Last post for a while as I'm ruining the thread. (I didn't mean to and hope it's of benefit for someone who is following AND I offer my reasons below) I'm posting too much and they are too long. Here is my last one for a while as I don't want to ruin the thread. Warning: Last post..and long one.
People don't seem to like me posting. The problem is that the subject area of reliability and performance is something I have experience with. My experience is that there are often different perspective on capacity. That is the stereo-type that I have of reliability and performance knowledge: Namely, that everyone has a different perspective of capacity and what is possible and many times (in my personal experience with large scale systems) there is much higher capacity capabilities depending on the local experience, but it depends on the practitioners operating knowledge and team. The real capacity is not the observed one ("Show me one two minute headway system out there for lrt)"...The real capacity can be significantly higher. Also..you don't want to reach maximum capacity. There will be issues. They will be visible. For the purposes of the Jan 2019 Rail Rapid Transit Study to UBC..Max is used to derive Operational capacity.
That may sound rude, but I don't think the 4 minute headway from the UBC Rapid transit was valid to say in that the document in the fashion it was presented (as bi-directional headway). It's impossible to prove except by reading all the technical documentation and reading between the lines of capacity and reliability or finding the trusted expert that shows how you get the capacity you get and explains to you in gory detail ( Including all of his/her experience fighting or educating others in the reliability and performance fields about capacity) And the expert is the one who can get the most capacity with the least side effects. You find that guy. That guy can tell you. From what I've read....and because I know there are always difference when it comes to capacity...I still don't believe that what I said was wrong.
I also got back from migrant_coconut that 4 minutes is realistic for lrt anyways (bunching, reliability problems etc). I don't agree with either statement.
The problem with light rails in use today is that they go nowhere close to their actual capacity availability. They can push a lot more. I've read that everywhere. As such I am not going to go around to find a system in use with this max capacity headway (not practical operating capacity headway) in use. It is theoretical capacity as described. You plan to operational capacity. Also the LRT will run at less frequent intervals as they have crush capacity handling (and less bunching) than buses. Whether this is true for the Broadway corridor..it certainly is true looking forward when there are more people boarding and people are getting older and there are destinations to go to.
I think it is telling that when American transit institutions write about capacity in their federal guidelines they write tellingly that american/canadian and asian experts on transit have different perceptions of capacity:
"Various observations of peak-hour bus flows on urban
arterials provided a framework for capacity estimates. The
maximum number of buses operating on city streets was first
tabulated in a 1961 progress report of the Transit Subcommittee of the HRB Committee on Highway Capacity (2). Further listings are presented in the 1965 HCM (3), NCHRP
Report 143 on bus use of highways (4), and a 1975 paper,
Bus Capacity Analyses (5). More recent listings are contained
in the 1985 Highway Capacity Manual (1) and in the Transportation Planning Handbook (6). Selected listings are
shown in Table A-1. These references suggest maximum bus
flows of 200 buses per hour (up to 10,000 persons per hour)
where buses can use adjacent lanes and flows of 80 to 120
buses per hour where buses are limited mainly to a single
lane (experience in Asia suggests a doubling of these bus and
passenger volumes)
The Canadian Transit Handbook (7) suggests maximum flows of 90 buses per hour in mixed traffic and 120
buses per hour in exclusive bus lanes (1). These values
translate into 3,600 and 4,800 seated passengers per hour,
respectively"
What I find most telling is that the American authorities have different capacity perceptions (and these bus headways are short) than the Canadian and that asian experience is 1/2 that and double that (Canadians have a much more conservative planning culture ... and less people). Maybe there are different rules for buses? I take this as one expert having a different opinion than the other.
From here to the end I'm just going to have the link and the exerpt from the link that shows the capacities available. Not much explanation given other than the You will notice that there are words about theoretical max capacity with 1 minute cycle signal time is 2x the cycle time for light rail. This is NOT bi-directional as reported by McElhanney Consulting in their Jan 2019 report. It is also do-able as a max capacity. You don't want to hit the max capacity. You define it..and then you operational capacity second (As I mentioned many times as as the Jan 2019 report does). There is also a quote about how highly politicized traffic signal priorities get. Just like capacity discussions, it seems signal priorities have similar differences of perceptions. It has been my experience that when you challenge the experts you can do more than they are suggesting. All the different reasons as to why we only get one capacity vs another don't hold a lot to me. Actual operating experience with translink would be nice to see, but I would doubt that this would be considered the end expert opinion. Only discussing with the current leaders and current knowledge and understanding of that knowledge would change my mind. So why try? I can't possibly believe what you are selling me. I will try to listen, but capacity is black-art and full of politics. I haven't read anything that suggests I need to keep digging about 4 minutes which should still be two. I do see a lot suggesting that they could not possibly obtain all signals as green light signals.
http://onlinepubs.trb.org/onlinepubs/tcrp/tcrp_webdoc_6-c.pdf
"The degree to which local politicians and
traffic engineers will tolerate the effects of pre-emption plays a large role in determining
the effectiveness of signal pre-emption schemes."
