The Interurban Option – Prereqs

Alon‘s had a long-running series on the comparative construction costs of transit modes in different countries. It’s good reading.

At the same time, I’ve always been a fan of the “Interurban Option” – running commuter-rail levels of service to low-density areas using rolling stock that is compatible with inner-city LRT systems. I’ve previously suggested that North Carolina’s research triangle would make an ideal location for such. But in order for lower-ridership/lower-frequency LRT to work, you need lower-cost LRT.

Chicago has a long history of interurbans operating over the “L” network. The North Shore came in on the Howard line, while the Roarin’ Elgin got on the Congress “L” at Forest Park. These trains operated all the way to the center of the Loop, as contrasted with other cities where interurbans ended at suburban terminals (e.g. Philly-69th) or duplicated the streetcar system (e.g. Pacific Electric). This kinda thing should work.

Back in the 1960’s, the CTA retrofitted some former interurban trackage into an “L” extension – the Skokie Swift, or yellow line. Construction was ridiculously cheap. Catenary had been pulled down when the North Shore Line folded, but a few miles of third rail remained extant. Rather than rebuild catenary over the entire route, wire was hung only over the unelectrified portion. To switch, trains built up speed, coasted past the end of the third rail, and raised a special bespoke pantograph designed by the PM, to switch to wire. This continued until 2004.

This sort of inexpensive construction wasn’t unheard of in the 60’s and 70’s. The San Diego Trolley originally used street-level boarding (this was pre-ADA). Calgary’s C-trains didn’t have air conditioning until quite recently (and some still don’t). Portions of Portland’s MAX and Baltimore’s LRT were single-tracked, though the latter proved short-sighted.

Similar cost-containment would be needed to make Interurbans a success. For instance, the Skokie Swift carries 7,000 riders daily. At current prevailing costs, a double-track LRT line of the Skokie Swift’s length with an ultimate ridership of 7k would have to be considered a failure, not worth the effort, fodder for a Randal O’Toole piece on the superiorities of bus rapid transit. But 7,000 riders would be quite respectable for a single commuter rail line. Many of the legacy Philly lines operate in this region, while New Mexico’s Rail Runner carries only 4500.

So let’s talk about what it would take to make Interurban – LRT vehicles at commuter rail frequencies – work.


This one’s pretty simple. Wooden ties don’t last as long as concrete, and the heavy federal match on most rail projects biases everything in favor of high capital cost/low operating cost. But wooden ties are *cheap*. This is the reason historically pretty much every railroad everywhere has used them. Moreover, a rail tie which sees 15-to-20-minute peak headways and 60-to-90-minute headways elsewhere is going to be subjected to a lot less stress than a core LRT trunk running every 7 minutes. And while the “best practices” recommendation in your project plan (and associated cost benefit analysis) is going to assume replacement on 20-year intervals, deferred maintenance as practiced by all legacy US operators will see lightly used wooden ties pushed out to a 40 or 50 year lifespan.


Most US LRT goes in with catenary befitting a German mainline railway. This is, again, an outgrowth of the US transportation culture’s bias towards front-loading capital costs. Trolley wire is cheaper, but wire is more difficult to keep properly tensioned. The increased friction from slightly slack wire increases wear on both wire and pantograph. However, for a system that runs 90-minute off-peak headways, the  additional maintenance costs are trivial compared to the cost of the primo stuff.


You can start to see the common dynamic here. Wood is cheaper than steel, but doesn’t last as long. What’s better? Electric utilities public and private invariably choose wooden poles. Only with trains do we start with stainless.


Trains are enclosed spaces. LRVs are more enclosed than commuter trains or Amtrak, since they’re not vestibuled. Being on an LRV stopped in the middle of nowhere can be somewhat disconcerting. Moving all meets to stations means the train waits for a couple minutes with the doors open (or if it’s hot outside, with the doors openable by pushing a button). This is much more pleasant for the passenger.

Moreover, delays can and do happen. Skimping on passing tracks based on an operating plan will only lead the system to be obsolesced sooner. A stop every couple miles with a passing track is good for 10-minute headways. A stop every mile with one is good for a bit over 5. This sounds like overkill until the 5:53 gets delayed by a fair trade protest until the 6:07 and the 6:32 are right behind it.


Pedestrian overpasses on low-frequency rail lines can be justified where there are multiple tracks, which are also used by 79mph freight trains that take eight miles to stop. However, most every LRT out there is capable of a 3.0mphps deceleration rate or better, which lessens the need for ped grade separation.

With at-grade ped crossings, island platforms are much safer because there is no “multiple threat” issue. The platform itself serves as a pedestrian refuge, and if there is access from both sides a “zig zag” sidewalk can be used so that all peds cross in front of or behind the train. Different agencies appear to have different preferences in this regard. Island platforms are also optimal from an operations perspective, since you can “wrong rail” trains without any inconvenience to passengers. Among other things, this allows express trains to pass locals.


