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Friday, February 21, 2014

Multi-city Latin America parking study now in English

Last year, I highlighted a Spanish-language report on parking in Latin America and its launch event in Bogotá.

Now the English-language version is out. Hooray!

The full title is: Practical Guidebook: Parking and Travel Demand Management Policies in Latin America.

You can download via ITDP's website and here is a direct link to the pdf (4MB).

The study was commissioned and coordinated by the Inter-American Development Bank (IDB) and prepared by teams at Despacio of Colombia (Carlosfelipe Pardo, Carlos A. Moreno and Patricia Calderón Peña) and the Institute for Transportation and Development Policy - ITDP (Michael Kodransky, Bernardo Baranda, Xavier Treviño and Andrés Sañudo).

As the title suggests, it is an excellent resource on TDM in the region, as well as on parking policy. It also has numerous clear and compelling infographics (by Claudio Olivares Medina).

The heart of the report is the set of case studies on 12 cities from 5 countries across the region and careful comparisons between them.

The case studies were prepared by the following people and organizations:
Argentina: Clara Rasore, Andrés Fingeret (ITDP Argentina), Gabriel Weitz, Mariel Figueroa (STS Rosario)
Brazil: Danielle Hoppe y Clarisse Linke (ITDP Brazil)
Chile: Claudio Olivares Medina (Despacio)
Colombia: Carlos A. Moreno, Jorge Iván Ballesteros, Dorancy González, Carlosfelipe Pardo y Dilia Lozano (Despacio)
México: Andrés Sañudo y Xavier Treviño (ITDP Mexico).

Thursday, December 5, 2013

Want more parking? Careful what you wish for!

The #BlackFridayParking exercise was a striking crowd-sourced effort organized last week by the Strong Towns movement.

It highlighted the absurdly excessive parking supply around suburban retail in the United States. It thereby pokes fun at ludicrous minimum parking requirements.

One of the #BlackFridayParking photos via Strong Towns blog

Latin American cities please take note. South Asian and Southeast Asian cities please take note. Australia and New Zealand please take note. In fact, everywhere with parking minimums please take note! When it comes to parking, be careful what you wish for.

Strong Towns called for photos of retail parking lots on Black Friday to be shared via Twitter under the hashtag #BlackFridayParking.

The parking relevance of Black Friday, the day after the USA holiday of Thanksgiving, arises because this is traditionally the biggest shopping day of the year in that country.

Parking requirements (at the centre of the conventional suburban approach to parking policy) aim to match the peak parking demand of the year (or nearly that level). And when is that peak parking demand? Black Friday!

So surely retail parking lots should fill up on Black Friday right? Wrong. 

Please read the Strong Towns blog post that debriefs after the event. It makes numerous excellent points.

And scroll down to the slideshow of photographs from the day. Image after image (70 of them) show huge expanses of empty parking around numerous retail outlets across the USA.

Charles Marohn brings home the key message:
If you want to build a strong town, get rid of your parking minimums. Any chaos that ensues will be healthier for your city than the acres of unproductive, wasted space we have justified with a veneer of professional expertise.
Chaotic on-street parking problems can be managed. Priced public parking can be built if the demand and willingness to pay justify it.

But vast oceans of parking cannot easily be reversed. Multiple underground or podium levels of parking cannot easily be put to better use.

You may think that parking requirements are not really why retailers like Walmart are almost always set in a vast parking lot. 

And you might be right. Here is Charles Marohn on this issue:
Do you think Wal-Mart opposes parking minimums? They may on an individual site here or there, but in general, parking minimums are one of their best advantages. They simultaneously raise the cost of entry for competitors while further tilting the marketplace in favor of businesses catering to people who drive (a segment Wal-Mart dominates). It is a self-reinforcing, downward cycle. If you are pro-biking, pro-walking or pro- transit, you are anti- parking minimums.

Was #BlackFridayParking a scientific exercise? No, of course not. 

It was striking and suggestive but you might say it proves nothing. Presumably the most enthusiastic participants were parking reform supporters who went out looking for empty lots and may have been reluctant to share images of full ones.

Nevertheless, I am assuming for now that what we see here is not too extremely misleading and that plenty of suburban retail locations have very far from full parking, even on Black Friday.

But, you say, there may be other reasons for that empty parking! Perhaps many of the photographed retail outlets may be struggling and in decline. That would help explain it.

