Congestion isn’t just a highway problem. It happens on subway systems, too. Zhan Guo, a professor of urban planning and transportation policy at NYU, says that part of this congestion stems from how transportation authorities draw maps of their systems. In his paper, “Mind the Map” (working paper pdf here), Guo looks at the London Underground system and argues that the Tube map “has a tremendous impact on a passenger’s perceptions and his or her usage of the transit system” since “passengers often trust the Tube map more than their own travel experience on deciding the ‘best’ travel path.” Maps are more than two times as influential as actual travel times, even for experienced transit users. The lesson, Guo says, is that maps themselves can become cost-effective ways to ease planning and operation problems.
Transit maps are not scaled models of physical reality. In the London Underground map, for instance, the correlation between actual distance and transit map distance is just .22. Distance in the Underground map represents just 4 percent of the variation of the actual spatial distance between stations.
This distortion affects travelers’ perceived options of final locations, route choices, and the attractiveness of different routes. The biggest misperception is conflating transit map distance with actual travel time. Transfer stations that look “convenient” can be mobbed by crowds, leading to long wait times. Train trips that look “long” on a map can actually be reached more quickly on foot. Ultimately, travelers “(mis)trust a transit map more than their actual experience; they often take a path that looks shorter on the system map but is longer in reality compared with alternative paths.”
Here is one particular example on the Tube:
There are two alternative paths traveling from Paddington to Bond Street station, path 1 transferring at Baker Street and path 2 transferring at Notting Hill Gates (Map a). Path 2 is about 15% slower by in-vehicle time than path 1, and the Notting Hill Gate station is to the opposite direction of the destination Street (Map b). We would expect that few passengers would choose path 2. However, more than 30% of passengers chose path 2, probably because, on the schematic tube map, path 2 is about 10% shorter than path 1, and Notting Hill Gate station is shown to the south not west of Paddington (Map b).
How should planners adjust maps recognizing the influence they have on travelers’ choices?
There are lots of options. They could redraw maps to better reflect actual distance or actual travel times. They could simply post travel times or draw attention to popular, meaning crowded, transfer stations. Planners could take the focus off individual stations and onto areas. They might note “hot” zones where crowds often form. Travelers who don’t mind a bit of inefficiency in their routes might be willing to take “quieter,” if longer, trips – especially if they have a better chance at scoring a seat. Alternatively, planners might actually remove maps and drive customers to other travel planning options, such as a mobile phone, that can direct them to the most efficient route when travelers type in information about their trip. If the map is always going to influence travelers’ decisions, maybe the best strategy is to lessen travelers’ reliance on any visual version of it?
Addendum: Tim Waters observes: “Its amazing how close everything is. When you are in the tube, the distances seem so much further. I remember a few years ago getting the tube between Leicester Square and Covent Garden! The tube map although great for planning journeys really does distort distances.” Hat tip: Martin Delaney