Travel-time Maps and their Uses
Chris Lightfoot and Tom Steinberg, mySociety
This work was funded and supported by the Department for Transport.
Transport maps and timetables help people work out how to get from A to B using buses, trains and other forms of public transport. But what if you don't yet know what journey you want to make? How can maps help then?
This may seem a strange question to ask, but it is one we all face in several situations:
- Where would I like to work?
- Where would I like to live?
- Where would I like to go on holiday?
These are much more complicated questions than those about individual journeys, but one thing they all have in common is transport: can I get to and from the places I'm considering quickly and easily?
The maps on this page show one way of answering that question. Using colours and contour lines they show how long it takes to travel between one particular place and every other place in the area, using public transport. They also show the areas from which no such journey is possible, because the services are not good enough.
Our first example is about rail travel. The map below shows how long it takes to get from Cambridge Station to every other station in the UK, starting at seven o'clock on a weekday morning. This could be useful if you lived in Cambridge, and were wondering where you might go for a long weekend away and didn't want to travel more than 4 hours. We assume that people will take a taxi from a convenient train station to their destination, so long as that journey is no more than an hour. (Please see our methods page for a more detailed description of our assumptions.) You can click on any of the maps on this page to see a larger version.
The white contour lines are drawn at one-hour intervals, so the innermost, almost circular contour shows destinations up to an hour from Cambridge, the concentric one two hours, and so forth. (Technically, the contours are "isochrones", meaning lines of constant time, as for "isobars" for lines of constant atmospheric pressure on a weather map.) Places, such as Leeds, which are surrounded by little circular contours are more-accessible "islands" served by fast trains with infrequent stops; they are therefore quicker to reach than those in the surrounding areas which require lengthy changes or journeys on slower services.
The colour scale, shown on the top right of the map, is in hours of total travel time. Warm colours indicate short travel time—red for four hours or less, orange and yellow for four to eight hours—and cool colours longer journeys. The longest journey times of all, to destinations in the far north and west of Scotland, are over nineteen hours (remember that this includes waiting time, which could often be overnight). Areas with no colour at all, such as the area around Hawich on the Scottish Borders or the north-west coast of Scotland, cannot be reached at all by rail and a taxi journey of up to one hour.
The map shows that the fastest journeys are those along the East Coast Main Line north to Edinburgh, and those south to London, which is served by frequent fast trains. Everywhere in England can be reached within about seven hours (so by two o'clock in this example), and everywhere in Wales within about ten hours, though many of the fastest journeys to rural areas of mid-Wales will involve a long taxi journey. The urban areas of lowland Scotland are similarly well-connected, but areas further north are much less accessible, or even inaccessible where there are no stations within an hour's drive of a given destination.
The next map is for journeys starting from Edinburgh Waverley station, but otherwise it is the same as the Cambridge map.
Here the East Coast Main Line is even more obvious than in the preceding map; it appears as a tendril of red and pink stretching south from Edinburgh down to London.
Comparing car and train travel
Again considering journeys starting from Cambridge, this map shows which parts of the country are quicker to get to by train (red and orange), and which by car (green and blue). Yellow and light orange show areas where there's no great difference. This could be useful if you had limited access to a car and were planning where to go, or wanted to see whether it was worth hiring a car for a particular trip.
This time, contours are drawn for each hour of difference in travel time. Note also that the scale is quite asymmetric: the most time you can save travelling by train is about two hours, but—for places which are difficult to reach by train—you can save six or seven hours travelling by road.
From this map, journeys to London are quicker by train (the road travel model takes no account of traffic or urban areas, so it is pessimistic about the time saving) as are journeys to Leeds, Berwick, Edinburgh, Glasgow and other points served by trains on the East Coast Main Line. In the west of England, journeys to Exeter and thereabouts are quicker by rail, but all other journeys are quicker by road (largely because most westward journeys require a change at London or a slow cross-country train to Birmingham).
(However, the model of car journey times is very simplistic, so these results should not be taken too seriously—we hope to extend the work with a more realistic model of driving times, which may substantially change the comparative results.)
Our second example is based on public transport in and around Cambridge, which chiefly means buses within town and from outlying villages into the city center. Here we ask how early must you get up and leave your home to reach a particular place of work by public transport. In this example the destination we've selected is the University of Cambridge's West Cambridge Site, which is also home to a number of commercial employers including Microsoft.
This map shows the city center of Cambridge, and the area around the destination, which is marked by a small black circle (left middle). Again, warm colours show short journey times—in this case, later departures—but the contour lines are drawn at intervals of ten minutes, rather than an hour, so that the innermost contour around the destination corresponds to a start time of about ten to nine. Again, uncoloured areas are those not served by any services; on this map these are all fields lying outside the city itself.
Cambridge is a small city with a lot of bus services, so it is not very surprising that the whole of the city center and much of the suburbs are within twenty to thirty minutes' travel of the destination, even including waiting and walking time. Moving further out, though, the picture changes: (selected villages are labelled for orientation purposes)
The larger map clearly shows the differing level of service to various outlying villages within 5–10km of Cambridge. Areas which are connected to Cambridge by fast roads, such as the A14 which runs through Fenstanton and Bar Hill, then skirts Cambridge to the north, and continues east via Stow cum Quy (just south of Swaffham Bulbeck) are much better served than villages such as Reach, which lies well off the beaten track. Waterbeach and Great Shelford, to the north and south of the center of Cambridge respectively, are also served by train services. Even on this scale there are a few habitations with no or limited bus service and from which it is not possible to reach the West Cambridge Site for 9 o'clock purely by public transport without a long walk or an overnight journey (for instance, Rampton, to the north-east of Longstanton, or Childerley, to the north-west of Hardwick).