But, if that is true, then it would actually highlight another theme of the Strong Towns movement - the economic vulnerability of the car-dependent buildings-set-in-oceans-of-parking development model relative to more traditional patterns of development.

Traditional retail development in town cores can also decline of course. And many town centres across the US are indeed in a sorry state.

Yet, Strong Towns has repeatedly highlighted that even blighted town cores generate value and tax revenue that far exceeds those of even thriving suburban retail strips. Something is wrong with the whole suburban car-dependent model of development.

In any case, parking policy is again central to many of the problems of traditional neighbourhoods. Here is Charles Marohn again:
... For small businesses -- especially a startup -- providing parking is a huge, expensive burden. When the parking required is excessive to the actual needs of the business, a local government is forcing that business owner to allocate scarce capital to unproductive uses. If you are pro- small business, you are anti- parking minimums.
... And parking minimums force some of the most ridiculous land use decisions I have ever seen. An individual wants to take a vacant storefront and open a business but then city hall tells them they need five parking spots. Where do they get that? Well they either don't (likely) or they buy a neighboring property, tear down whatever is on that lot and convert it to financially unproductive parking. This decimates the tax base when it happens and encourages horizontal expansion when it doesn't. If you are pro- environment or if you advocate for a strong, healthy tax base, you are anti- parking minimums.

I would really like to see more exercises like #BlackFridayParking.  

Do you have an idea for a similar event where you are? Please share!

Tuesday, November 26, 2013

Hong Kong has parking minimums AND very expensive parking. How can that be?

I recently stumbled across some information that resolved a Hong Kong parking mystery. Hooray!

Err. You didn't know there was a mystery about Hong Kong parking? I had better explain.

Singapore and Hong Kong both have big reputations for restraining car ownership and car use.

But there is a puzzle.

Singapore's explicit travel demand management (TDM) efforts are much more severe than Hong Kong's, yet they are apparently less effective.

Hong Kong's car ownership (about 60 cars per 1000 people) is much lower than Singapore's (about 110 cars per 1000) and its public transport mode share much higher. Singapore has around 3 times more private car kilometres of travel per person than Hong Kong. (Thanks Jeff Kenworthy - pdf)

Hong Kong's expensive parking is probably part of the answer to this puzzle.

But why does Hong Kong has such expensive parking?

At those densities, of course parking is expensive, you say? High land prices mean expensive parking, right?

Not so fast. High urban densities DON'T always result in high parking prices.

Just look at Mumbai or Cairo. These cities remind us that parking prices can be low even in dense cities with expensive real-estate.

By contrast, there is no doubt that Hong Kong has expensive parking.

It is not just daytime CBD parking that is expensive. Home-based residential parking is usually also very expensive. Part of that may be property speculation. But even so-called bubble-priced parking is still delivering a yield of about 4 percent so speculation is not the whole story.

Even residential parking in the public housing estates is expensive. For example when I looked in 2009, parking for tenants at Lek Yuen Estate in Sha Tin was HK$1,350 (or more than US$170) per month.

OK.  So maybe Hong Kong restricts parking supply as part of its transit-oriented urban transport strategy? 

Um. No again. Hong Kong actually has surprisingly conventional parking policy. 

That is what we found, to our surprise, in the ADB study that led to 'Parking Policy in Asian Cities'. Hong Kong has conventional minimum parking requirements (and no parking maximums).

The minimums are much lower than in the USA but they are higher than those of Japanese cities or Beijing.

Hong Kong parking requirements are actually similar to Singapore's. But mysteriously, Hong Kong parking is much more expensive than Singapore's.

So we do have a mystery here. 

Why are parking prices so high if Hong Kong parking policy now tries to meet "demand"?

Doesn't the conventional approach to parking, with its minimum parking requirements, always pump too much parking into a city?

Based on Hong Kong, the answer seems to be, no, not necessarily. But why not?

I already had a plausible guess before the recent discovery mentioned above. If we assume parking minimums were absent from Hong Kong before a certain date, then market prices for parking could have risen as car ownership rose without parking construction keeping pace.

This was a hyper-dense city after all with rapidly improving mass transit, so developers might happily build with very little parking, I guessed.

Then at some point, we know that Hong Kong did embark on a conventional approach to parking policy. It would have done so with a context of high parking prices and limited parking supply.

Now consider how Hong Kong would have set the new parking minimums. 