Right from wiki:
https://en.wikipedia.org/wiki/Light_rail
"By contrast, light rail vehicles can travel in multi-car trains carrying a theoretical ridership up to 20,000 passengers per hour in much narrower rights-of-way, not much more than two car lanes wide for a double track system.[26] They can often be run through existing city streets and parks, or placed in the medians of roads. If run in streets, trains are usually limited by city block lengths to about four 180-passenger vehicles (720 passengers). Operating on two-minute headways using traffic signal progression, a well-designed two-track system can handle up to 30 trains per hour per track, achieving peak rates of over 20,000 passengers per hour in each direction. More advanced systems with separate rights-of-way using moving block signalling can exceed 25,000 passengers per hour per track.[27]
Transit Capacity and Quality of Service Manual, 2nd edition
http://www.trb.org/Main/Public/Blurbs/153590.aspx
Determining On - Street Capacity
Single streetcars in classic mixed operation can be treated as similar to buses and
capacity determined from the procedures of Part 4 of this manual, with suitable
modifications reflecting longer vehicle lengths and differences in dwell time
variability.
Where, as is often the case, light rail train lengths approach the downtown block
lengths, then the throughput is simply one train per traffic signal cycle, provided the
track area is restricted from other traffic. When other traffic, such as queuing left
turning vehicles, prevents a train from occupying a full block, throughput drops as
not every train can proceed upon receiving a green signal. A common rule of thumb
is that the minimum sustainable headway is double the longest traffic signal cycle on
the at-grade portions of the line. Equation 5-15 can be used to determine the
minimum headway between trains operating on-street in exclusive lanes or mixed
traffic.(R13,R15)
page 82/134
h(os) = minimum on-street section train headway (s);
g = effective green time (s), reflecting the reductive effecs of on-street parking and pedestrian movements (mixed traffic op
eration only), as well as any impacts of traffic signal
pre-emption;
C = cycle length (s) at the stop with the highest dwell time;
C(max) = longest cycle length (s) in the line’s on-street section;
https://ieeexplore.ieee.org/document/1622580/references#references
For many years, GRS has supplied control systems for conventional rail transit. Headways for these systems range from minutes or hours to as low as 75 seconds, In the last few years, the company has supplied control systems for people-mover applications in which minimum headways of 10 to 20 seconds have been achieved. The 75-second design headway of a model Conventional Rail Transit (CRT) system is compared with the 18-second design headway of a model Automated Guideway Transit (AGT) system from the viewpoint of potential for reduced CRT headway. It is shown that the major CRT factors responsible for this headway difference are on-line stations, train length and Safe Braking Distance. These factors are evaluated and discussed. It is concluded that a large increase in CRT track capacity should not be expected from the transfer of control technology from AGT.
http://onlinepubs.trb.org/onlinepubs/tcrp/tcrp_webdoc_6-c.pdf
"Historically, streetcar operation has achieved throughput in excess of 125 cars per
hour on a single track in many North American locations. Even now the Toronto Transit
Commission schedules single and articulated streetcars at a peak 15-minute rate of over
60 cars an hour on Queen Street East in Toronto, where several car lines share a fourblock stretch. The price of this capacity is low speed, congestion, irregular running, and
potential passenger confusion at multiple-car stops.
Despite this record, on-street operation is often raised as a major capacity constraint
for modern light rail systems, yet this is rarely the case on contemporary lines. This is
particularly true on most newer lines where light rail trains have exclusive use of road
lanes or a reserved center median where they are not delayed by other traffic making
turns, queuing at signals, or otherwise blocking the path of the trains. Exclusive lanes for
light rail are also being instituted on some of the older streetcar systems."
Signal-progression (green wave)
"Signal progression has supplanted pre-emption in many cases where light rail trains
operate in congested downtown areas. This technique gives trains leaving stations a
“green window” during which they can depart and travel to the next station on successive
green lights. The benefits of progression increase with greater station spacing as less
accumulated time is spent waiting for the progression to start at each station. The
progression is frequently made part of the normal traffic signal phasing and so is fully
integrated with signaling for automobiles on cross-streets. "
"It is useful if the train operator waiting at the first signal in a series of signals can
determine when the “green window” will start, as this allows the operator to serve more
passengers by maximizing the dwell time at the station. "
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