I am most interested in something along the lines of: "4.3 Distance- penalized trip-weighted (calculating the Walk Score at all stops along the way) service-level summing." With that proposal (4.3), it does look as if nearby stops on the same line may be counted, even though those access points wouldn't offer additional value (as Tim Sobota pointed out). �Maybe this is jumping in the weeds sooner than necessary -- I assume this would get worked out later. �Jarret Walker (humantransit.org) points out that "transit planners are often trying to take stops out and/or implement policies that create consistent and generally wider spacing" (http:// tinyurl.com/yesz6h8). �Weighting the transit score by the number of stops in the area won't be very useful. �Additionally, the distance_penalty shouldn't be so great that it significantly reduces transit scores in the region where the system has widened stop spacing. I'm not a fan of the idea of weighting the trip values differently according to mode � rail vs. bus, for example. �The "distance- penalized trip-weighted�" approach will show if there is a difference in service speeds that makes more of the city accessible, anyway. �I acknowledge that there are differences in ride quality between different types of vehicles. �But the distinction between bus and rail in terms of service quality, station amenities, (and who each is for) etc. should, and is, blurring. �If people really want to be near light rail, the alignments and stations are usually pretty easy to find even without a transitscore. -Aaron
http://www.trilliumtransit.com/blog On Nov 5, 11:36�am, T Sobota <tsob...@cityofmadison.com> wrote:
Semantically as it relates to buses and bus stops, I would think one should clarify that accessiblity is related to (unique) scheduled trips that serve a bus stop (or stops). For an address in the "center" of a neighborhood, where the individual could just as well walk two blocks west to a bus stop bus to catch the bus - or two blocks north to a different bus stop location to catch the same bus (the route making an eastbound right turn from one arterial to the other), the fact of being "served" by two bus stops only equates to being served by one bus (route) or however many scheduled trips. �Conversely, the north-south arterial may have only the branch of one scheduled route direction - while the east-west arterial could be carrying a trunk of trips from both that route direction as well as additional trips on another route direction/bus line. I'd also note that trips per (typical) week would seem to best encompass the various daily schedule deviations that might befall a bus stop location (i.e. weekday, saturday, sunday service, extra trips late night on a friday only, etc.) On Nov 4, 3:20�pm, Kieran Huggins <kie...@kieran.ca> wrote:
isochones = accessibility only IF you assume the attractiveness of destinations falls of linearly with travel time. �This is likely not the case, thus Brandon's question about the shape of the function.as for Jerry J, the comparison of actual to scheduled running times is a big deal so I'm glad to hear you are doing that. �Rarely is that sort of thing aired publicly. �There are a lot of reasons that there will be discrepancies, some good and some bad. �But to get you started, let me ask this question -- assume that you had the scheduled running time and you measure a distribution of running times, then how would you set the scheduled running time as a function of that distribution? �the min() ? the max() ? the mean()? the median() ? the 95th percentile? etc. �this gets into a fairly complicated set of tradeoffs between cost and reliability and passenger wait times and passenger in-vehicle travel times and layover time at terminals and en- route holding policies etc.
MikeOn Nov 4, 2:02 pm, Philip Ashlock <p...@openplans.org> wrote:I'm sure some of you have seen this before, buthttp://www.triptropnyc.com/provides a very simple visualization of accessibility based on subway metrics. Simultaneous correlation with buses would make this even more accurate.-philOn Nov 4, 12:44 pm, Tommy B Goode <tommybgo...@gmail.com> wrote:For Philadelphia your calculations are very simple at the moment. (:On Wed, Nov 4, 2009 at 12:40 PM, Jerry J <jjari...@gmail.com> wrote:
fruminator gave an excellent response with the concept of accessibility and those sources. �Many researchers in this field have translated the metric "how far you can go in 45 minutes" to the
numberof job opportunities or medical facilities (destinations relevant toatransit rider) that can be reached in this time.
check out this paper by Robert Cervero: �Tracking accessibility: employment and housing opportunities in the San Francisco Bay Area
http://envplan.com/abstract.cgi?id=a311259 At Berkeley he is the professor that has done the most research in this field (transportation and land use)
Also, I haven't read this one but it seems relevant: Measuring accessibility: an exploration of issues and alternatives http://www.envplan.com/abstract.cgi?id=a291175
I'm not at school right now, so I don't have access to the PDFs, but if you are interested in taking a look, I can download them and send them to you in a couple hours. �Also, maybe a city planner person can chime in about this also.Also, I guess I should mention that I am working on something related. �Transitshed creates travel time maps based on schedule information. �From GPS traces of buses, I am also creating traveltimemaps, and trying to find areas of major discrepancy between the schedule and actual performance of the transit system and maybe the reasons for these problems. �I only have the data now for the sf bay area (thanks to NextBus) but maybe this can help out with the transit score in the future?
