In a blended HSR + Caltrain system, slowly transitioning to full grade separation over a time scale of decades, several constraints exist that will impede Caltrain's ability to add capacity to meet increasing ridership demand:
- More trains per hour won't work. Because there are only two shared tracks, the capacity of the corridor (as measured in trains per hour) is limited. It's going to be a stretch for Caltrain to operate six trains per hour per direction with HSR in the mix, so adding more is clearly out of the question until the much-dreaded additional tracks are built.
- Longer trains won't work. Train length is limited at stations such as Burlingame and Menlo Park, where grade crossings are found at both ends of the station platforms. Until these locations are grade-separated and new longer platforms are built, adding more cars to make longer trains is not feasible. In any case, most Caltrain platforms limit train lengths to 600 feet (or 7 standard-length cars), at least until they are rebuilt.
- Taller trains won't work. Today's bi-level trains already take good advantage of the available height, so there is no seating capacity to be gained by growing trains any taller.
|Loading gauge comparison,|
Russia / USA / Europe
The Advantages of Extra-Wide EMUs
The diagram below shows a cross section of three double-deck trains: a traditional European EMU of the sort coveted by Caltrain; a Caltrain Baby Bullet car; and a hypothetical extra-wide EMU with comfortable five abreast seating, a few inches wider than the Russian model described above.
- More passengers per train. With five abreast seating, 15 to 20% more seating can be provided without increasing train length or train frequency. Even in those areas without seats, more floor space is available for standees.
- More usable space. Extra width makes for more spacious and comfortable vestibules, stairs, and passageways between cars. High-traffic areas near doors, bicycle racks, restrooms, and luggage racks do not impede the flow of passengers.
- Lower crew costs. The number of conductors required on a train is dependent on the number of cars in the train. Under the present labor agreement, there is a strong incentive to keep train lengths to six cars and to maximize passenger capacity per car. Five-abreast seating reduces the crew cost (and other operating costs) per available seat.
- Future-proof HSR compatibility. Because the CHSRA has already settled on a single-level train architecture for its high-speed trains, it is likely that similar capacity limitations will drive the future California trains to be extra-wide, like the Japanese Shinkansen or the Russian Velaro. Converting Caltrain to a wider standard helps achieve future platform interface compatibility with HSR, which is not just a matter of height but also of width.
- Easier conversion to high platforms. Wider trains can be fitted with both high and low doors to accommodate a platform transition period, without cutting as badly into the seat count as for a normal size train. (The Russian example is built exclusively for high platforms, but more doors could be added on the lower level.) What's more, with high platforms built further away from the tracks, those annoying freight trains get a little bit more clearance.
- Easier vehicle packaging. From an engineering standpoint, modern EMUs are like a jigsaw puzzle where every vehicle component must find its place under multiple constraints. More width gives vehicle designers more flexibility to make everything fit, making trains more comfortable and maintainable.
Caltrain should make full use of the generous clearances available on the peninsula corridor. In a blended future where HSR limits the number of peak-hour commuter trains, extra-wide EMUs with five-abreast seating are an attractive solution for giving Caltrain more rush-hour capacity.
[Update 08/2014: this Swedish academic paper analyzes the numerous advantages of extra-wide trains in far more detail, going into cost elasticities etc.]
You make a reasonable argument.ReplyDelete
I wonder, if stations are going to be rebuilt/built from scratch anyway, why not go 4m wide for 3+3 seating? What's the physical/geometrical width limit of standard gauge?
Menlo Park and Burlingame have two option. Build longer platform to have a express train stop, or get local service only.ReplyDelete
As we see >2x ridership difference between local and express, express train should have longer train consist. We need invest longer platform only at express station, which is make sense with investment and return.
Coupling and decoupling is one of key feature of EMU. BART and VTA light rail do decoupling the trainsets after morning peak and couple again before evening peak.
Or just close one of the crossings. It doesn't sound like much of a detour.Delete
There's absolutely no technical reason why Caltrain can't uncouple 3 cars of their 5-car sets outside of rush hour. The diesels can haul 2 cars either with somewhat faster acceleration; or somewhat lower fuel consumption.Delete
Why not? I'd guess institutional inertia; management with less skill at running trains than a kid with a train-set; or FRA or union rules, in no particular order.
