly, fare tariffs have to actively encourage hop-on-hop-off. This means making time-limited (24 hour, multi-day, 7 day, 30 day, 365 day, etc) all-you-can-eat multi-modal tickets at a low multiple of one-way tickets: the exact opposite of “commuter” pricing. Owning an urban transit pass should be a “no brainer”, a default condition of residents and workers, not a major outlay whose cost/benefit requires careful consideration or individual financial pain.

    In other words: no fare gating, Tarifverbund, Verkehrsverbund.
    But you knew that.

    • Hugh B

      I know NYC has a monthly pass, which is great for chaining. Something else that might not be as obvious is 2 hour free transfers on buses, which I sometimes use for a round trip if I’m going to do something quick.

      • Alon Levy

        New York has a monthly pass, but it’s not a great deal. It costs $121 compared with $2.62 per ride, a multiplier of 46; in Berlin it costs €81 (and apparently if you sign up for an entire year it’s down to €60/month?) compared with €2.25 per ride, a multiplier of 36. You can’t do a roundtrip on a single ticket here though – if you buy tickets one at a time you’re required to specify your origin station.

        • michaelrjames

          Such costs will often reflect the amount of political/funding support these public transit systems receive. In London a Monthly Travelcard for zones 1-2 (inner London) is £134.80 (US$169.45, €150.96) thus twice the cost of Berlin (€81) or Paris (€75.20) and 40% more than NYC’s. London’s single-day card is £13.10 (€14.67) which is the same as a Paris Carnet de 10 (single-ride tickets, €14.90) and only 36% cheaper than a weekly Paris Navigo Pass (22.80€) for all zones.

          Note, that in typical British nickel-and-diming pricing structures, it is tricky to make exact comparisons. I think you can get a degree at Oxbridge in this art. While you can buy zones 1-2 for the monthly you can only buy zones 1-4 for the single-day, which is beancounter logic in explaining to the plebs that it is “worth” this high cost. A monthly travelcard for zones 1-4 is is 194.00 (US$243.87, €217.17) and you don’t want to know what the zones 1-9 costs (and yes, nine zones!).

          These prices would have been even more shocking without the reduction in the ForEx rate of the GBP over the last few years. In fact the absurd historic overvaluation of the currency has been a major driver of why the UK always seems so expensive and out-of-whack with comparable economies. It might be one of the very few and small cold comforts of Brexit (except they import most stuff which will become even more expensive).
          Another way the Brits make everything more expensive than necessary is by privatising natural monopolies and then of course not properly regulating their behaviour. The railways. The 3 London airports (into the single company! most expensive airport service charges in EU). HS1 was supposed to be built via PFI (private finance initiative =PPP) but it was a total disaster and had to be completely bailed out by the state. It cost £5.8bn when it opened in 2007 (12 years after Eurostar began operation–at lower speeds on the British side). Then the state sold a 30 year lease on it in 2010 for £2.1bn to an entity called HS1 Ltd (mostly Canadian Pension Funds) who charged the various users (mostly Eurostar and some local trains) fees to use the line. Then in 2017 HS1 Ltd sold it to another consortium for £3.6bn. Last week this new owner announced massive increases in their charges: “Eurostar claims that on a per km basis, access to HS1 is four times more costly than the Lille – Brussels high-speed line and 55% more expensive than using the Paris – Lille high-speed line.” So there is going to be a fight about it but in the UK there will be no intervention in the “free market” (even if this infrastructure was built by public funds, “privatised” for 36% of construction cost, and it’s a monopoly) so it will be Eurostar travellers who will pay. And likely British business and tourism. Combined with Brexit, I suspect there might be some more self-inflicted damage. I guess some Brits weren’t happy with wrecking their rail network and having their first and only HSR (Eurostar using HS1) be a relatively good deal!

