I want to absolutely dispel the misconceptions some seem to have about Link’s capacity. In fact, I want to challenge the assumptions that go along with it being labeled “light rail” at all. While there are no hard and fast distinctions between light rail, heavy rail, and other terms such as “metro”, they each carry with them our personal experience and prejudices. 

When I think of light rail, I tend to think of two car trains, often in street right of way. There are a lot of examples of this. Portland is limited to two car trains, and runs in the street in downtown. Salt Lake City is similar, I believe, and Phoenix looks like it has only one car platforms! Denver has been two car for a long time, and is now changing that. These systems carry a lot of people – but nowhere near as many as, say, a Paris metro line.

Different parts of Link will have different needs, but all parts of Link will be able to accomodate four car trains. Each car has 74 seats, with a comfortable capacity of double that, and a maximum capacity of 200. When we start running, we won’t be filling that up – we’ll start with two car trains, and add more as they get full.

At first, Central Link will run as often as every six minutes during peak times – so with two car trains, that’s 400 per train times ten trains an hour, or 4000 people per hour per direction (pphpd). That’s more than most bus lines do in a day – in an hour. That’s the maximum capacity of many light rail systems, in total.

This is where Link is just a little different.

When University Link opens, we’ll already need three car trains during some times of day – and we’ll likely run them more often between downtown and the UW, maybe four minutes instead of six. Three car trains every four minutes takes that 4,000 pphpd and kicks it up to 600 per train, 15 trains per hour – or 9,000 pphpd. There are very few light rail systems that can do that – but quite a few metros start there in capacity.

So how about ST2? Initially, Link will run in a few overlapping segments, for service as often as every three minutes downtown. By then we’ll be at four car trains quite a bit of the day – so 800, 20 times an hour, 16,000 pphpd. That’s not light rail territory.

In ST3, with extensions to Everett, Tacoma, and Redmond, the main line will cap out at service every two minutes – but there are other changes that can be made to increase capacity even a little farther. With just the trains we have, that’s 800 people on 30 trains an hour, or 24,000 pphpd. We can also later use cars with cabs at one end instead of both*, so we don’t have a bunch of cabs in the middle of the train taking up space. That could get that 800 up to 850 or 900, and if we went a bit further and used a single vehicle the full 120m length of the platforms, it could look more like 1000 or even 1200. You can do other things, too, like taking out some seats for more standing room as they do in Japan, although I can’t imagine we ever will on this line.

These are not light rail numbers. They’re not full metro numbers – our platforms are only half as long as many New York City subway platforms – but we’re also not going to be the Big Apple anytime soon. 24,000pphpd could serve this city for a hundred years – and it’s well over light rail volumes – so I like to call Link a light metro.

By the way, just to compare – a lane of highway typically carries about 2000-2200 vehicles per hour, each with some average a bit over 1 person. 1.2 is a typical estimate during commute times. Building this system is the equivalent of getting a long term benefit of twenty more lanes of highway from Northgate to downtown (ten each way), and a bit less than that in the outskirts (just because we won’t run trains at these frequencies all the way to Redmond and Lynnwood – there isn’t demand).

The next time I hear “we should have built a subway”, I am going to link that person to this post. We’re pretty much getting one – it’s more than enough to meet our needs for a century in the corridors where we’re building it.

*These are little ASCII trains to show what I mentioned above. The dashes each represent roughly 50 people, and the angled brackets are cabs. The square brackets are cabless ends. The first one is what we can do with the trains we have. The second is how Portland is getting a bit more space, third is what we could do with trains like Dallas (DART), and fourth is what’s possible with the line we’re building, if we need more capacity in 70 or 80 years.

28 Replies to “Service Frequency and Capacity on Link”

  1. Concise, succinct, and well stated. It has been clear for some time now that even w/ street running along MLK, ST’s Link will be qualitatively different thatn many systems elsewhere in the US – the term “light metro” seems most apt.

  2. its called light rail because the definition of light rail is that it uses overhead wires and can operate in mixed traffic. metro’s can’t because they use a third rail.

    1. There isn’t a definition, really. It’s just common usage.

      SkyTrain in BC is third rail, but it’s considered light rail in documents TransLink uses.

      Japan’s high capacity intracity services, like the JR lines in town, are definitely metro-class, but use overhead wires.

      I think the big reason you see a third rail is that it keeps tunnels smaller, so for mainly underground systems it makes sense. The problem is, the word ‘light’ implies things we do not want to imply.

      1. Yeah “light rail” is misleading a bit, ST2 is a very high-capacity light-rail system. One of the other measurements is the width of the cabs, and Link has fairly narrow cab sizes.