I have no idea about Burlingame; but at Menlo Park, the "issue" is likely to be that there are certain turns one can't make around El Camino/Ravenswood/Merrill. Locals would soon learn, though. Traffic on Ravenswood is very high, particularly at commute time (including traffic to the local high school); traffic on Oak Grove is light.
The locos are optimized for very long freight trains. The MBTA studied this for the possibility of a DMU conversion of one of its lines and found the marginal fuel consumption of an additional car is very low.Delete
ACE's previous 4th round trip was 2-car train and was discontinue 2009. 2 or 3-Car train is not problem but, their management is not motivated because of 2 conductor requirement.Delete
In addition, I am curious to see response from Bike advocate as 2-car train may have only 1 bike car.
Can Labor union accept one conductor with 2-car train?
How do these EMUs compare in performance to what has been proposed in the past?
These are the state of the art. While making them wider does add a little bit of weight, they are still very lightweight and have excellent performance. We'll have plenty of time to fly to Moscow and try them out.Delete
Clem: Longer Caltrain consists can work. Google-Earth measurements show 750 feet between cross-roads at the Burlingame Station and 925 feet clearance between cross-streets at the Menlo Park Station. Flat-panel display information systems, intelligently responsive to an arriving train’s suspension system air pressure readings, can tell about-to-board passengers several minutes ahead of an arrival which car of an arriving train has the most space for boarding. Also long trains can be especially convenient for frequent riders who are likely to ride the rail-car that stops closest to their destinations. Multiple close-together-popular stops can be quickly served by one long train making one stop.ReplyDelete
Accommodating longer trains with longer platforms, additional station entrances, and more widely distributed TYM machines along railroad property but without additional track and switches appears to be a low-cost approach for increasing line and station capacity. Increasing train lengths from 200 m to 400 m that are allowed to have a 4.4 ft/sec^2 acceleration rate, a 3 ft/sec^2 safety brake rate and a 35 second dwell, performance and safety standards which are likely to prevail along a track-section near the busiest station with a carefully designed station departure control, will raise station capacity significantly. Constrained by the conditions described above doubling train lengths will increase station capacity by 75%.
Easier conversion to high platforms.ReplyDelete
That's a good one.
There was no hint of a strategy for this (easy or otherwise) in the platform sell-out article "Caltrain should do whatever HSR says regardless of how dumb it is", while the "Caltrain should buy this one French EMU and add half-height Frankenstein pieces to it" article, while interesting, doesn't seem to lead anywhere real.
So please, do tell!
First, you will need to describe what underlies your dislike of high platforms, and which camp you align with:Delete
1) those who don't believe that there is any value in having Caltrain and HSR share the same platform interface, and who think that separate stations and platforms are a fine use of taxpayer dollars.
2) those who believe HSR could or will use a low (550 mm-ish) platform height, despite overwhelming evidence that this will never happen in the real world.
I've come to the conclusion that both of those groups are deluded.
Once you come around to this point of view, as I have, the only reasonable way forward is to convert Caltrain to high platforms over the long term. The only way to achieve this without huge up-front conversion costs or a drawn-out shutdown (neither of which would do Caltrain any good) is to procure rolling stock with two sets of doors, one compatible with the old 8-inch platforms, and the other compatible with the new high platform standard--whatever it may be. Yes, these are Frankenstein trains, but I don't have a better idea.
Perhaps you do?
Even more horrific. So horrific that MARC and AMT went out an bought some.
How long does it take to build high platforms next to active lines?Delete
SEPTA riders are expecting it to be done sometime in the 23rd Century,Delete
Some LIRR or Metro North foamer probably knows how long it takes from the time the first shovel of dirt is turned until the TVMs spit out their first ticket.
They made everything high level in time for the arrival of the M1s. HIcksville to Ronkonkama was done in the late 80s. I can't find anything about how long it took. Nothing about how long it takes NJTransit to do it either. NJTransit is slowly but surely converting stations to level boarding.... I didn't go rummaging but they are gonna have to do something about New Haven - New London if SLE starts using M8s.