They required estimates of parking demand.

But parking demand in Hong Kong was very low when parking minimums were first imposed. This low demand was shaped by pre-existing high parking prices in highly transit-oriented landscapes, not to mention low car ownership.

It seems that the parking minimums were set rather low, based on that low demand. Even for new areas. The prevailing prices seem to have been taken as a given. So the new parking mandates did not exert (much) downward pressure on prices. (There is a longer story here, for another day.)

In addition, don't forget that parking requirements only apply to new development and redevelopment. So, even with Hong Kong's rapidly changing skyline there are still many 1970s buildings around and any injection of new parking supply is gradual.

And Hong Kong uses some flexibility in applying its parking mandates. There are significant reductions in the most transit-oriented locations. Parking supply can be restricted if the traffic impacts would be excessive. Small-scale street-side retail is usually exempt.

So Hong Kong's shift to a more-or-less conventional parking policy didn't cause low parking prices nor excessive supply (as far as I can tell).

But what parking policies came before the current conventional one? 

Without knowing that, I wasn't as certain of the narrative above as I would have liked.

I had assumed that before parking standards were introduced perhaps there had been a laissez faire approach to parking.

This is where the new information mentioned at the beginning of the article comes in.

Hong Kong actually aggressively restricted residential parking supply in the 1970s. It seems to have had strict maximums (at least for residential development) before it had minimums. 

Parking was a key tool, perhaps THE key tool of that period, aimed at restricting car ownership growth.

I hadn't realized this until I stumbled across this insight (under point 2.5) on a site outlining a 1997 complaint about private residential parking from the Hong Kong Consumer Council.
For traffic control purposes, the declared policy of the Government has been to restrain private car ownership. Prior to 1981, the Government attained this by restricting the provision of residential parking spaces. The Government later adopted fiscal measures to restrict the growth in private car ownership.
And, to confirm, here is the relevant Statement of Intent from the Hong Kong Planning Standards and Guidelines 1992 edition issued by the Planning Department, explaining the switch to a conventional parking policy and the shift away from restricting parking supply:
Parking standards for residential development were formulated in the light of the introduction of fiscal measures to restrict directly the rate of growth in private vehicle ownership and the abandonment of restraint on car ownership by a restriction of residential parking spaces. The overall intention of the standards is to ensure that, except in special cases, future residential developments should have sufficient parking provision to match the current and anticipated car ownership of residents. Generally, therefore, minimum rather than maximum standards are set. This should enable developers to be aware from outset of the extent of parking provision they can plan.  [My emphasis]
So parking supply was deliberately restricted with housing built in 1970s especially and up until 1981. 

And the impact of this would have been large, since there must have been a huge amount of residential construction in the 1970s.

Hong Kong's population rose from 3,995,400 in 1970 to 5,109,812 in 1981. And the 1970s was (mostly) a time of rapid economic growth in Hong Kong. So a large increment of Hong Kong housing took place with very low rates of parking.

I don't have the full story but I suspect that this policy began in the early 1970s. But even before that I imagine that most high-rise housing in Hong Kong was built with little or no parking, since car ownership was tiny in that era.

Why does all this matter? I can think of several reasons. Can you? 

But for now just let me summarize how the points in this post have helped clear up the puzzle about Singapore versus Hong Kong.

As mentioned at the top of this post, it is surprising that although Singapore's car restrictions are more severe than Hong Kong's, car ownership and use in Singapore are much higher.

Part of the answer is Hong Kong's extreme urban density (about 3 times Singapore's) which helps enable excellent public transport service levels.

But Hong Kong's expensive parking must also be important. And I had assumed expensive parking was a result of conscious and current policy in Hong Kong.

But that assumption was shaken by finding that Hong Kong's parking policies today are conventional with parking minimums, and little different from Singapore's. Contemporary parking policy in Hong Kong couldn't explain its high parking prices.

How perplexing.

But now I think I understand how Hong Kong can have parking minimums AND very expensive parking.  Any objections? 

Friday, November 22, 2013

Parking minimums in TODs (part 1)

How much parking should be required in a Transit-Oriented Development (TOD) zone?

And is there a formula related to density or other parameters?

Part of ITDP India's Poster on Transit Oriented Development
These were questions from Mumbai in India a couple of weeks ago, via email and on the Shoupista facebook group.

Zero is the answer I prefer. 

