US-19, Marchetti’s Law, Jevon’s Paradox

I left the CNU conference with a head full of information, reams of notes, and one incredible insight to the mess here in North Pinellas. Everybody stuck in a traffic jam on US-19 or McMullen Booth wants to “Add a lane”. Most of us know this never works, due to “Induced demand”. But I learned this failure is universal and was understood 30 to 150 years ago.

One Hour … & Thirteen Per Cent

Marchetti-2In 1994 Italian physicist & social scientist Cesare Marchetti, published a universal “Constant” for man’s budget and time allotted his daily travel, turns out since the beginning of time. This concept was first published years previously by an obscure US transportation engineer, Yacov Zahavi, from data collected in the 50s and 60s, and was even casually observed by Bertrand Russell in the 1930’s. And “Marchetti’s Constant” has been continually confirmed, including recently using real-time cell phone data. Go search on “Marchetti’s Law” … and stand back.

The empirical conclusion reached by Zahavi is that all over the world the mean exposure time for man is around one hour per day. … Even people in prison for a life sentence, having nothing to do and nowhere to go, walk around for one hour a day. … People spend about 13% of their disposable income on traveling. The percentage is the same in Germany or Canada, now or in 1930. Within this budget, time and money are allocated between the various modes of transport available to the traveler in such a way as to maximize mean speed. The very poor man walks and makes 5 km/day, the very rich man flies and makes 500 km/day. The rest sit in between.

– Anthropological Variants in Travel Behavior, C Marchetti, 1994

Marchetti cited in his paper ancient Greek villages, early European cities, post war suburban sprawl (and prisoners).

Paradox: Conservation Increases Consumption

In 1865, the English economist William Stanley Jevons was trying to explain how attempts at conservation of a resource, through technology & innovation, actually leads a large system (society) to increase its aggregate use. Jevons-2“Jevon’s Paradox” is confounding. When cars got 10 MPG, people could only afford to drive to work, maybe a small joyride on Saturday. As cars became more efficient (to mandate “saving America’s aggregate oil reserves”), each individual driver now found himself with a car getting 15 mpg, 20, 30, 40mpg. To the individual: just hop in my car for dinner across town, take a day long drive to some distant relative? Suddenly, due to governmental intervention, the individual perceives gas as “cheap”.

In aggregate, total fuel consumption goes up. With conservation technology, the “Reserves” actually drain faster. “Jevon’s Paradox” was addressing English coal, a scarce resource before America’s civil war, but it applies to gasoline, drinking water, forests … and highway lanes. Whatever savings provided in aggregate, by government or by innovation, unless otherwise prevented from individual folly, is immediately consumed, plus more.

What would offset those huge fuel efficiencies? Only an increased cost, as perceived by the individual. While MPG went from 8 to over 40, the price per gallon also went from 25 cents to over 3 dollars. Of course, at the same time wages, inflation, livings costs, real estate scaled to various values at various rates at various time. Each consumer, at any time, perceived themselves “rich” or “poor”, and either conserved, or splurged, based on their individual perception.

I personally remember a wave of tiny Japanese imports in the 1980s, as Detroit raced to ditch 4 door guzzlers for tiny models. This was then followed by big SUV’s and pick-up trucks throughout the 2000s, you couldn’t give away a small car. It was all about the individual’s perception.

Had American leaders been truly concerned about “strategic fuel reserves” there would have been taxes and rations, but any such talk resulted in immediate election losses. That would require ration “stamps”, limiting use despite the individual perceived “wealth” and “abundance”, while still providing unlimited fuel for commerce. Instead we had Hummers declared tax free personal vehicles and “Drill, Baby, Drill”. Remember?

Today, as millennials (and elderly) cannot afford rent, food, and healthcare, many forego cars, using daily rental cars when needed, or eliminate the once standard second car by choosing where they live. We see transit, bikes, even walking to work skyrocketing for a significant minority of younger Americans.


Highway lanes follow both Marchetti and Javan’s laws. You cannot provide more and expect less use (without restrictions). I personally think Marchetti & Zahavi underestimated America’s independent streak; it is probably 45 minutes or an hour before American’s would think of moving closer to work. Some car centric Americans even boast about a drive of 60 to 90 minutes or more for “country living”. Those that take a train or bus easily tolerate commutes of more than 30 minutes. But whether driving to work, the doctor, the mall, or to attend a meeting; after 30 minutes most Americans (it turns out humanity) start to ask “Is this trip necessary?” When invited back to another potluck or poker night, they find themselves making excuses … or car pooling with a friend. Turns out, its  universal, and since time began.

jam_laneWhen US-19 was 2 lanes, people could commute from St Pete up to Tarpon, in 30 minutes. Eventually, with new stoplights Marchetti’s Law had drivers demand more lanes. The bayside bridge was built, and what we got was East Lake Woodlands then Lansbrook, unthinkable construction without those widened roads … then more jams. We widened Hillsboro Rd, Curlew, Tampa, Keystone, and for that effort we developed every single lot between Gulf-to-Bay and the Pasco line … then more jams.

Drivers demanded a third lane for US-19 and suddenly south Pasco had new subdivisions up in Trinity, Port Richey, all of them Marchetti’s 30 minutes away. Add a fourth lane and buildings sprouted as far north as Spring Hill and Weeki Wachee … yet McMullen Booth is still a parking lot every morning and evening rush hour. US-19 now is now limited access, with overpasses and ramps, every day has tie ups. But subdivisions now stand even in Hernando country.

It Just Doesn’t Work

No matter how many lanes you add, what new technology, individual drivers will simply “perceive” new distant places to be within their “Marchetti Constant”. They buy new houses, newly built in new distant subdivisions. Innovation, whether an extra lane, a bypass road, computer timed lights, or a billion dollars for limited access flyovers just fill distant pastures with new homes. Developers laugh all the way to the bank, and drivers still sit in Pinellas traffic.

McM_Map2Now FDOT is building a freeway connector from I-275 through PIE airport, dumping car volume onto both McMullen and US-19 (even though both already jam). This will only encourage more Pasco development, just as the Veterans toll road did in Hillsboro. None of that construction lets you drive faster or arrive earlier; it only provides a temporary perception that living farther away, buying newly built houses in now rural fields, lies within “Marchetti’s Constant”. The FDOT next project, already on the drawing board, will be for miles long flying roads, like the LeRoy Selman through South Tampa, either sailing above McMullen Booth or US-19. It will have 4 additional lanes (toll, of course) running only southbound in the morning northbound in the evening. It will cost BILLIONS of dollars to build, be ugly as sin, and destroy Pinellas property values. And it will not relieve Pinellas traffic congestion one iota. But only make even farther locations available for development and profiteering.

The Future

Alternatively, people with local jobs could live closer to where they work. People could use transit, decreasing traffic. Such increased ridership leads to increased quality and quantity from scale. Or, as drivers “demand”, we can build another lane, a decked bridge, or give everybody helicopters and rocket ships, and they will just live farther away. But remember this, the next generation of kids are not interested in buying those distant homes, they won’t have cars to get there, and they can’t afford the gas even if they did. You are building failure.

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