What's wrong with the multilevels? It seems like a good intermediate solution to me. And if all stations ever go high platform, that far end doors could be changed to be high-level only, which could improve boarding capacity, no?Delete
All the doors open at high platforms. Nothing to be changed....Delete
Is this the "anonymous" poster who says that any platform height other than 560mm is obviously brain-dead and sub-simian; or someone else? (Until, of course, the aforesaid person decides on a different "self-evidently" optimal value for the same design point, at which time anyone who agreed with the previously "self-evident" value is given the same epithets.)Delete
It _is_ more polite than than person's usual style; but one wonders.
to Adirondacker et al: Well, go-olly. Where is CalTrain going to find UIC/TSI-compatible EMUs with this bizarro North-American-Frankenheight "feature"? Or are you perhaps suggesting that Caltrain continue to operate FITH FRA-compatible dino-trains forevermore?
What alternatives do you suggest?
_I'd_ suggest rolling stock which meets Caltrain's requirement: running the current route significantly faster than the current loco-hauled FRA-compliant consists.Delete
The link you cite says that the Pultilevel Power Cars (MPCs) are an EMU modification of Bombardier's existing bi-level, hi/low-boarding design.
By the time one adds transformers, inverters, and motors, the cars are going to be 80 tons or more. How on Earth is that going to meet Caltrain's requirements?
It's not gonna, simple as that.Delete
An empty single-level E231 Series weighs 25 t if it's a trailer and 29 t if it's a motor, and is 2.95 m wide. A bilevel trailer weighs 36 t. If the motor equipment can still fit in the bogie area, this means a bilevel motor would be about 40 t. Call it 50 t for a US-length car; we're also increasing width, but longer cars are lighter per unit of length because fewer bogies. If power scales with length this is 475 kW per motor, for a power to weight ratio of 9.5 before passengers are added. That's for the same weight to length ratio of the KISS.
The more powerful E233 Series, again assuming all cars are motors, has 700 kW per US car length. Assuming it can still be just 50 t it's 14 kW/t, which is better.
so 12, 13 tonnes per axle? If WIkipedia is to be believed M8s, which are heavy come in at 16.5 per axle.Delete
For any blended CHSR/Caltrain scheme 20 kw/tonne Caltrain EMUs would be useful for minimizing the average speed difference between HSR trains and Caltrain’s EMUs. Priority in this context means avoiding CHSR express train delay by holding local trains at passing points until the higher average speed CHSR train has passed. Following a coordinated schedule both services can run maximum performance operations without mutual interference. But when, not if, CHSR trains fall behind schedule (The CHSRA intends to use a one percent schedule pad for rarely stopping LA to SF runs competing with airplanes.) a Caltrain local will be held for a period up to the run-time difference between the local and express train while traversing from one passing track segment to another. The running time difference between a 110 mph peak speed 20 kw/tonne local caltrain run and the same peak speed CHSR with one stop at Millbrae is 8 minutes between the Lawrence and Redwood City passing tracks and 11 minutes between the Redwood City and Bayshore passing tracks.Delete
For comparison BART EMUs are listed as 600 hp for 60,000 pound empty AC traction motor car which is equal to 16.4 kw/tonne. BART’s initial 1972 service along the 28 mile distance between MacArthur and Fremont with 25 second dwells would need 18.75 kw/tonne maximum power in order to maintain their 34 minute scheduled running time with a 3.3% schedule pad. (BART’s current CPUC attenuated schedules call for a 42 minute running time between the same two stations.)
The METRA Chicago to Aurora line runs 8 morning up to eleven car trains making only two intermediate stops, Route 59 and Naperville where most of their 1,760 passengers for some trains board. Their average speed is the same as the 1972 BART run example, 50 mph, along their final 28.5 mile non-stop run to Union Station at the foot of the 110 floor Sears Tower. These trains’ are pushed by one 4,400 hp engine providing 3.3 kw/tonne traction power for the 11 car consists. These ‘zone express’ schedules requiring modest power/weight ratios is a peak-demand commuter service character that dominates suburban Chicago, New York, and the 1957 Southern Pacific SF Peninsula 1957 rush-hour service patterns.
Today Caltrain’s maximum-demand-periods are spread out over 2½ hours with a high and increasing reverse commute proportion enabling multiple useful peak demand runs for every peak demand period train. In addition the current 24 mile average trip length by discretionary riders are, according to the TCRP report 95 on Traveler Response to Transportation System Changes, transit users especially responsive to transit speed and frequency improvements. SF Peninsula regional service trains capable of rapid progress across multiple stops are especially useful for meeting the SF Peninsula’s highly variable regional demand pattern combined with a need for meshing with CHSR trains along a limited passing track right-of-way are all factors suggesting an exceptionally high power/weight ratio for new Caltrain EMUs to be the optimum solution.