Regular readers will know that I tend to argue for zero parking requirements EVERYWHERE, not just in transit-rich locations. And remember, a zero parking minimum is not a war on cars and does not necessarily mean there will be zero parking.

But YOUR answer to this TOD parking question will depend on your approach (or the approach that you have to work with wherever you are).   

So let's discuss the possibilities, paying special attention to the mindsets on parking behind each approach.

1.  "Right-sizing parking"

The 'conventional suburban' approach to parking fears parking spillover more than it fears excessive parking supply. It sets parking minimums based on peak parking demand at isolated, suburban sites. The result is very high parking requirements.

When applied without exception across the landscape these are a bane of TOD efforts.

So one obvious tweak for Transit Oriented Development zones is to 'Right Size' the parking standards to better match the actual (lower) demand that can be expected in such locations.

Notice something about the mindset here?

This adjustment to parking minimums doesn't question the key assumption of the conventional approach. Every site is still expected to have 'enough' parking.

So this is an approach to TOD zone parking that remains firmly within the conventional parking policy mindset.

This approach requires parking demand investigations for various contexts, including TOD zones.

Examples of such studies that were pointed to in the Shoupistas forum include:
1) A study at UC Davis (led by Dr. Susan Handy) for the California Department of Transportation to develop an adjustment equation for sites in "smart-growth" areas. A user-friendly Excel spreadsheet tool is available from the website. 
2) A study at Portland State University (led by Dr. Kelly Clifton) developed a method to account for differences in trip generation across a range of urban contexts using Portland metropolitan area data.
Do you know of similar efforts elsewhere? Does your city adjust its parking standards to suit TODs?

Something like this seems also to be common in Europe (outside inner-city areas), although with much lower parking demand (and therefore minimums) than in the USA. Examples include Zurich (mentioned in ITDP's European U-Turn report) and Munich.

Again, please notice that this approach to TOD parking is conservative.

It is still in the "conventional" box in the matrix of parking mindsets shown above. It doesn't try to force any change in demand, or even to encourage parking pricing or unbundling. It just tries to avoid forcing too much parking.

So what are the approaches to parking in TOD zones if you have a Parking Management mindset or a Responsive parking mindset?

I will save those for another post.

Tuesday, November 5, 2013

The Unglamorous Secret to Parking Success

This secret is not sexy but it has to be done.

Not that I have anything against sexy. Amazing new technology is opening exciting parking policy horizons. I love the high tech parking innovations that:
  • enable cheap and comprehensive parking space usage monitoring; 
  • make paying for parking easier and lower cost; 
  • reduce cost and practical barriers to the pricing of parking; 
  • reduce enforcement costs, making enforcement less patchy and capricious; 
  • allow the booking of spaces; 
  • enable real-time parking information for users; and 
  • allow operators to optimise prices and management. 

But this post is about something more FUNDAMENTAL, something every city needs BEFORE getting too excited about technology.


Effective On-Street Parking Management is the Secret Key to Parking Success 

It is not really a 'secret' of course. But many jurisdictions do their best to ignore the obvious.

And I don't really blame them.

Getting 'good enough' control of on-street parking seems like mundane stuff. It can be politically painful. The many winners hardly thank you but the much less numerous losers complain loudly and bitterly. Success usually requires reforming hide-bound institutions. It lacks ribbons for politicians to cut. The results can take time.

Most on-street parking in Mumbai is free-of-charge and almost unmanaged. 
But there is no escaping the need to knuckle down and get it done. Every city needs to establish at least the basics of effective on-street parking management.

I was in Mumbai recently, and this was a key theme that came up over and over.

Crisis is beginning to open eyes in Mumbai I think.

But in too many cities on every continent local leaders hope to avoid tackling the thorny challenge of on-street parking.

They hope that requiring lots of off-street parking will help. They hope that building public parking structures will cure their parking problems.

Unfortunately, it doesn't work. You have to tackle on-street parking!

Creating off-street parking is a slow and expensive business. And off-street parking does not magically vacuum parking off the streets.

All over the world, we find case after case of underutilized off-street parking next to chaotic and saturated parking in the streets.

If the on-street parking remains unmanaged then it will remain chaotic, whether there is off-street parking nearby or not.

The only way to fix on-street parking problems is on-street parking management.

Actually, I am exaggerating slightly. Focusing on off-street parking supply CAN work in certain cases.

What cases?

