I often wondered why suburban trains sometimes were scheduled at 20-minute headways. This seemed to be at odds with real-time demand. The preponderance of work, meeting, event, and appointment times are scheduled at the hour and half-hour. However, most suburban rail riders, around 85%, take 20 minutes or less whether by car, bus, or foot, to reach the train or their final destination. The latter drives the need for minimum 20-minute headways in order to provide reasonably convenient, if not optimal scheduling with minimal off-putting wait time for most customers. Within an hour, each train offers convenient timings to successive zones or groups of stations.
Headways of 15 minutes would seem to be even better; but this limits the ability to provide express services that can reduce overall trip time for everyone, albeit innermost stations would experience a small increase in time. The number of express services in either a 15 or 20 minute cycle is limited without an express track.
You are talking about the difference between rapid transit and commuter rail. But, truthfully, if you look at terminal timetables...arrivals and departures at key locations...during peak commuting hours, you will often see side by side departures though for different end points. Close into center city you may infact have minutes of clearences while further away it will stretch out to tens of minutes or more. Heavy rail is geared to crew and equipment availability and a need to evenly distribute the service across the time period. Shorter more frequent trains might work but the cost of a whole crew plus power may outweigh the service return on investment. Heavey rail is or was often freight rail with long blocks and a concerted effort to keep trains seperated for safety sake. I like to look at public and employee timetables then try to figure equipment and crew utilization; the more I do the more I don't envy the one whose job it is to figure it all out in the first place!!!
Rapid transit is different with buses (only one driver) and subway and light rail (one motorman, one...maybe two...conductors [no fare collecting]). You then design the system...equipment, blocks, station distances, etc., to fit the five or fewer minutes of headway needed at peak times.
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Metra-BNSF line suburban trains depart Union Station on a three-to-five-minute headway from 5 pm until 5:49 (there are a couple of odd intervals in there, which is how they get off the pattern of leaving on the even minutes). As the other commenter noted, these are zone trains, so the 5:13 is making the inner zone stops, the 5:17 the middle zone stops and the 5:22 the outer zone stops. This is a triple-track, bi directionally signaled rail line with frequently-spaced universal crossovers, so it offers considerable flexibility in operating trains on such a tight headway and with varying stopping patterns.
Rapid transit headways on the CTA can be as little as three-to-four minutes, on a double-track line. Forty-odd years ago, the State Street Subway (today's Red Line) was operating trains on a 1.5-2 minute alternating headway. The heavier-loaded Englewoods were 1.5 minutes behind their Jackson Park leader, etc. Art
I believe there are European schedules based on at least the half minute!
I apparently didn't explain my concept of "minimum" well enough. I was considering the convenience of the service cycle for the majority of riders as opposed to how close trains can run.
The minimum convienience and attractiveness of service, particularly for destinations near intermediate stations, depends on a point where headways are acceptable to the users, around twenty minutes. Less frequent service discourages use for more of the potential market; and more frequent headways attract fewer remaining potential riders. With hourly service, a sizable segment of the travel market within the hour will not be attracted. With twenty-minute service, most people will ride. More frequent service will attract only an increasingly smaller proportion of additional riders.
The other part of headways is the effect on speed in comparison with competing modes. Even if the train takes only 20 minutes and a bus takes 25 minutes, quite a few commuters will have a faster trip taking a bus that comes along every 5 minutes instead of a train that comes along every 20 minutes.
More frequent and express services are means to accommodate demand that exceeds the capacity of one vehicle or train. Express services also are a means to attract additional potential riders sensitive to time, including whether it is worth the time, literally, to travel for some purpose.
I'm quite certain you'll find the schedules are based on half-minute units of time, such as 1.5, 2.0, 2.5, 3.0, 3.5 minute, and so forth frequencies and for time points. This was, and still may be done by the CTA.
HarveyK400 I apparently didn't explain my concept of "minimum" well enough. I was considering the convenience of the service cycle for the majority of riders as opposed to how close trains can run. The minimum convienience and attractiveness of service, particularly for destinations near intermediate stations, depends on a point where headways are acceptable to the users, around twenty minutes. Less frequent service discourages use for more of the potential market; and more frequent headways attract fewer remaining potential riders. With hourly service, a sizable segment of the travel market within the hour will not be attracted. With twenty-minute service, most people will ride. More frequent service will attract only an increasingly smaller proportion of additional riders. The other part of headways is the effect on speed in comparison with competing modes. Even if the train takes only 20 minutes and a bus takes 25 minutes, quite a few commuters will have a faster trip taking a bus that comes along every 5 minutes instead of a train that comes along every 20 minutes. More frequent and express services are means to accommodate demand that exceeds the capacity of one vehicle or train. Express services also are a means to attract additional potential riders sensitive to time, including whether it is worth the time, literally, to travel for some purpose. I'm quite certain you'll find the schedules are based on half-minute units of time, such as 1.5, 2.0, 2.5, 3.0, 3.5 minute, and so forth frequencies and for time points. This was, and still may be done by the CTA.