In practical terms, this means that a single track should be built off-center, so that it becomes part of a later double track. At a minimum the distance off the ROW centerline should be half the minimum track spacing (e.g. 6 to 7 feet), but ideally there’d be enough room for a second track under construction as well as a row of construction vehicles. This probably means grabbing a 10′ easement along the property adjacent to the future second track. In most suburban contexts, the cost of this easement will typically be a fraction of a second track, even if you factor in the the discounted cost of a second track 20-30 years in the future.


In theory, running next to rail corridors is a great idea. In practice, this only works if the adjacent land uses don’t have rail service. Otherwise you end up like Dallas or San Jose, building gigantic multi-mile concrete bathtubs to take LRVs over industrial leads that see one train every three weeks.


A lot of suburban commercial strips have relatively continuous boundaries where the backs of the stripmalls and big boxes end and single-family homes behind. Teasing a rail line through this boundary region requires a ton of strip takes and probably some people’s backyards, but once this is done you’ve got grade crossings every 1/4 to 1/2 mile and there’s enough queue storage space between the gates and adjacent traffic signals that you don’t need to spring for a fiber interconnect. The rest of your design takes care of itself.

Similar routes exist along old land survey lines. Master-planned communities of the Woodlands/Highlands Ranch/Summerlin variety tend to make up only a fraction of the urban form. The rest of it is built out piecemeal, so that the original outlines of 50-100 acre plots can be seen from the air. In the Mountain West and the Plains these are often half- and quarter-sections; in Texas and the East they’re a little more esoteric. Following these lines you can grab parking lots, yards, etc. Garden apartment complexes are particularly easy to work with since you can take out the strip of parking along the fence, raze a building, then reconstruct the parking in its place.

All of this drives up right-of-way costs, but you also get to minimize capital and O&M outlays. And the cash saved by using a “free” roadway or highway ROW is easily wiped out by the cost of median paving or overpasses at interchanges. Find an alignment that lets you use cheap construction, instead of trying to find a cheap alignment and then letting the construction cost chips fall where they may.

9 thoughts on “The Interurban Option – Prereqs”

  1. Are you sure you’ll ever need to double track without other large changes (e.g., full grade-separation)? I guess I don’t have numbers, but I’m worried that better frequency than your 5min single track one would render and at-grade crossings useless during peak times.

  2. You should add high off-peak frequency to your list of prereqs. At low levels of investment, the rolling stock is a significant fraction of your cost, and the variable costs are low. So it’s better to have trains coming every 20-30 minutes off-peak at least, or maybe every hour if it’s really out of the way, than to have a train every hour and a half outside peak hours.

    One advantage of predictable service intervals is that on single-track lines the meets happen at consistent locations, so there’s less need to double-track. For example, Providence-Woonsocket in 25 minutes every half hour all day requires one meet, which can be constructed in Lincoln.

  3. @Dennis – I think 3-5 minute headways work just fine with gates. Obviously if you have a very high traffic crossing (e.g. something like SH 6) you’re going to want to look at grade separation, but that doesn’t need to be the train, it can be the typical freight overpass where you stick the road in the air and then one or more feeder/frontage roads cross at grade.

    @Alon – As I said in the post, I think that constructing the minimum of passing sidingss based on a “sound operating plan” will just lead the singletrack segment to be obsolesced that much sooner. If I’m running 30-60 minute off peak and 12-15 peak, I want 5-8 design so the system can recover. In your Providence-Woonsocket example, at the bare minimum I’d put in a second siding at Mineral Spring.

    For a lower density area, 60-minute headways are nice and predictable.

  4. If you’re going to have your passing sidings at stations, I would add that you should build center platforms and have people cross the tracks at grade. Some agencies don’t like ped xings which drives the cost way, way up.

  5. Do any LRT operators do that? Every time I’ve seen a ped overpass for 30-minute headways, the trains are FRA-complaint.

  6. Good point, I was mostly thinking of FRA compliant operations. The only LRT case I can think of is the MBTA Green Line D branch, which is something of a special case. There are existing ped crossings but they are trying to get rid of them. The Green Line Extension (at least as of a couple years ago) is planned to be built w no ped grade crossings except emergency exits.

  7. Definitely an odd case since the entire right-of-way is grade separated *except* for ped crossings.

    In any event, we agree. It just hadn’t occurred to me to include it since even stations where the topography suggests an overcrossing (e.g. Division or Holgate on Portland’s Green Line MAX) tend to end up at-grade. I’ve updated the list.

  8. One more thing I’d throw out for people to think about… don’t gold-plate the grade crossings. Your typical legacy surface running line, say the MBTA Green Line C Branch in the median of Beacon St, has nothing other than standard traffic signal equipment protecting it. Meanwhile your typical new LRT line, say the Expo Line in LA, has quad gates and flashers all over the place, activated no left turn/no right turn and flashing “train” LED signs. Now if all that stuff keeps some fool from turning into your train, maybe it’s worth it. But all that capital cost adds up.

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