If a city follows the American suburban example and spends decades applying car-oriented guidelines ruthlessly to every aspect of transport and urban planning, while also investing massively in roads, and is lucky enough to also have robust economic growth throughout those decades, then perhaps off-street supply can solve its parking problem.

But is this 'cure' worse than the disease? If you follow that path, you will end up with sprawling automobile dependent metropolitan areas and inner cities that have hollowed out to make way for parking. You may have solved your parking problem but is that really your vision for your city?

And is following a totally car-dependent path really even an option for most cities?

So for most cities with on-street chaos, the answer is to focus first on on-street management.

Even if you really really think you need off-street supply, focus FIRST on getting control of on-street parking.

On-street pricing improves the willingness to pay for off-street parking. So efficient parking management on the streets will actually make your off-street parking facilities more financially viable.

Information gleaned from on-street management will also help you to make these investments in the right places.

Efficient on-street pricing can easily nudge long-stay employee parking towards off-street parking options or towards parking on less overburdened streets. Since these vehicles are there all day, moving them away from problem streets makes a huge difference.

So, even if you are convinced you need more parking, please make on-street parking management your FIRST step, before adding to parking capacity.

What does it take to achieve the unglamorous secret? 

At the very least, these steps are important:

  • Establish clear rules and communicate with clarity where and when parking is legal or illegal
  • Build enforcement capacity (with supporting institutions)
  • Establish a trustworthy system for levying parking fees per unit of time (per minute or per hour for example)
  • Establish at least basic parking data collection capacities (initially very simple inventory and occupancy surveys for problem areas are enough, with duration surveys if possible)


Please share YOUR stories of local governments biting the bullet and tackling on-street parking chaos!

Monday, October 7, 2013

Is 30% of traffic actually searching for parking?

San Francisco Examiner headline asked that question recently.  (Hat tip Parking Today blog)

Should you care if you are not in San Francisco? Yes! That motorists searching for parking can add greatly to congestion is a very widely used argument for improved on-street parking management, especially performance pricing.

To be precise, the Examiner article questions "the statistic that 30 percent of all congestion in the City is caused by frustrated drivers circling the block for that elusive parking space."

Err. Thirty percent of traffic is not the same as thirty percent of congestion.

But, either way, does the SF Examiner article have a good point? Is this a gotcha moment for that 30% thing?

Wait a minute! Let's take a step back first.

My first reaction upon skimming the article was to say the article is holding up a straw man to easily knock him down.

Is anyone really claiming 30% of urban congestion (or traffic) is cruising for parking? 

Not me. Not Donald Shoup.

How much of this traffic (in Seoul in this case) is actually searching for parking?

Donald Shoup is the original source of this "30% of traffic" talk. Did he claim that 30 percent of congestion is due to parking search traffic?  Not exactly. Here he is in 2011:
Sixteen studies conducted between 1927 and 2001 found that, on average, 30 percent of the cars in congested downtown traffic were cruising for parking.  [my emphasis]

I can see how this morphed into a more general claim. But notice that he qualifies the "30% of traffic" with "of congested downtown traffic".

Why did he do that? Because the studies he is citing have that specific focus.

They can't and don't claim to measure the share of ALL traffic or all congestion that arises from parking search. As Shoup says in Chapter 11 of his magnum opus on parking policy reform, The High Cost of Free Parking (p.291):
The studies are selective because researchers study cruising where they expect to find it - on streets where curb parking is under-priced and overcrowded. 

From the sixteen studies, there were six measurements of the percentage of traffic that is seeking parking. The results ranged from 8 to 74%, for that average of 30%.   [By the way, thirteen of the studies generated another number that highlights the cumulative costs of cruising for parking, the average time spent by each motorist on the parking search (an average of 8.1 minutes in case you were wondering). Some studies yielded both numbers.]

All six estimates were from major business districts in urban cores:
  • Detroit, USA 1927 A:  DOWNTOWN location between 2 and 6 pm (presumably on a weekday). Found 22% of traffic was 'cruising for parking').
  • Detroit 1927 B:  DOWNTOWN location between 2 and 6 pm. Found 34% as cruising percentage.
  • New Haven, USA 1960: CBDs of New Haven and Waterbury, Connecticut, with three study times (quiet summer period, average November period, and pre-Christman rush period). Calculated that at least 17% of CBD traffic was parking search traffic. 
  • Freiburg, Germany 1977: CENTRAL Freiburg, with 74% of 800 tracked cars estimated to be searching for parking. 
  • Cambridge, Mass., USA 1985: Harvard Square BUSINESS DISTRICT, 10 am to 3:30pm (hence covering the lunch peak), estimating that 30% of cars were cruising fro parking. 
  • New York, USA 1993: MID-TOWN, West Side, 8-10am and 11am-2pm, finding 8% of traffic was searching for parking. 

