Seems like the best way to become a regular blogger on this site is to continually bombard the authors with Guest Posts – I’m excited about joining the team!

One of the fundamental geometric advantages of public transport is that it uses less space to shift a certain number of people, than your typical car does. This is most often talked about in terms of corridor space, with such metrics as “this railway line carries the equivalent of ten lanes of traffic” being commonly discussed. This is very true of course, but misses another element of the comparison – which is storage space. While rail and bus depots look fairly large, on a per person carried basis, they are a fraction of the space that gets dedicated to car storage – more commonly known as parking.

While these matters are generally quite logical, being able to quantify the space impact of different transport options is pretty useful when we’re looking at how to integrate our land-use aspirations with the transport projects we prioritise. A useful article by Todd Littman of the Victoria Transport Policy Institute helps by doing some of this work.

Newman and Kenworthy (1999, Table 3.9) found that automobile dependent cities average about 7 meters of road length per capita, while less automobile-dependent cities average about 2.5 meters, and parking supply follows a similar pattern. This indicates that automobile-oriented transportation increases facility land requirements 3 to 5 times. Put differently, 66% to 80% of the land devoted to roads and parking facilities in modern cities results from the greater space requirements of automobile transport.

In addition, motor vehicle traffic tends to reduce development density indirectly by increasing the need for sidewalk and building setbacks to avoid traffic noise and dust, so larger boulevards, highways shoulders and front lawns can be considered, in part, a land use cost of motor vehicle transport.

The key point here is to think about land as the obvious scarce resource it is – especially in our cities. If land is being used for wider and wider roads and larger and larger parking lots, that is land which cannot be used for buildings, parks and other – arguably more productive and desirable – uses. Littman goes on to detail this on a per capita basis:

An urban arterial traffic lane can typically accommodate about 1,000 peak-period vehicles. If the average urban automobile commuter drives 10 kilometers each way on a 3-meter wide lane, each requires 60 square meters of additional road space (3m width x 10,000m length x 2 daily commutes ÷ 1,000), plus two to four parking spaces (one at home, one at work, and a share at other destinations) that average 10 square meters for curb parking or 20 square meters for off-street parking. Each additional urban motorist therefore requires 80 to 140 square meters of land for additional road and parking space to avoid increasing traffic and parking congestion.

Compare this with other urban land uses. A typical urban resident uses about 100 square meters of land for a small-lot (400 sq. m.) single-family home with four residents, and less for multi-family housing (townhouses, condominiums and apartments). A typical employee needs about 10 square meters of office space or about 30 square meters for retail. This indicates that an automobile requires more land than a typical urban resident uses for housing, jobs and commercial activities. Automobiles more than double the amount of land required per capita.

That final sentence is critical, that automobiles double the amount of space required on a per capita basis. In other words, providing for cars halves the amount of space available for more productive activities.

What becomes particularly relevant is how this varies across different land uses – which is illustrated in the graph below:

You can really see this domination of commercial areas by roads and parking when you look at recently developed employment centres in suburban USA – with Tysons Corner near Washington DC probably being the most classic example: The ironic thing about having so much land dedicated to roads and parking in commercial centres like this is that this is most probably extremely valuable land. Obviously the zoning is fairly permissive for higher-intensity developments, obviously there’s already a number of businesses located here (the 12th largest employment centre in the USA), and it has good access to both downtown Washington DC and Dulles Airport. Yet so much of this precious land has been eaten up by roads and parking – because the auto-oriented model the places was developed around is just so extremely inefficient when it comes to utilising space.

(By the way, there are some pretty grand plans to completely change Tysons Corner over the next few decades, once the Silver Line Metro System is threaded through it).

What Littman’s work, as well as observations of areas like Tysons Corner, tells us is that if we want to be successful at utilising our urban space more efficiently, then we really need to think very hard about the contribution of transport to this goal, or how transport can undermine this goal if we continue to rely on a primary method of transportation that’s so extremely space inefficient. Furthermore, from an economic perspective if we are to utilise this huge amount of available land that’s often located in logical areas for growth and development, then we need to be providing an attractive alternative to the auto-centric planning paradigm we often get so stuck in. Quite simply, you can’t turn a Manukau or a Botany or a Westgate into the next Newmarket unless a massively lower proportion of people drive – there simply isn’t the space.

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  1. The process of “healing” Tysons Corner will be really interesting actually and should provide Auckland with a few useful pointers around what on earth to do with our own urban wastelands of Manukau, Westgate, Botany, Wairau Park, Albany and I’m sure many more to come.

  2. I think another factor that needs to be taken into account is how carparks are utilised. Looking at Tyson’s Corner, Manukau or Botany you see a huge amount of empty carparks. Why are these carparks empty? Because they are sized for a building’s peak capacity.
    For example a shopping mall is open for maybe ten to twelve hours a day. I’ll be generous and say that the carpark is filled everyday between five pm and seven weekdays and nine am to five pm (unlikely to happen everyday but I’m being generous here). That leaves twenty two hours each weekday and sixteen hours each weekend where a large percentage of the carparks are empty.
    A business is likely to have a full carpark between nine am and five pm and be empty for much of the time. This gives a total of 128 hours each week where the carpark is not even doing its job of storing cars.
    This has lead me to conclude that a good first step in reducing carparking would be to have one or two carparks that are shared around the buildings of the area. This would have the effect of reducing the amount of land given over to carparks, increase each carparks utilisation rate and encourage areas to provide for better walking as it is likely that more walking will be required.
    If you contrast Manukau and Newmarket (both places with huge amounts of parking) you can see the difference this has. Most of the carparking in Newmarket is confined to several parking buildings that are shared between businesses of the area. Whereas every building in Manukau has its own carparking.

  3. Space is something that has been either neglected or extremely simplified in economic/engineering models and therefore, rarely gets mentioned. Shoup touches on this with his section on Mobility Vs Proximity where accessibility consists of the balance between these two. Proximity, or to a large degree the ‘spatial footprint’ of transport infrastructure, is the ability to interact — after all, the purpose of a transportation system is to increase people’s ability to interact.

    Balancing these two facets of accessibility is the role/difficulty of transportation systems. Fair to say, we have done so well thus far.

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