## An approximation of service frequency

Here is a rather crude, though I think useful, visualization of service frequency at the stop level. Basically, I used the GTFS data from SORTA and TANK to calculate the number of times a bus stops at each stop every week. Since a week is the basic cycle period of transit(service is bad on Sunday, better on monday), this should give us a an idea of basic average frequency with the huge caveat that there’s enormous variation within each week.

Click the image to get a bigger version. There’s lot’s of interesting detail in there!

You may notice that frequency can appear vary in a single line where it doesn’t seem like it probably should:

Ludlow Avenue

In most cases, this is simply an artifact of the way I grouped stops that were next to each other and had exactly the same name. At least 2-3,000 stops of the 6,000 stops in the dataset can reasonably be thought of as pairs with one serving each direction of travel.

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Posted in: Analysis | Data | Maps
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## Reading the Frequency Map for average travel times

Here’s a little known feature of the Transit Frequency Map that’s worth pointing out. You can determine your approximate total travel time, including waiting, without having to look at a schedule. Here’s how:

• Find the line or corridor you need.
• Determine it’s approximate frequency.
• Divide that in half to get the average wait time.
• Find the travel time by counting the white dots between your origin and destination. The distance between two dots represents about 10 minutes of travel.
• Add that to your average wait, and boom, you have your average total trip time.

Let’s walk through an example. Get your map out:

We’re going from Downtown to the College Hill business district on a weekday afternoon. We’ll need to use the #17. Look at the legend and compare the line thickness to find the #17’s approximate frequency.

It looks like it comes about every 15 minutes on average. Half of that is 7.5 minutes, but let’s be pessimists and round it to 8.

Now count your dots!

That’s 40 minutes plus the 8 minute average wait, meaning a total of 48 minutes for our trip. A quick schedule check confirms this is about right. You can also get a worst-case scenario by assuming you just missed a bus and using the whole frequency value without dividing it. If the longest you can wait is about 15 minutes, the longest your trip will take is about 55 minutes.

Remember, this isn’t exact since traffic speeds and frequencies vary by time of day. But generally, It’s pretty accurate. Try it out for your normal trip and see if it works for you…Then try a new one! It’s important to note that where lines are redundant, like the #4 and #11 are between Downtown, you can add their average frequencies together and get a lower average wait time because you can take whichever one comes by first.

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Posted in: Maps | Tips & Tricks
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• ### This blog is:

A shout at a passing car.
An auto-discursive manifesto.
An excited squeal at the intersection of open-computing and public transport data.