It is important to reflect on the vastly different energy supply consumption patterns between traction motor and gasoline engines. Larger peak capacity traction motors have lower current carrying resistance and lower current magnitudes required in order to meet a given power requirement. On the other hand chopper control becomes moderately less efficient during low power requirement periods. Complete power shut-down while coasting or cutting-out some traction motors in a train consist during low power demand periods can reduce power supply losses during low power demand conditions. On the other hand doubling gasoline engine displacement will nearly double fuel consumption rates under low power conditions for reasons beyond the scope of this discussion.
The MBTA is doing it on a few lines (just a few, sadly). The Old Colony Lines got high platforms, but I think that was before service was restored. The Fairmount Line is getting high platforms now, while service is still running, but frequency is very low, which may make this easier, I don't know.ReplyDelete
There are also the infill stations like Fairfield Metro and West Haven, though these are a) ungodly expensive, and b) on 4-track lines.
This comment should have gone in the subthread above this. Sorry.Delete
Clem, you make your case by only listing the positive aspects of running Russian-loading-gauge trains. Please tell us: what are the downsides? Will these cars fit within the _existing_ Caltrain loading gauge -- under bridges, and within horizontal clearance on the current tracks? Wlll they run under the CHSRA Technical-Memorandum's loading gauge? Will they even be deliverable by rail??ReplyDelete
Going to a non-standard loading gauge seems a very expensive way to fix steam-era crewing practices. Surely those should have been re-negotiated when Caltrain adopted a Proof-of-Payment system?
The suggested wide trains are no higher than Plate F, so bridges are OK. It's the SF tunnels that might be an issue. And it's not a huge amount wider-- only 8 inches on each side, i.e. the width of one hand. Not what I'd call your worst nightmare of an oversize load.Delete
It's not about fixing crewing practices, it's about getting more rush hour capacity... and Caltrain already has the POP system. Just with the same crew on top, zealously checking too often and writing citations not often enough. The labor agreement I linked to is the latest, currently in force.
If you believe everything you read on Wilipedia Sapsan are 10' 8.5" wide. Nominal width for North American passenger cars is 10' 6". So a whole inch and a quarter wider on each side. Or 3 centimeters in nice round numbers.Delete
10' 6" includes hand rails and grab irons, and those dorky little door status lights that we like to put on stuff. The body width is more like 10' 0".Delete
grab irons and door lights crash into the side of the tunnel just easily as car bodyDelete
So that would mean a Caltrain width of 11 ft 4.5in? The stated width, plus 8in?Delete
As I understand it, Caltrain's waiver applies to buff-strength; Caltrain EMUs will still require hand-rails, and grab-irons, and an "F" painted on the "Front" of each loco (or powered EMU).
Actually 1T is fine for long-haul 3+2 as is - http://vi.ill.in.ua/m/640x0/377674.jpg (Ukrainian-built 1T gauge train)ReplyDelete
without increasing the car width I think the "perceived capacity" of the cars can be increased by minimizing the number of facing seat pairs on each level. It's more a matter of human behavior than actual seating capacity.ReplyDelete
Except for groups of friends traveling together on weekends I get the feeling most commuters would prefer not having to share leg space with complete strangers. It's fine for 2 people staggered on opposite seats but once those 4 seats are filled with a 3rd or 4th person it feels cramped and awkward. When waiting for one of the busier trains I always dread it when I see a Bombardier consist approach. I prefer the gallery cars, even if it means standing in the aisles. Also, this may be more of a maintenance than design issue but I hate the way toilet smells always permeate those Bombardier cars. The lower levels in particular smell like mobile latrines.
I would actually like to see Caltrain continue with the basic gallery car principles except with 2 pairs of platform level doors at each end of the car and change to an articulated design with the traction motors below (in the hypothetical configuration as follows). Each fixed unit would consist of 4 cars with blunt end cabs having walk-thru vestibules at each end. The units could operate independently as a single unit 4 car train or paired together as an 8-car train.
The lower level floor would be level throughout. There would be 4 sets of stairs to the upper level as currently except instead of converging at the center of the car they would be at the vestibule ends so you can walk up one stair and down the other when looking for a seat. No need to backtrack and create a bottleneck. With the articulated bogie design the ends of the cars could be opened up to serve as standing space or fit an ADA restroom module in to be shared with the other part of the car.
