What proportion of these cars on Melbourne's Punt Rd are cruising along looking for a kerbside parking spot? (source: ABC)

The Ford Motor Company’s head of research, James Buczkowski, says the company is working on technology that will help reduce traffic congestion by tackling the problem of motorists cruising for kerbside parking (Car makers believe they’ve found a way to ease road congestion):

Thirty per cent of congestion is caused by people looking for parking spaces, so there’s a strong motivation to figure out that part of the problem.

I expect Mr Buczkowski’s plucked the 30% figure from Donald Shoup’s book, The High Cost of Free Parking. According to Professor Shoup, studies of eleven cities on four continents undertaken between 1927 and 2001 found that cruising for on-street parking generates about 30 percent of the traffic in CBDs; the average cruise time is 8 minutes. (1)

He cites a study he did of a 15 block district in Los Angeles where cruising for on-street parking created 950,000 miles of excess vehicle travel per annum, in the process consuming 47,000 gallons of petrol and producing 730 tons of carbon dioxide.

Ford is looking at whether the sensor technology already routinely built into cars could be used as “a kind of map to guide drivers to the best area for parking”.

But hang on; could that 30% figure really be right? Could nearly a third of all traffic congestion actually be due to motorists cruising for parking at the side of the road? It doesn’t sound right to me, at least not for Australian cities. It doesn’t pass the “sniff test”.

Consider that most traffic congestion is in the morning and afternoon peaks. I really doubt many drivers set out in the morning peak intending to cruise around at the end of their journey until they chance on a parking spot in the street.

I expect peak hour drivers sorted out a regular parking spot long ago, probably in a private carpark. Cruising for a kerbside parking spot seems an even more unlikely cause of afternoon peak congestion when most traffic is workers heading home.

I don’t think many drivers would cruise a congested motorway in the hope of finding a parking spot given stopping isn’t even permitted; similarly, you can’t park on a congested arterial road that’s a clearway in peak periods!

With an average commute of 13.6 km for Sydney drivers, almost all congestion is caused by vehicles “on their way” to somewhere, not tootling around looking for somewhere to reverse-park once they get there.

Another reason to think twice about the 30% meme is Professor Shoup’s figure refers, as I’ve noted before, to cruising for parking in the city centre. Most traffic congestion, however, actually occurs on major arteries outside the CBD.

In fact in Australian cities, the great majority of jobs aren’t in the CBD, they’re in the inner city and suburbs. For example, only around 15% of all metropolitan jobs in Melbourne are within a 1.5 km radius of the Town Hall.

It’s also instructive that a nation-wide study of cruising behaviour in The Netherlands by researchers from the Tinbergen Institute found that while 30% of car trips involve some cruising, the average cruise time is a mere 36 seconds.

I don’t doubt the search for scarce kerbside parking can contribute to traffic congestion in some circumstances, but I suspect those situations are pretty limited. Almost all traffic congestion is caused by motorists who know where they’re going and where they’re going to park. (2)

The problem is there’s too much demand relative to capacity. Parking is part of that problem because there’s too much of it, not too little. It looks to me like the “30%” meme has jumped the fence and gone feral.

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  1. The Shoup paper says one of those studies was apparently done by David Hensher on Sydney CBD in 2001; it apparently says the reported average search time for curb parking was 6.5 minutes. But when I examine Prof Hensher’s CV, the closest candidate paper I can find is this one by Hensher and King but  it doesn’t even mention cruising much less estimate a number. Odd.
  2. I’ve cruised for parking on occasions e.g. going to a restaurant or pub in the inner city on a Saturday night (not usually congested though) or, perhaps more often, in a shopping centre car park (not a street). I’ve also lived in places where you wouldn’t expect to get a park every time in front of your house (but usually not congested and nothing like an average 8 minute cruise).