        It’s still a lot smaller than BART or DC Metro, but it’s big enough for Seattle.

        Metro, Light Rail, heavy rail, commuter rail, all of these have definitions that vary according to the person you’re speaking with.

      2. I see what you mean, but I still think it makes sense to call it light rail. One thing that I think they should do, though, is to classify Tacoma Link as a streetcar. I think it gives people a misconception of what Central Link will be like. (Going along with that, I think that, when we connect Central Link to the Tacoma Dome, they shouldn’t link up the tracks with Tacoma Link. Instead, they should extend it in a tunnel through Downtown Tacoma with less stations than Tacoma Link.)

  3. Excellent post Ben. I’m a big fan of BART and other Metro systems but considering the multipurpose capabilities of Link (a hybrid of trolley, traditional light rail, and ‘diet’ metro service) and the potential to be at grade, subway, or elevated, Link provides the best bang for the buck for this region’s HCT needs.

    1. Thank you. I think so too – I think we’ll eventually have a serious mainline metro through town, but it’ll be 60 or 70 years. We’ll get another Link-style system to West Seattle and Ballard first (and of course, other places outside the city).

    2. BART really isn’t a metro, not in the way most people use “metro”… It’s a regional rail system. But we’re getting a great system. It’s also worth noting that our Streetcars are pretty seriously people-movers relative to buses.

  4. Not to bash on light rail, because it definitely serves its purpose, but we’re talking peak legal limit of about what 24-27k per hour last I checked. 5 unit trains are the physical max and 3 minute headway is required by the squirmy outdated FRA.


    Heavy Rail can have 5-15, possibly even more cars. Seating comfortably 70+ per car. In the case of the Sounder just look at those cars. Light Rail is in NO WAY prepared for that type of logistical movement of passengers. But for what it is being setup for, it is perfect. Heavy Rail can carry 70-80k persons per hour… just check out the north east corridor. So really, there are MASSIVE differences.

    The Heavy Rail moves more people over longer distances – that’s the purpose. Light Rail moves tons of people short distances (<2-3 miles usually).

    Light Rail is perfect for Seattle. Especially since Seattle has Sounder to offload the longer distances down to Tacoma and such. Light Rail is perfect for daily commuters bouncing in and out of the city from 3-10 miles out. Anything longer than that and one can step up to the Sounder.

    Summary: The modes are being used appropriately, but they are NOT comparable in the sense you are stating above. The capacity is MASSIVELY different.

    1. Heavy rail can have more cars, but Link’s cars are really long. Link cars are 95 feet. A lot of NYC subway cars are 60 ft long, some are even 46 feet long.

    2. I believe 2 minute headways are possible. FRA doesn’t apply because this doesn’t intersect with a freight railroad.

      Paris Metro trains with 6 cars are shorter than Link with four cars (link tops out at 4, not 5). That’s heavy rail, but Link has higher capacity.

      The capacity between Link and many metro systems is similar. The new Tokyo subway line that just opened is expected to have similar ridership to Central Link plus U Link in 2030.

      You should check my numbers and see if you can find anything wrong with them. I believe they’re sound.

  5. I’ve heard 2,000 per hour at an absolute maximum, if everyone drives intelligently and you don’t have lots of merges and lane changes. So I think your lane figure may be an underestimate.

    Furthermore, when LINK is overcapacity people have to stand on the platform and wait for the next train in 6 minutes. When you put another couple of hundred cars on the road the highway collapses into gridlock.

    1. The I-90 center roadway study used 2200, so I was just taking that at face value. I think the actual measured peaks on our freeways are indeed close to 2000, you’re right.

      And I note that the only places where Link will be overcapacity, it’ll run more often than 6 minutes. :)

    2. Right, Martin. The Highway Capacity Manual states that freeways can operate with capacities as much as 2,400 pc/h/ln but only when it is a segment without merges and weaves and that free flow speed is 70 mph or greater. A highway with high traffic volume generally reaches its maximum capacity when speeds are 45 mph. So add more cars or create a bottleneck or put a ramp with lots of cars entering and traffic will slow to a crawl.

  6. Well said Ben. To build a highway with equivalent capacity would cost much more than Link. Trying to run buses to match Link’s capacity on a single line would be an operational and cost nightmare, if it’s even possible.

    I tried to explain the same to folks on the P-I boards today but I’ve given up, for good. I’ve learned my lesson and I’m never going back there ever again.

    1. I wouldn’t give up writing on the P-I boards. You never know who might be reading the comments and be on the fence regarding the measure. You could be changing their minds. Not the anti-transit zealots but the silent readers who never comment. That’s what I do anyway. Who knows how effective it is though?

