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Can I talk to you about TODs? This term is an American TLA, sorry, three letter acronym, that means Transit-Oriented Development. It has become very popular since the mid-1990s as the impact of car-centric developments built in the middle of nowhere caused major congestion problems for many cities across north America.

The premise was simple. Build a railway station, on a light or heavy rail line, and build housing around that station at significantly higher densities than a more traditional suburban development pattern. It was expected that, because the train would take people to their jobs, traffic congestion would not increase as much as that from traditional suburban development.

Of course, there were problems. The train systems envisioned were typically a single line that didn’t go to many of the places that people needed to go. You need networks to make things work. The standard suburban development pattern places jobs all over the place making everywhere congested, whereas public transportation systems thrive when things are concentrated in small easy to serve areas. And this land-use plan didn’t change. Also, some of these TODs never got their train line. Some just got land allocated with the assumption that somebody else would build and run the services. Yet there is one thing that is very interesting about these transit-oriented developments without the transit, in that they had the same low levels of car parking.

You see, the premise goes that if you have lots of people taking a bus or train to work everyday, then they won’t need as many cars, so the car parking provided in such developments can be reduced, allowing the land to be more efficiently allocated to more profitable things like more houses, shops, parks, and other things that are actually valuable. Developers make more money, and people have a nicer place to live.

So what if you just build a transit-oriented development but without the transit, and measure what happens? Will people own less cars, drive less, walk more, shop locally more? Well, a study by Daniel Chatman looked into this and had some very interesting conclusions.

For example, for each mile away from good public transport, car ownership increased by a tenth of a car. Living near good public transport lowered the number of cars people owned by 27% compared with those living further away. Whilst that sounds good, we haven’t determined if this is a causal relationship or not.

Interestingly, it was not distance to the train station that mattered but the quantity of off-street and on-street car parking. Households with fewer than one off-street parking availability had 0.29 fewer vehicles per adult. Doubling the number of bus stops within a mile of the home was associated with 0.08 fewer vehicles per adult. Combining these together meant that less parking availability and more public transportation options gives 44% less vehicles in those TODs, even if they didn’t have the ‘T’ bit.

This begs a simple question in my mind. Why are places like Northstowe being forced to over-supply car parking? The new settlement will have a guided busway running through the middle of it, excellent cycleways, great walking routes, and yet the biggest determination of car ownership and therefore use – car parking availability – has been demanded to be very high.

I used to think great things about Northstowe but, with such high parking minimums, it will just become another car-dominated place causing more traffic congestion in Cambridge. Why don’t people who make these decisions read the scientific papers that study these things, or ask somebody who does? Why have parking minimums for cars anyway?