And of course these gallery cars could have sleek and modern aluminum car bodies but avoid stylized "aerodynamic" fronts that restrict modular operation and would be unnecessary for the speeds Caltrain would operate at. No need to visualize them as Franken-versions of the existing stainless steel cars either. I am thinking of something stylistically along the lines of the new BART cars designed by the BMW design group but imagine a double level version of that. It might seem brutalist but is still very elegant and functional. I know people like to complain about the old gallery cars but I feel the thing they got going for them is their spaciousness and you don't feel crammed in. I think they should take the good aspects of that and build upon it with a modern design. And finally I think Caltrain should make it easier to accommodate standing passengers for "standing room only" situations or when people just prefer to stand for their trip.
I have a totally opinion of gallery vs bombardier. Toilets smell worse on gallery than bombardier according to my nose. :)Delete
Also, while some people find 2x2 seating awkward, I don't and prefer such arrangement actually. (Plus, suspension is 10x better on the new cars) I didn't realize suspension makes that much difference. Anyway, back to the topic.
I personally prefer the 2x2 seating because it gives me more room to open the laptop (especially if table is present. On gallery cars, the seat spacing is just too tight to fully open it. I don't see it getting much larger in the future.
Clem: From your March 1, 2013 comment: “Once you come around to this point of view, as I have, the only reasonable way forward is to convert Caltrain to high platforms over the long term. The only way to achieve this without huge up-front conversion costs or a drawn-out shutdown (neither of which would do Caltrain any good) is to procure rolling stock with two sets of doors, one compatible with the old 8-inch platforms, and the other compatible with the new high platform standard--whatever it may be. Yes, these are Frankenstein trains, but I don't have a better idea.ReplyDelete
Perhaps you do?”
When purchasing inherently expensive systems with few qualified suppliers, such as EMUs, a rational cost conscious buyer will avoid unnecessarily reducing the already short list of potential suppliers by adding a requirement some potential bidders may no-longer be regularly supplying. Is there a way to avoid the need to buy duel-platform-height compatible “Frankenstein trains”? Taking advantage of Caltrain’s continuous right-of-way sufficiently wide enough to accommodate any longitudinal extension of any station platform can all Caltrain station platform sets become economically reconfigured so they will simultaneously have the ability to connect with either 8 inch or high platform compatible trains?
In addition to the 12 parallel track 4th & King and 9 track Diridon Terminals all other station boarding tracks between SF and SJ must accommodate either set of one-boarding-level-capable trains along each station platform track during a two-or-more-year transition period. One approach is to initially build high level platforms only long enough to provide for one EMU car boarding at the south end of the current 8 inch high platforms. (An exception should be made at California Avenue and Hillsdale Stations where short length temporary high level platforms 500 feet north of the current platforms appear to be a lower cost temporary platform construction effort instead of temporary 8 inch platforms over road underpass construction south of these stations.) Introduction to some electrified service immediately after the first EMU deliveries, initially late evening runs, made possible by short length high level station platforms would likely expose serious design and/or production mistakes more easily corrected if addressed before a large proportion of the new cars have been produced and Caltrain’s commitment to sustaining diesel service has seriously declined. After a sufficient number EMUs have arrived to become cab cars for all Caltrain diesel hauled trains and 8 inch platforms south of the new high-level platforms have been sufficiently extended in order to accommodate present diesel hauled rolling stock diesel service could continue without the schedule padding or extra conductor previously required to sustain wheel-chair-service. At this conversion state the high level platforms could be extended northward without boarding or alighting passenger interference.
When a few more EMUs have been delivered short consist local electric train 7/20 service could begin. This limited seating capacity EMU service would become practical if it is combined with diesel expresses scheduled to run just ahead of local electric train runs at heavy boarding traffic stations but rarely stopping on the way to distant popular stations down the line. During this early conversion stage, given the average 24 mile travel distance for riders most would be offered a faster smoother trip aboard a diesel express when available. Careful scheduling may be enough to encourage a sufficient number of riders to continue riding diesel expresses rather than jamming aboard the latest but still scarce local service EMUs.