But you do have to take into account equipment and crew availability, the fact you are on a fixed pathway, and that you have to further define yourself as either a railroad or a rapid transit system. Given perfect track and perfect equipment, enough equipment and crews, every concievable safety and fool proof signal system and train control, and enough money to pay for it all, you can run as many anysize trains as close together as you want. But all is not equal nor realiable nor cheap. I am sure both the transportation departments and the marketing departments of each mode know what they have to do for speed, convience, safety, efficiency, and at the least cost.
In the early years of the RTA (mid-1970's until about 1982), the IC Electric operated on half-hour headways on the South Chicago Branch and Main Line south of 115th Street and on one-hour headways on the Blue Island Branch and Main Line north of 115th Street. This turned out to be more service than necessary based on ridership and was cut back at the time of the RTA's financial crunch and re-organization in the early 1980's.
HarveyK400 The other part of headways is the effect on speed in comparison with competing modes. Even if the train takes only 20 minutes and a bus takes 25 minutes, quite a few commuters will have a faster trip taking a bus that comes along every 5 minutes instead of a train that comes along every 20 minutes.
and a bus that stops at the end of your block vs a train whose station is a mile away,
conversely
a bus that due to traffic congestion and narrow clogged streets can't efficiently get to your apartment building which is right next to a train station, for example Hoboken or Newport PATH stations.
My office is about .75 of a mile from NJ Transit Riverline, 15 minute headways, fast travel time and discounted fare, the entire route is deemed to be 1 zone. The feeder bus has 1 hour headways with free transfer. There's another bus that paralels the river line, minute headways, detours into a couple of industrial parks, and charges 4 zones, but is a one seat ride and stops 1 block from our office. My coworker invariably takes the more expensive and slower paralel bus to work, since he doesn't want to risk missing the feeder bus. Going home will take the feeder bus and train if he gets out of work on time, and the feeder is on time, since then it comes to our corner before the paralel bus.
We had a similar deal when I was growing up in Philadelphia. SEPTA's green line, 5 streetcar routes in subway in center city ran east-west along Market St, with the Blue line subway-elevated, on the outer ends fanned out, 1 route went to the northwest, the other 4 to the southwest on surface streets. People had a choice of a 1 seat ride via the green line, or a 2 seat ride via a north-south bus connecting to the Market St Blue line. Quite often I and others on the corner would grab whatever came first, 1 seat green line or bus connecting to the Blue line, going inbound, but would usually take the green line outbound.
Headways for the Blue line and any individual green line route were usually 5 minutes or less, more frequent than most of the connecting bus routes.
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HarveyK400 I'm quite certain you'll find the schedules are based on half-minute units of time, such as 1.5, 2.0, 2.5, 3.0, 3.5 minute, and so forth frequencies and for time points. This was, and still may be done by the CTA.
Yes, CTA still makes extensive use of the 0.5 minute increments in headways for both rail and bus lines. There are demand-driven headways (ridership of x requires y seats per hour, etc.) and policy-driven headways (demand is low, but you don't want the serivce to operate any less-frequently than every 20 minutes in the peak, etc.) which gets to your question about the attractiveness of the service. Hope this helps, Art
Here in Jerusalem, with one light rail line under construction, most bus routes operate at 20 or 30 minutes headways, with a few going to as little as 6 minutes during rush houre, only those serving very heavy traffic generators like both Hebrew U. campuses, one at each end of the 28 line. Looking at map, and thinking the city is flat, one might be tempted to ask: Why would anyone use the bus for such short distances, -- exept elderly and infirm? The answer is HILLS, some quite steep. Some Pittsburgh streetcar lines were similar.
I bet some of Pittsburgh's inclines were even shorter :)
Pittsburgh had some one-car outlying shuttles, like the Dormont - Castle Shannon shuttle, which today is an integral intermediate seciton of the via Dormont Light Railroute, but was a single-car shuttle on a single-track, but for a while operated by one PCC with loops at both ends. Other shuttles used double-end Peter-Witt lightweights. If I remembember correctly, serving downtown, two short routes required only one car on weekends, Evergreen, which was the last non-PCC line serving downtown, with one double-end car, and running north on to a cut-back on the old interurban to Butler, and fabuolous Fineview. I think both had just one car on weekends, and two during rush hours. Wasn't Carnegie - Thornton a one-car old car shuttle? Then there was the Donora shuttle off the interurban to Sharleroi-Roscoe.
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