Looking at a yet larger scale shows a similar pattern:
This map shares the same colour scheme as the previous one—warm colours indicate short journeys, and cool colours long journeys—but the contours are at intervals of thirty minutes rather than ten. Towns such as Huntingdon, Newmarket and Ely are ideal commuter territory, as are some intermediate villages; but most outlying villages aren't connected at all.
As a comparison with transport around Cambridge, we've also drawn maps for London, a much more densely-populated area with correspondingly better transport infrastructure (you will see that there are almost no inaccessible grey areas). Here the chosen destination is the Department for Transport (DfT) headquarters on Horseferry in Westminster. Starting with the most local map:
Again, warm colours indicate short journeys and cool ones longer journeys. On this map contours are shown at ten-minute intervals, so that the near-circular one around the destination indicates the area in which you can get to the DfT by leaving the house at about ten to nine in the morning.
Moving slightly further out, nearby tube stations (St James's Park, Westminster and Pimlico) and bus routes to the south and east are important. Further south there are islands of accessibility around mainline train stations such as Brixton and Clapham Junction. On a smaller-scale map, the tube and railway lines themselves show up as chains of such islands:
On this scale, particular ill-connected areas of London are clearly visible: Hackney, Richmond and Dulwich (despite a direct train service to Victoria) both require an eight o'clock start to arrive at the DfT for our nine o'clock deadline. Compare these to the region of good connectivity stretching south and south-west from the center, along the Northern Line and mainline rail line through Wimbledon, the District line to the west, and the Docklands Light Railway to the east. On this scale individual bus routes are not particularly evident, even though they are significant everywhere that rail or tube stations are too far away to walk to in the model; contrast this with the Cambridgeshire maps above.
On this final map, of the whole Greater London area and surrounds, the contour lines are at half-hour intervals:
At this scale the suburbs of London appear to be arranged along a southwest–northeast axis, a result of good rail links to Surbiton and Twickenham (at the ends of the two red tendrils which stretch away from the center to lower left). Other rail lines, such as those to Bromley and Orpington in the southeast, are also visible, as are islands of short journey time such as Watford (northwest), Hersham and Esher (southwest); these surround individual locations with fast (c. 1 hour) journey times into central London.
We are considering various possible extensions and improvements, and we're keen to talk to anyone else interested in the work so far, or any of these ideas:
- Relating journey times to house prices
- An obvious application for travel time data are to people's decisions about where to live. By comparing journey time data for particular locations to house prices in areas nearby it would be possible to tabulate the cheapest areas to live in within a certain travel time of a desired location, for instance a person's place of work.
- Improving the road travel model to better reflect comparative rail and road journey times
- At the moment our rail travel model assumes that the final stage of each journey is by taxi, under the assumption of a uniform and isotropic road network. This is clearly inadequate; we would like to extend it using journey planning software (preferably including traffic and time-of-day effects) to produce more reliable travel time and modal comparison maps.
- At the moment the maps are constructed on the assumption that users will always choose the quickest journey under the imposed constraints. Of course in reality users also respond to other incentives, of which one of the most importantly is price. If we could obtain fare data we could show journey costs rather than times, use more realistic constraints (for instance, choosing the shortest journey cheaper than a certain amount), or comparing the prices for tickets bought on the day to those bought at varying intervals before travel.
- Improving the readability of the maps
- The maps could be made much easier to understand. Improvements could be made by refinement of the colours used and by replacing the current (OS Explorer and 1:250,000) base maps with simpler ones showing sufficient information to allow the viewer to understand the placement of the map without extraneous detail such as building lines etc.
- Incorporating reliability information
- Presently we assume that all public transport services run according to their published timetable. This means that we are more optimistic about total travel times than would be regular users of those services, who will know how often services are late, cancelled or whatever. In some cases—for instance, train services—reliability data are published, but in general this is probably better handled by a statistical model. Both reliability and users' tolerance for unpunctuality could be incorporated, so that users could state the tolerance they have for late arrival at their destination (for instance, no more than once every month) and journey times computed so as to meet that target on average.
- A real-time web service
- While our approach uses only published data and services (existing public sector journey planners such as TransportDirect), the maps are quite slow to construct; for instance, the one of London above required about ten hours of computer time; further, each one is relevant only to a particular destination or origin (and points near it). If we could speed up this process, we could generate maps on demand for visitors to a website; to do this we would need to work with organisations such as Transport for London and incorporate more specific information about services in each area, rather than relying entirely on outside services. This is an attractive idea, although it would be expensive to build.
Please contact us (email addresses at the top of the page) if you have any questions or comments. If you're interested in this area, please also sign up to the (fairly low-traffic) mySociety maps mailing list.
This work was funded by the Department for Transport, who also made it possible for us to use Ordnance Survey maps and data through their licence; without this assistance we would have had to pay expensive fees to use the underlying mapping data or to produce maps with no landmarks, which would be almost incomprehensible. DfT also gave us access to their National Public Transport Access Node database, which records the locations of train and tube stations and bus stops; without this it would have been difficult to produce any maps at all.
Although the journey planning services and software we used were publicly accessibly, almost none of the other data is available unless you pay for it, or your work falls under an existing licencing agreement. So while we set out to demonstrate how easily we could make travel-time maps from public data, very little of this work could be cheaply reproduced or extended without assistance from a government department.
That's unfortunate, because it means that innovative work by outsiders in this area can only go ahead if it's explicitly sponsored by government. If all the data we've used had been available for free, somebody else might well have done what we've done years ago, with no cost to the taxpayer. We'd love it if others extend the work that we've done, but realistically there aren't very many people in a position to do this cheaply.