Page Two articles are from our reader community.

In part 1, we discussed how the limitations of our light rail system may impact its performance as a regional service. Now, we will highlight some potential issues within cities that we may face when our light rail capacity is adapted to serve high-demand suburban services.

Light rail’s need to provide high capacity and reliable mobility for the region is supported by its infrastructure. When the infrastructure means “surface running”, such as on MLK, high capacity (i.e. longer trains) is accommodated by large stations and reliability is provided by long stretches of track with uninterrupted travel. Although this means that mobility to and from the neighborhood is improved (regional mobility), accessibility within the neighborhood may be compromised.

Mobility vs accessibility

Transport engineers like to focus on mobility, which characterizes the movement of people or goods. It is a means to an end, in which mobility is required for a person to perform an activity that takes place somewhere else.

On the other hand, land use planners like to focus on accessibility. This has several definitions, but in the context of urban design, it defines the ease at which activities can be performed.

Let’s take a look at Jarrett Walker’s definition:

“Access is how many useful or valuable things you can do.”

And let’s take a look at Litman’s:

“Accessibility (or just access) refers to the ability to reach desired goods, services, activities and destinations (collectively called opportunities).”

Now there’s an important difference between mobility and accessibility. While accessibility focuses on the ability to perform activities, mobility focuses on the means to get there. If an activity is closer, it requires less mobility, and thus the accessibility may be higher. Jarrett Walker also notes this:

“If a new grocery store opens near your house, that doesn’t improve your mobility but it does improve your access.  You can now get your groceries closer to home, so you don’t need as much mobility as you did before…A lot of the work of access is simply about eliminating the need to move your body around the city in order to complete the economic and personal transactions that make up a happy life.”

The ability to perform activities within a neighborhood (accessibility), is fundamental to urban design. How can residents in a neighborhood perform their daily tasks as easily as possible, without the need to travel long distances and without the need for motorized transport?

This is achieved using various ways, among them, higher density developments, narrower streets and more pedestrian access. The solutions are up to the planners, but they often hint towards some kind of compactness in the neighborhood structure that shortens trips and allows activities to be brought closer together. The infrastructure within the neighborhood has to support that.

Limitations to accessibility presented by high-capacity light rail operations

While Link will bring mobility to surface segments (i.e. Rainier Valley) as well as some Transit-Oriented Development, its design places a limit on accessibility when it runs on the surface. It can take people farther away from the neighborhood, and it can generate development around the station, but it doesn’t allow trips to be as compact as possible within the neighborhood. This is notable in surface running applications such as on MLK.

One of the touted capabilities of our light rail system is its capacity, not because of its frequency, but because of its ability to run 4-car trains. This is necessary to support demand elsewhere in the network, but not necessarily in the Rainier Valley.

In grade-separated operations, the ability to run 4-car trains is a plus. However, on surface streets such as MLK or the planned Bel-Red corridor, this may become an issue for accessibility.

A 4-car train totals just over 380 feet (116 m) and the surface stations (such as those on MLK) built to support them meet or exceed 600 feet when ramps and access points are taken into account. Our light rail stations surpass the length of a typical downtown Seattle block length and conflict with components of accessibility. These stations are fenced off on both sides, and prevents access from any point other than the ends of the blocks they sit on. The infrastructure needed to accommodate the train’s sheer size represents a large barrier in the middle of MLK and enforces the distance residents must travel to get to “the other side”. The train itself may be accessible, but a trip starting from mid-block and ending on the opposing mid-block is separated by more than 600 feet, even though it is physically not more than 100. It removes connections across MLK, connections that will become even more important when TOD is built around the stations.

And then there is the long distances between intersections. Between S Orcas St and S Graham St, there is only one pedestrian crossing over a span of nearly 2000 feet.

These compromises are the direct result of Link’s attempt to serve both the region (through a 60-mile corridor) and urban neighborhoods (street running). It needs the reliability provided by uninterrupted movement through the corridor, but on street-level, that requires minimal intersections and pedestrian crossings. It needs the long platforms that can handle 4-car trains to meet demands elsewhere in the network, but occupies large footprints in what is to become the center of TOD. Where Link strives to provide mobility for the region, it does so at the expense of neighborhood accessibility.

If surface rail is aimed at complementing mobility, it should be scaled to support it. But in this case, Link is scaled for the need to provide mobility out of the neighborhood, rather than complementing the neighborhood in which it operates.

So what exactly are we building?

