Tuesday, August 24, 2010

CTA Frequency Map - Wait Time Comparisons

Jarrett Walker has expressed interest in what I am doing. He may want to link to my work. I will need to choose to suggest that he link either at PrairieStateBlue or my little used personal blog Edgewater Observer. If you have thoughts about my choice please comment. Here is my latest work. It is a comparison of different possible wait times. It has a built in legend so it should be self explanatory.

CTA Frequency Map Version 9 - Ten Minute Service Circles

(Update: Oops. I am supposed to say something like: Images derived from Data Provided by The Chicago Transit Authority.)

Here are some images of version 09. In this version I have overlaid an earlier version where line widths represent the number 0f trips a week, fatter being more trips, with the ten minute or better circles from version 08.

The 79th street bus still shows that it is the major southside east west corridor. To my lay mind it still screams BRT! I'm going to have to take a trip soon and eyeball that street fr0m end to end.

The whole system map is not as large nor clear an image as I'd like. The other images show the northside and the loop area. The loop would take special treatment for a professional version, imho.
Click the images for larger version.

Monday, August 23, 2010

CTA Frequency Map V8

(Update: Oops. I am supposed to say something like: Images derived from Data Provided by The Chicago Transit Authority.)

I'm using this space as a bit of a shared workspace. So forgive the lack of relevance to the normal postings to this blog.

CTA Frequency v8 - Frequency Via Stops

Click to enlarge.

This is a work in porgress. This particular version is more a proof of concept. Here is what Mr. Walker had to say about my previous version:

Jeff. Thanks! I object, though, to using trips/day as a proxy for frequency, because lines with really intense peak service can have lots of trips/day even with little or no all-day service. . If the point of a frequency map is to show people the network they can travel on without waiting long, it needs to be based on actual midday headway. Cheers, Jarrett

So I asked for some help in coming up with "actual midday headway" thusly:

So if I am to do a midday headway map, I suppose counting the number of trips that leave between 11:30am and 12:30pm would not do because they might send out a bunch of drivers at 11:35 all together and then no more until 12:50 when another bunch might be sent out? So is actual midday headway the time between the first trip nearest noon and the one after that? Forgive my ignorance, this is not an area of expertise, but what is a good mechanism for measuring "midday headway?" What would be a good method of calculation?

To which he replied:

Jeff. You're right, it's tricky!

You have to return to the spirit of Frequent service, and the wholereason that we're mapping it. We want people to see where they can travel ALL DAY without waiting very long.

So the real question is: "What is the longest scheduled gap between consecutive buses anytime during the midday?" The point of frequent service is that it's a guarantee, not an average., That means we are mapping the worst case, not the average case.


While working with the previous version I learned that "Shapes" provided by the CTA were not properties of "Routes" but rather "Trips." In producing this map I further came to realize that "frequencies," or goal here, is also not a property of Routes nor Trips, but rather a property of "Stops".

So using the largest table provided by the CTA, the "Stop Times" table of over two milion separate records, I created a new table that not only provided the time of arrival at each stop but also the time of the previous arrival at that stop. I then calculated the greatest time difference between arrivals between seven AM and seven PM for each stop. I then drew a circle for each stop with larger circles meaning more frequency, or less maximum times between stops. The variance in circle sizes above represent a range of maximum scheduled wait time from seven or eight minutes to thirty or more minutes. Remember that's worse case scenario. I used the same color scheme from the previous map, red and orange buses, green for el/subway and blue for express bus service.

There is a ton of possible tweaking. This is a work in progress. Be patient. I'm trying to be frequent in my updates.

Sunday, January 03, 2010

Parisifiing Chicago - Peterson Ave. BRT (Bus Rapid Transit)

Chicago has a very good rail rapid transit system. But not great. Great is Paris and London for example. Here's Paris' Metro in black with Chicago's CTA overlaid in red at the same scale. These are all subway and el lines for both cities. Since I am (just) a simple northsider I centered Paris on the north and west sides. Those are the parts of the city I know best (but I am actually familiar with parts of the south side other than Comiskey and Hyde Park.

Paris is pretty compact, at least the central part absent the suburbs, isn't it. It's also very dense population wise. The streets are narrow and the there are rarely front yards and many buildings are 4 to 7 stories high.

The thing is Edgewater has similar density. Yet all we have is a single CTA line. Which is probably about right as practically everywhere in Edgewater is within three quarters of a mile of an el stop. And much if it is within a half mile. Unfortunately there are only two ways to go, north or south. Granted that's two out of three possibilities. But the next connection to any other direction is miles away, to Ravenswood at Belmont and to Skokie at Howard.