      1. P-I is a disaster. I’d write a short one or two paragraph post, and link to the Mass Transit Now site or to some entries here. It’s just not getting worked up because there are three or four posters there who dominate every transit conversation with the same talking points, pretty much the exact same posts, and the same ridiculous math that they know is wrong.

        It’s not about being right or wrong to them, it’s about misleading people into voting no. I sort of wonder if it’s organized at all, but that’s probably giving them a little too much credit.

      2. I’ve read before that skeptics try to bog down the conversation by getting into petty details. What those posters are trying to do are exactly that, try to create confusion. They somehow are able to post first and respond to the threads all-day long. I wonder too, are they getting paid to do this?

        Thanks for the advice Brian and John.

  7. Great post, Ben. We should tag this post as a “Best Of” so we can reference it in the future.

  8. light metro works. I’ve come to calling Link medium rail. If you look at the first light rail lines in the US (Portland, San Diego) what they were basically trying to do is elevate (in terms of esteem) the status of trolleys- wider stop spacing, more exclusive right of way, proof of payment- BRT for streetcars. More recently, streetcars as they once were in the US (except now with better HVAC and low floors) have come back into fashion. And light rail is taking on more characteristics of heavy rail when applied to the Seattle environment.
    Modal definitions are somewhat useless. BRT is such a wide spectrum and can mean so many conflicting services. Light rail can too. Based upon light rail service design in other communities, we would do well to use some other term as you suggest. Because I agree with you- Link is on the high end of light rail capacity and service quality.

  9. Don’t forget … it is also possible to make Light Rail cars longer by adding new center sections to existing car-sets … look at what DART is doing to their LRVs in Dallas.

    I would imagine that it would be easy to add another 2 pieces to the LINK LRVs to make them cab-articulation joint-pax body-articulation joint – cab

    1. Yeah, I’ve seen that – and in fact, the same LRVs we’re using also use an extra articulation in Hiroshima’s Green Mover service (which I’ve actually ridden).

      I actually was just talking about this in an email thread… let me update the post.

  10. True, the Kinkisharyo LRV’s have the ability to add an extra section to the vehicle should ST go with that option.

    Excellent post that brought a smile to my face. Light-Metro – This is exactly what the people are getting. The ability to be elevated, to be at-grade, and to be underground and co-exist with buses.

    Link will indeed be the most unique system in the United States. It’s flexibility will be unique along with it’s presence.

    1. ST would probably need longer maintenance bays for that. I’d rather see double or quadruple length cars if we’re going to make a change like that, but who knows.

  11. Yes, this is my favorite Ben post.

    Link LRT will have a very high capacity. ST brags about it.

    It could be termed Metro-lite or heavy-LRT, especially between Northgate and the Mount Baker Station as South McClellan Street.

    There are other ways in which ST Link LRT is unique. They chose a high voltage, 1500v, to have longer distance between substations. They have long station spacing for faster travel times. It is almost a commuter rail or BART type design with its limited access.

    Of course, this high capacity comes at high cost: complete grade separation requires lots of capital. This capital has an opportunity cost; it cannot fund other transit investments that would probably be more effective.

    An issue is whether ST2 extends Link LRT too far or places it in the wrong places. Could the ST2 funds attract more riders and provide better support for growth management if used differently? During the 2007 campaign, the slower travel times provided by the south extension were an issue. Could those South King County subarea funds attract more riders if used differently? Could the East King County funds attract more riders if used to elevate several lines on tolled highways to BRT and place LRT on the BNSFRR than to provide one Link LRT with more capacity than is needed? ST never allowed that question to be answered. Can the station in the I-5 envelope in Shoreline and South Snohomish County ever develop into pedestrian oriented places? Should ST2 spend more funds to advance transit mobility in Everett and Tacoma, urban centers with complete street and sidewalk grids? Does the whole notion of “regional” rail make fiscal sense? The notion of ST3 is fantastical.

    1. The capacity isn’t needed on the Eastside? Maybe not today, but tomorrow could be a different story.

      But let’s talk frequency and service hours. On the Eastside you can’t afford to have routes running late, and you can’t afford to have them be that frequent because of ridership.

      A high ridership route on the Eastside is the 253. Check out this schedule from Redmond to Bellevue in the evening:


      Once an hour? Eastside transit riders deserve better. I’ve missed that 8:06 before, and it’s not a fun time. Operating costs of light rail are so much cheaper that we can run light rail much later, we can operate it much more frequent, and when the trains do fill up all we have to do is attach another unit — not hire another bus driver.

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