This is a question we need to answer, even if it may already be too late. Are we building a light rail system that satisfies the mobility needs of Seattle and its immediate suburbs? If so, our sizable trains that try to meet regional needs may negate the accessibility benefits when it runs on the surface. It also doesn’t serve enough of Seattle to satisfy urban mobility needs and instead, ventures out into the suburbs with a stop every 2 miles.

Does that mean we are building a regional network to connect cities in the Puget Sound region quickly and reliably? That too is questionable, because in that case, we are pushing the very concept of light rail beyond its intended use, where it may not keep up with the performance demands of regional services.

Urban mobility and regional connections are two completely different concepts that each require their unique solutions. Urban mobility is provided by an urban or suburban network with high capacity, frequency and accessibility to facilitate short trips within an urban area. Regional mobility is provided by high-performance trains that can travel between multiple cities quickly and reliably. These two concepts conflict in many different ways.

Unfortunately, it appears that we are trying to serve urban, suburban and regional needs with one mode, and in the end we may get something that serves none of them particularly well.

11 Replies to “Limitations of light rail as regional transport (Part 2)”

  1. Do you have any idea how long a two-car train takes to get through the average intersection on MLK today?

      1. I’m sure, but I’m wondering how significant the time increase will be with four cars and what constraints SDOT has to deal with today. And the last two cars will be in and out of the intersection much faster than the first two cars. I suppose I could stop being lazy and figure it out myself.

    1. ignoring acceleration, the time for a 4 car train to get through the intersection will be approx double the time for a 2 car train. does that help?

      1. remember, with only 3 at-grade stops in the valley, mean most intersections should be crossed at a near constant velocity.

      2. The problem with Link on MLK is when pedestrian and auto traffic is held up waiting for trains to pass in both directions. I often cross MLK at Orcas, both as a driver and as a pedestrian. If it’s just one train that is passing, the delays aren’t bad, but when traffic is held for a southbound train and then for a northbound train, the delay can be quite lengthy and you will see pedestrians start to jaywalk across MLK and the auto traffic will line-up in both directions on Orcas. Othello is actually the worst intersection in the valley (I think due to the high number of cars turning left from all directions). I would imagine that traffic statistics would show that it also has the highest number of traffic accidents, too.

  2. The rapid streetcar concept that was throw around a few years back probably would be closer to “scaled to support it link” (street view of Munich) and better suited to mobility within the city of Seattle.

  3. Is this a call for an inland Sounder North and more Sounder South service?

    Or my imagination at work?

    1. Yes, if you follow this logic through, Sounder service provides the high-speed, regional backbone transit service. Stops are spaced several miles apart, up to 79 mph speed. Current issues: tracks are shared with freight and owned by a freight company, precluding cost-effective off-peak service. Also, diesel power, meaning slower acceleration than electric service.

      In the 50-100 year timeframe, we should build dedicated passenger (electrified) mainline rail tracks in the Olympia-Everett corridor. These tracks would be used by both high-speed rail (Cascades) and regional rail (Sounder). Once this system is constructed (a collaboration between ST4, WSDOT Rail Division and a new federal HSR program?), Link can be relegated to a local mobility service by adding more infill stations.

      Imagine hourly service to Vancouver-Seattle-Portland and 20 minute frequency service from Lakewood to Everett, each running 90 mph or 120 mph max speed. Ideally, the new corridor would branch off the current mainline to serve Sea-Tac airport, for direct international airport service from throughout the northwest. I envision a route following I-5 up from Tacoma, using the right of way for the future South Access Road to Sea-Tac airport, a tunneled station directly underneath the light rail station, with tunneled/elevated routing back to the BNSF right-of-way between Tukwila and Boeing Access Road.

      Between Seattle and Everett, new right of way will be needed to avoid the landslides and limits on adding new tracks found along the coastal route. The I-5 express lanes would make a great ROW through north Seattle once Lynnwood link is open, and the tracks could stay in the I-5 right of way up to Everett.

      It could be done for $6-$10 billion.

  4. If we build another tunnel in downtown Seattle, I think we should consider connecting the Airport/Rainier Valley line with the Ballard Line through one tunnel and scale it appropriately. Then the North Link would connect with East Link through the second tunnel.

    Fifty years from now ST would have 3 basic lines:

    1) Airport > Rainier Valley > Downtown > Ballard > University District (scaled to neighborhood running)

    2) Everett/Lynnwood > Northgate > U District > Downtown > Eastside via I-90 (scaled for long distance running)

    3) Tacoma/South King County > Airport > (West Seattle?) > Downtown

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