Fine-Tune Your TravelTime Analysis with Departure & Arrival Windows

29/11/21
29/11/21
Blog post
Chris Hutchinson

With the TravelTime API, you can search and analyse the world by travel time instead of distance. The TravelTime API has several advanced parameters that allow you to fine-tune the travel time request you’re making. We’ve previously discussed the public transport change delay parameter, but in this article, we’ll take a look at another parameter: Range.

Contents

    Why should I use the Range parameter when calculating travel times?

    When using TravelTime to calculate journey times, Range can be used to set an arrival or departure window instead of a fixed arrival or departure time.

    So, for example, instead of saying “I want to arrive at 9 am”, Range allows you to make a request that says “I want to arrive between 8 am and 9 am”.

    There are several benefits of being able to configure arrival or departure windows in this way, particularly when looking at public transport: 

    • It removes the potential sensitivity of an analysis to the specific arrival/departure time chosen. For example, if the user selected an arrival time of 9 am, but the fastest train arrived at 9.15 am, this route would not be picked up without using Range.
    • It offers a more general view of a location’s accessibility. For example, when looking at patient access to a hospital, we don’t know exactly when patients will be arriving. In this scenario, setting a specific arrival time in the analysis wouldn't make sense. By using a wide range window, we can analyse how accessible the hospital is throughout the day.

    How the Range parameter works

    The range parameter can be used with any of the three core endpoints of the TravelTime API:

    • Isochrones: create and visualise reachable catchment areas based on a maximum journey time
    • Matrices: calculate a matrix of travel times between thousands of origins and destinations
    • Routes: create A to B routes with turn-by-turn directions

    Isochrones

    When Range is enabled, the resulting catchment area will combine all possible journeys that arrive or depart in the chosen range window. 

    For example, if we use Range to set a departure window of 8-9 am, any locations that are reachable by a journey that departs within that window will be marked as reachable.

    Even if one journey involves leaving at 8.05 and another involves leaving at 8.55, this doesn’t matter - they are both possible and so both are included in the overall reachable catchment area.

    Matrices / Routes

    In the case of Matrices and Routes, the Range parameter can be used to find all journeys that arrive or depart in the chosen range window. The user can then choose how many routes or journey times are returned. 

    For example, let’s imagine we've chosen an arrival range window of 12-1 pm and that there are two possible journeys that arrive within this window. One journey takes 30 minutes and the other takes 45 minutes.

    If you request a maximum of only one result, then the 30-minute journey will be returned for both Routes and Matrices. However, if you request a maximum of two or more results, then both of these journeys will be returned.

    Common use cases

    1. Analysing site accessibility

    When analysing the accessibility of a particular site, in some cases it makes sense to use a specific arrival or departure time. For example, if we wanted to understand access to a potential new office development, then choosing an arrival time of 9 am might be sensible.

    In other cases, however, it makes more sense to use a wider range of arrival or departure times. It might be that we don’t know when people will be making the journey, such as when looking at access to a hospital or other public services. Or we may just want to get a ‘best case’ view of accessibility by including journeys at any point in the day.

    In the example below, we looked at the catchment area by public transport for a site in central Sydney, to arrive at 9 am.

    The purple isochrone shape shows the catchment area with no range applied. This will only include journeys that are possible within 45 minutes with a 9 am arrival time, or in other words, journeys that depart at 8.15 am or later and arrive by 9 am.

    The red isochrone shape shows the catchment area with the same parameters but a 60-minute range applied. This will now include any journeys that take 45 minutes or less and arrive at any point between 8 am and 9 am.

    Travel time catchment area
    A catchment area with no range applied (purple) vs a catchment area with a 60 minute range applied (red)

    2. Generating multiple route options

    When looking at specific routes and journey times rather than catchment areas, it may sometimes be desirable to have multiple options to compare or choose from. When creating Routes or Origin-Destination Matrices, this is exactly what the range allows.

    For example, in the image below we are looking at the potential commute options for an employee in Singapore. 

    By using Range, we can generate several different public transport routes, which allows us to compare them in terms of both the overall journey time and the convenience of the route (i.e how many changes are required).

    Public transport route options
    Different public transport route options between two locations when using a 4-hour range parameter

    How to use the Range parameter

    There are different ways to use the TravelTime tools, and Range can be used in most of them. Specifically, these are:

    1. Using the TravelTime API directly
    2. Through the ArcGIS Pro add-in
    3. Through the QGIS plugin

    TravelTime API

    The API parameter is called ‘range’ and comes under the ‘transportation’ parameter in the request. Below is an example of a Time Map request with a range of 3600 seconds (1 hour).

    TravelTime API range parameter request


    TravelTime QGIS plugin

    In the TravelTime QGIS plugin, the field is called ‘range’ and can be found under the Advanced Parameters of any of the Advanced tools in the Processing Toolbox.

    For example, in the Time Filter Advanced tool:

    TravelTime QGIS plugin_Time Filter Advanced
    Note: this value is in seconds

    TravelTime ArcGIS Pro add-in

    In the TravelTime ArcGIS Pro Add-in, the field is called ‘range’ and can be found under the Advanced Parameters of any of the Advanced tools in the Catalog Pane.

    For example, in the Time Map Advanced tool:


    TravelTime ArcGIS Pro add-in - Time Map Advanced
    Note: this value is in minutes

    Getting started

    Using Range is just one way to use the more advanced parameters available through TravelTime to configure analysis to real-world use cases.

    By setting an arrival or departure window (as opposed to a fixed arrival or departure time), you can use the Range parameter to view the public transport accessibility of a location in more general terms, rather than at one specific time of the day. 

    When looking at A to B routes and journey times, Range also allows multiple results to be returned, giving you options to compare and choose from if required. 

    The parameter can be used both when working with the TravelTime API directly or through two of the GIS plugins that we support: QGIS and ArcGIS Pro. 

    To learn more about what you can do with TravelTime, visit our documentation or get in touch.

    To test TravelTime for your project, sign up for a free API key here.

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