The point of all of this is NOT the 30% average! 

The point is to highlight that, parking search traffic is potentially a very big deal in CERTAIN IMPORTANT CIRCUMSTANCES.  

What circumstances? When on-street parking is badly managed and saturated, so that we get lots of search traffic (and waiting and double parking too).

That is how I have always understood the talk about parking search traffic being a significant percentage of traffic.

Shoup himself was cautious in the book about making too much of the specific numbers from the studies he cites (p.291):
But these studies dating back to 1927 are mainly of historical interest. The data were probably not very accurate when they were collected, and the results depended on the time of day, the specific place, and the season when the observations were made. 

Nevertheless, these studies do show that parking search is potentially an enormous source of congestion and unnecessary traffic in busy business districts when on-street parking is mismanaged so that it is often totally full.

As Shoup goes on to say (p.291):
But because curb parking is underpriced and overcrowded in the busiest parts of most of the world's big cities, the sun never sets on cruising. 

More recent investigations in New York City commissioned by Transportation Alternatives confirmed that parking search CAN be a huge share of traffic in busy areas. 

In 2006, on Prince Street in Soho (pdf) on Tuesday, Friday and Saturday afternoons/evenings, they found an average of 28% of intercepted motorists (at traffic lights) were looking for parking in the area. On Saturdays the share was 41%!

In 2007, in Park Slope, Brooklyn (pdf), they looked at four periods (weekday peak, two weekday moderate times, and weekend peak) and found overall 45% of traffic was cruising for parking.

So, like the studies cited by Shoup, both of these NYC studies focused on problem places at problem times.

We can't extrapolate to a general claim about shares of traffic. But again they highlight how extreme parking search traffic CAN BE.

But let's get back to the San Francisco Examiner. Does the article have a good point or not?

Sadly, maybe it does. I thought it was bashing a straw man, but no.

There really has been some fast and loose talk about the 30 percent thing.

It was challenging SFPark claims in particular. So I looked for some and found this:
“Circling for parking accounts for approximately 30 percent of San Francisco’s congestion,” said Tom Nolan, Chairman of the SFMTA Board of Directors. 

SFPark is San Francisco's Performance Pricing trial. It has not been as controversial as many expected. Nevertheless, questioning a key SFPark claim makes good news copy.

SFPark said the claim was based on Donald Shoup's book. There hasn't been a specific study of this in San Francisco.

So I have to agree that it is a misleading claim.

What is true is that, based on the Shoup-cited studies, parking search is very likely to account for a lot of San Francisco congestion.

But no-one currently knows how much of San Francisco's congestion (or traffic) arises from cruising for parking.

Sorry SFPark. 

And I gather SFPark is not alone. Various others may have been getting a bit too attached to that specific 30% statistic, taking it as gospel, and using it in sloppy ways.

By the way, it is easy to see how this happens. Quoted statistics, especially startling ones like this, tend to harden with time and distance from their origins.

Donald Shoup's statement that parking search traffic was found in certain studies "to be on average 30% of congested downtown traffic" or my statement in a recent presentation, that parking search traffic is "often 30% or more" could easily become misleading if quoted beyond their original contexts discussing situations with badly mismanaged on-street parking.

And with repeated mentions of that 30% figure, it seems to have morphed into a misleadingly precise and general claim about the percentage of overall traffic or congestion being due to parking search. And then, even more misleadingly, it was then claimed to apply to a specific place again, like San Francisco. Oops.

What is the bottom line here?

It would be annoying if debunking the sloppy use of this 30% average undermines the important point that:
cruising for parking CAN cause a huge mess in busy areas, at busy times, when parking is mismanaged. 

This point is still valid and not undermined by the discussion above. Parking saturation certainly causes traffic congestion (and other problems).

How much exactly? Well, it depends. Do your own little study in the context you are interested in.

But potentially it is a LOT.  Much more than was widely realized before Donald Shoup came along.

Pity about that 30 percent figure, though.