There is a serious flaw in both Chicago's future transit planning and indeed the nation's. The flaw is that extensions and new lines are planned into areas that have no rail rapid transit service rather than in the areas that have it. Why is that a flaw? Because the greatest users of transit are those where the transit exists and where the urban densities exist to support rapid transit.

Well, of course, you reply if there is no transit then how can you use it at all? And that's a valid question absent the second caveat of where urban densities exist to support it. And yes there is some validity to build it and they will come, but that does not refute the point that we in Chicago where urban densities are appropriate still need more and better rapid transit.

Let me pose a question to Edgewaterites. Have you ever taken public transit from O'Hare to Edgewater? Wasn't pretty was it? Your choices are to go all the way downtown and then all the way back to Edgewater or transfer to a Lawrence or Foster bus at Jefferson Park and then back again onto the el.

We, and much of the lakefront, need west traveling rapid transit. The operative word here is rapid. Rapid means two things: one, faster than car traffic and two, frequent arrivals.

Car traffic brings up another important issue that Edgewater faces; namely too much car traffic. We live in the middle of a major car traffic flow and bottleneck from/to the north and west and all headed to or from the loop. It used to be loop rush hour determined but during the last twenty years it has been changing into a more equalized flow in each direction. It was so extreme before that lane reversals on Sheridan and Ridge would dedicate three lanes one way and one the other depending on whether the flow was in or out.

One of the major changes by the Aldermen of Edgewater was the elimination of those lane dedications. I wasn't involved in the decision making process but I bet the divisions and arguments for and against were similar to those going on now as concerns the return of non-rush hour parking onto Ridge between Clark and Broadway. Those opposed are concerned that traffic backups within the Edgewater neighborhood will cause sufficient frustration that drivers will begin short cutting through the residential streets. It is not a paranoid fear. It could happen even with the speed humped nature of many of our residential streets.

Actually, a rapid transit line running out Peterson Street west from the Bryn Mawr Redline station would likely soak up enough car traffic to obviate making the bottleneck any worse than it is now and therefore prevent attempts of residential shortcutting. If the line were to connect with the Jefferson Park Tansit Hub it would also create a connection to the Airport from Edgewater and even Evanston. Again the key word is "rapid": rapid in speed and rapid in arrival.

The current fad in urban rapid transit is light rail. Light rail used to be called street cars or trollies. Indeed the street car system of 1947 delivered a similar density that the Paris Metro does today. In the above map for the north half of Chicago, red are streetcar lines while blue are electric trolley buses. The other colors are diesel buses.

Streetcars gave way to buses as car congestion grew to the point that they were no more rapid, and indeed often less rapid than cars. The other issue with light rail and even street cars today is expense. They cost way too much to build, especially for a system that turns out to not be rapid.

There is a way to make streetcars faster and even faster than cars. The major way is dedicated rights of way where cars are not allowed while the minor way is to give them control over stop lights. Usually the right of way is in the center of the street with dedicated "stations" for riders in the middle of the street as well. Think of the Illinois Central line on the south side where it crosses Stony Island. So with widely separated stations and dedicated rights of way and control of stop lights street cars can go faster than cars and thus approach if not actually succeed at becoming rapid.

But here's the thing. If you do those things for buses, then they can become rapid as well. And not only cost less but be more flexible as well. You can have regular bus lines that can serve neighborhoods locally and then run express as they merge into the Bus Rapid Transit right of way.

And that is exactly what I would propose for Peterson Ave. Only I would take it a step farther and have it get onto LSD for express runs downtown. That's what many northwest siders are doing anyway and it is those people we want off of Ridge. Only now not for parking but for dedicated BRT lanes (in the middle not the edges of the street.)

Between Broadway and Sheridan the BRT might have to share the road with cars but that is a short distance and easily managed especially with the buses having control of the stoplights.

Another candidate for a BRT, I would argue, is Western Ave. For a while (maybe still) Western had express buses that only stopped at the major streets. I road one of those once during rush hour and it was pathetic. I rode from about Montrose to the Blue line at Milwaukee and Armitage. I think we may have beaten the local bus but it was just barely. One beauty of a Western BRT is that it can link up so many of the northwest and western el lines. Probably the same could be done with Cicero. I have already sent the Peterson Ave BRT down Cicero to get to the Jefferson Park Transit Hub, might as well go whole hog. And as long as we are going whole hog we throw Irving Park into the mix too. Petty soon we are approaching a rapid transit density comparable to Paris.

Let me end this post by recommending this remarkable blog whose primary focus is Bus Rapid Transit. It's http://www.humantransit.org/ After I was referred to it I found myself reading post after post in a single setting. Needless to say I highly recommend it.