One could anticipate an eventual FSSF track-way configuration by changing to center high platform stations which could be most economically constructed if built at the same time as an 8 inch to high platform conversion effort. Any project requiring temporary platform construction and removal in order to maintain railway passenger service while simultaneously raising station platform height and position surely costs less when Caltrain is still operating from 8 inch platforms. Temporary eight inch high platforms can be supported by low berms constructed by standard road graders and paved with asphalt which can later be sold to road builders for recycling.ReplyDelete
I've seen many cases in Germany where temporary higher-level platforms are light scaffolding bases supporting wooden decks pained with no-skid textures paint OR perforated metal decking. Relocatable, reusable, self-leveling, and could probably be assembled in one day (or overnight) on a site that was clear and graded. Consider the speed that scaffolding goes up on buildings.Delete
One potential for drama with high-level boarding will be bikers. They provide significant ridership and are very vocal. With high platforms, the entrance doors will be above the wheels in a small vestibule. There won't be much room for bike storage there, plus bikes will be in the way of passengers, handicapped, and possibly bathrooms.ReplyDelete
Already, the new comfortable Bombardier cars have been dumped on the low volume runs due to lack of bike capacity. How will bike capacity be addressed in high-level entrances. I mean, entrance will be easy, but then what? Walk the bike down the narrow staircase to the bottom level?
One idea might be to allow 2 racks (4 bikes each) in each vestibule/door excluding cab cars. On a 6 car consist, that's 12 doors (-2 for cabs), so 10 * 8 = 80 bike capacity. Bikers will have one hell of a time distributing themselves along the platform, but that's best I can think of.
I don't think a ramp would be a problem, especially on an extra-wide train. You can use those cool dutch channel ramps to provide tons of bike storage on the lower level.Delete
On those 80-bike trains today, the entrance is 51 inches above the rail in a small vestibule... same difference?
Yeah, those aren't happening with a bike...Delete
Current bike restriction (dedicated bike racks) comes from FRA regulation. Is this regulation still applicable after elctrification? I did not see such restricion in BART except blackout train. BART is not under FRA regulation.ReplyDelete
Given ridership increase, bike capacity will be conflict with standing capacity anytime soon, but happens mostly in traditional commute direction.
I suggest install folding seat in the new rolling stock. Such seat can be converted into bike space when passenger volume is low.
Reverse commute volume may not be large as traditional direction. So, uilize excess capacity for bike space is makes sense.
Caltrain need to prepare roadmap for thier bike program.
The LIRR and Metro North don't have bike racks.Delete
They carry them. They are under FRA regulation.
So does NJTrasit
I'm not going to bother to go look up SEPTA, the MBTA, MARC and Metra.
Well, the LIRR solution says:ReplyDelete
Weekdays: 4 bicycles per train - 2 in the first car and 2 two in the last car, unless otherwise directed by the train crew
Ironic that LIRR wants bikes in the first car, but BART wants them anywhere BUT first car. Wonder how these guys reached such opposite conclusions.
Either way, going from 80 bikes/train to 4 bikes per train is just not going to fly in bay area.
Most likely it's because on different systems, the most crowded and least crowded parts of the train are different.Delete
My experience has been that the end cars of a BART train are the ends. Makes sense given the relative locations of station access.Delete
Some history about the BART bike policy:ReplyDelete
Originally bikes were only permitted in the rear car. That was quite bad for dwell time, and not good for cyclists either who wanted access to all cars.
So the policy was revised and was going to allow bikes in all cars -- except that some in the disabled community complained. They wanted at least one car where they knew there would not be bikes. The first car was chosen, as it was nearest to the train operator. In practice, one finds wheelchairs all over the train, so the first-car rule is rather pointless.
It's ironical that Russian KISS don't utilise the entire width for passenger trains - 3,75 m (loading gauge T - http://cert.obninsk.ru/gost/726/009.jpg ), but use reduced loading gauge 3,4 m (1T - http://cert.obninsk.ru/gost/726/012.jpg) that is providing compatibility to industrial railways and some backwater diesel lines...ReplyDelete
2+3 alignment means that 3 persons travelling alone can sit without anyone on the adjacent seat, if the train is occupied by upt to 60%. With 2+2, only 2 persons, i.e. a 50% gain for the 2+3 setup. When considering that some people travel in pairs or larger groups anyway, the advantage is even better.ReplyDelete
The same advantage could also be achieved by 1+3 alignment, however.