I also suspect that if your value analysis controls for all the things that distinguish a train from a bus then the value of a train would be identical to a bus. :) On Mon, Nov 30, 2009 at 11:40 AM, Michael Frumin <mic...@frumin.net> wrote:
There is infinite empirical research on the subject, and of course none of it agrees. One place to start is with the brits, since they love cost-benefit analysis, which depend heavily on relative values-of-time.� eg:
wrote: I am most interested in something along the lines of: "4.3 Distance- penalized trip-weighted (calculating the Walk Score at all stops along the way) service-level summing." With that proposal (4.3), it does look as if nearby stops on the same line may be counted, even though those access points wouldn't offer additional value (as Tim Sobota pointed out). �Maybe this is jumping in the weeds sooner than necessary -- I assume this would get worked out later. �Jarret Walker (humantransit.org) points out that "transit planners are often trying to take stops out and/or implement policies that create consistent and generally wider spacing" (http:// tinyurl.com/yesz6h8). �Weighting the transit score by the number of stops in the area won't be very useful. �Additionally, the distance_penalty shouldn't be so great that it significantly reduces transit scores in the region where the system has widened stop spacing. I'm not a fan of the idea of weighting the trip values differently according to mode � rail vs. bus, for example. �The "distance- penalized trip-weighted�" approach will show if there is a difference in service speeds that makes more of the city accessible, anyway. �I acknowledge that there are differences in ride quality between different types of vehicles. �But the distinction between bus and rail in terms of service quality, station amenities, (and who each is for) etc. should, and is, blurring. �If people really want to be near light rail, the alignments and stations are usually pretty easy to find even without a transitscore. -Aaron
http://www.trilliumtransit.com/blog On Nov 5, 11:36�am, T Sobota <tsob...@cityofmadison.com>
wrote: Semantically as it relates to buses and bus stops, I would think one should clarify that accessiblity is related to (unique) scheduled trips that serve a bus stop (or stops). For an address in the "center" of a neighborhood, where the individual could just as well walk two blocks west to a bus stop bus to catch the bus - or two blocks north to a different bus stop location to catch the same bus (the route making an eastbound right turn from one arterial to the other), the fact of being "served" by two bus stops only equates to being served by one bus (route) or however many scheduled trips. �Conversely, the north-south arterial may have only the branch of one scheduled route direction - while the east-west arterial could be carrying a trunk of trips from both that route direction as well as additional trips on another route direction/bus line. I'd also note that trips per (typical) week would seem to best encompass the various daily schedule deviations that might befall a bus stop location (i.e. weekday, saturday, sunday service, extra trips late night on a friday only, etc.) On Nov 4, 3:20�pm, Kieran Huggins <kie...@kieran.ca> wrote: Since you're looking for a _general_ accessibility score, I think it would be best to calculate the stoptime frequency graph against a general ridership volume graph for the city in question. For example: one bus 20 minutes apart during rush hour is *less* valuable than the same bus 30 minutes apart in the middle of the night. Does that make sense? Might also be sage to take the direction of the service into account as well, thereby calculating a total "value area" as a combination of vectors, whose length is proportional to the frequency. Thus, an intersection with buses in multiple directions would be considerably more valuable, while hubs and stations would have the highest value. You could also factor the average speed of each vehicle into that equation (subways > express buses > buses). Without having more information about the specific visitor (like where they want to go and when), I'm not sure what else can really be done. Cheers, Kieran On Wed, Nov 4, 2009 at 2:36 PM, fruminator <mich...@frumin.net> wrote: these are 'isochrones'. isochones = accessibility only IF you assume the attractiveness of destinations falls of linearly with travel time. �This is likely not the case, thus Brandon's question about the shape of the function. as for Jerry J, the comparison of actual to scheduled running times is a big deal so I'm glad to hear you are doing that. �Rarely is that sort of thing aired publicly. �There are a lot of reasons that there will be discrepancies, some good and some bad. �But to get you started, let me ask this question -- assume that you had the scheduled running time and you measure a distribution of running times, then how would you set the scheduled running time as a function of that distribution? �the min() ? the max() ? the mean()? the median() ? the 95th percentile? etc. �this gets into a fairly complicated set of tradeoffs between cost and reliability and passenger wait times and passenger in-vehicle travel times and layover time at terminals and en- route holding policies etc. Mike On Nov 4, 2:02 pm, Philip Ashlock <p...@openplans.org> wrote: I'm sure some of you have seen this before, buthttp://
www.triptropnyc.com/ provides a very simple visualization of accessibility based on subway metrics. Simultaneous correlation with buses would make this even more accurate. -phil On Nov 4, 12:44 pm, Tommy B Goode <tommybgo...@gmail.com> wrote: For Philadelphia your calculations are very simple at the moment. (: On Wed, Nov 4, 2009 at 12:40 PM, Jerry J <jjari...@gmail.com>
wrote: fruminator gave an excellent response with the concept of accessibility and those sources. �Many researchers in this field have translated the metric "how far you can go in 45 minutes" to the number of job opportunities or medical facilities (destinations relevant to a transit rider) that can be reached in this time. check out this paper by Robert Cervero: �Tracking accessibility: employment and housing opportunities in the San Francisco Bay Area
http://envplan.com/abstract.cgi?id=a311259 At Berkeley he is the professor that has done the most research in this field (transportation and land use) Also, I haven't read this one but it seems relevant: Measuring accessibility: an exploration of issues and alternatives http://www.envplan.com/abstract.cgi?id=a291175
I'm not at school right now, so I don't have access to the PDFs, but if you are interested in taking a look, I can download them and send them to you in a couple hours. �Also, maybe a city planner person can chime in about this also. Also, I guess I should mention that I am working on something related. �Transitshed creates travel time maps based on schedule information. �From GPS traces of buses, I am also creating travel time maps, and trying to find areas of major discrepancy between the schedule and actual performance of the transit system and maybe the reasons for these problems. �I only have the data now for the sf bay area (thanks to NextBus) but maybe this can help out with the transit score in the future? Jerry On Nov 3, 12:46 pm, fruminator <mich...@frumin.net> wrote: Brandon, What you're basically talking about is well-known as a general concept called 'accessibility' which is sort of a reaction to an obsession with 'mobility.' These 2 theses should give a decent review and set of references on the topic of accessibility:
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Also, this is kind of neat for visualizing isochromes:
http://www.tom-carden.co.uk/p5/tube_map_travel_times/applet/
Sorry for waiting so long to respond to this,
Jed