  2. df1982

    Theoretically you can’t do a round trip, but in practice I don’t think it’s policed at all when ticket-checkers do the rounds: they’re mainly focused on the time being valid. It also doesn’t make much sense to my mind: why should a two-way 5-minute tram ride cost double a 2-hour ride from (say) Schönefeld to Spandau? There are plenty of other cities have time-limited tickets without excluding round trips.

    • Paul

      Yes, Switzerland has zone-based fares in the urban areas which creates some interesting possibilities. You can go one stop on a Eurocity train or take 3 trips on the same fare as long as it stays within the zone(s) and time limit.

  3. adirondacker12800

    I have a choice of supermarkets within walking distance, and Berlin is not an especially dense city. In Paris, which unlike Berlin is especially dense, I walked to the hypermarket…… when I lived in Providence, I walked to the supermarket, but it was located right next to a freeway exit and had ample parking.

    It’s 2019, Fresh Direct has been around for a long time. which is just supermarket that delivers, where you can place the order online instead of over the telephone. And has competitors.

    If you own a car you are going to go to the supermarket once a week to stuff your ginormous refrigerator full. In the US….. the housing projects have off street parking…. Those lovely transit villages being built next to the train station are going to have at least one parking space per unit, probably two, in most places. And be filled with people who have the kind of job that can be served by transit. In other words they’ll be able to afford cars. It would be nice if the transit village had a small grocery store where they could pick up a quart of milk, a loaf of bread or refills for their single serve coffee machines, maybe even an organic free range… TV dinner… that they can throw in the microwave. If there isn’t something next to it that’s artisanal hand crafted upper middle class fast food with quinoa. But they are going to drive to the supermarket once a week and fill their ginormous refrigerator. And get a 12-pack of stuff instead of buying it one at a time.

    I dipped briefly into this.

    In the 2010 census Bloomfield had a density of 8,920 per square mile. Bloomfield isn’t going to annex anything. They are getting denser. 8,920 is denser than most places in the US. The condos have parking and most of the gushing about pedestrians and transit is really about having it make sense to people in cars. Or to people who had their first two days in a row of pedestrian experiences when they went away to college. . . well marked crosswalks are nice. For drivers who think pedestrians are exotic. People in metro New York, in quiet neighborhoods, don’t seek out crosswalks and if the corner actually has a traffic light, blithely disregard it if there is no traffic. Crosswalks, traffic lights, signs that are car scaled not pedestrian scaled… a lot of it is about cars.
    ….ShopRite of Brookdale, Brookdale is on the other side of town from Watsessing, has on line ordering. If Fresh Direst hasn’t spread it’s tentacles that far out, yet, I’m sure ShopRite of Brookdale would be more than willing to give your grocery order to an UberEats driver and send it on… It’s 2019, upper middle class people don’t have to walk to the grocery store everyday because they don’t want to carry more than four bags.

    • Alon Levy

      Fresh Direct are… the people who will send you a basket of vegetables without any choice of what you want to eat? Or am I missing something?

      • adirondacker12800

        It was Fairway Supermarket on-line. It’s got everything you would expect in a supermarket. Someone in the distribution center in the Bronx packs it into box and their own delivery driver puts it at your door. You don’t have to schelp standardized heavy or bulky stuff. .. A can of Campbell’s soup is a can of Campbell’s soup no matter where you buy it, paper goods, cereal, pasta, laundry or dish detergent……. You don’t want to schlep they will deliver almost anything you want. If you don’t like their fresh stuff you can stop in Gristede’s twice a week and get meat and vegetables. Though some vegetables it doesn’t really matter, things like bags of potatoes or onions. It’s New York, there is delivery…

      • Bjorn

        Home grocery delivery isn’t just a NYC thing anymore. A few of the mid-market grocery chains here in the Midwest have offered home delivery for about $5 (sometimes waivable above a certain spending threshold) for a few years now. I haven’t tried it yet, but a friend who doesn’t own a car has and has no complaints.

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