Infrastruktur og pendling for fremtiden

The mighty TGV at Zurich HB

Jeg har tidligere skrevet endel om hva jeg synes om pendling. Jeg hater det, og mener det er skadelig for samfunnet, arbeidstakere, familier, arbeidsgivere og miljøet. Derfor bør det begrenses.

Men vi er avhengig av at mange pendler. Derfor må vi også bygge ut infrastruktur slik at skadene blir minst mulig. Sanjoy Mahajan hos Freakonomics peker på noe banalt, men også viktig i denne debatten. Han ville estimere hva som er mest effektivt av å utvide en motorvei med et ekstra felt, eller bygge en toglinje (mine uthevinger).

I’ll first estimate the carrying capacity of one lane of highway; it is the number of passengers who pass by during a fixed time (usually 1 hour). For this estimate, a lesson from driver-education classes is helpful. Driving courses teach, and many drivers-license exams test, the 2-second following rule:

Each car should leave a distance between it and the next car equal to 2 seconds of travel time.

If the drivers follow this rule, a single lane of highway carries one car every 2 seconds (no matter how fast the traffic is flowing!). Each car carries roughly 1 person, making for a flow of 1 person every 2 seconds. With 3600 seconds in 1 hour, a single lane of highway carries:

1 person per 2 seconds
* 3600 seconds per hour
= 1800 people per hour

These figures are all rough anyway, so let’s call it 2000 people per hour. This estimate is one apple in the comparison.

The other apple is the carrying capacity of a train line. To make a fair comparison, I’ll compare highly developed roads to a highly developed train system: say a French, Swiss, or German train. (About the American train system, my mother taught me that if you cannot say something nice, don’t say anything.)

One train car may hold about 150 people. The whole train may contain 20 cars. And on a busy train route, one train might run every 5 minutes or 12 times per hour. Therefore the capacity of the train line is estimated with the following product:

150 people per carriage
* 20 cars per train
* 12 trains per hour
= 36,000 people per hour

These figures are also rough, so let’s call it 40,000 people per hour. (Even though the individual factors are highly variable, the final estimate is reasonable. According to the figures at this commuting blog, one track of the highly optimized Parisian commuter-rail system, the RER, can carry 55,000 passengers per hour. And Caro himself quotes “40,000 persons per hour” for a single lane of rapid transit.)

This capacity is 20 times the capacity of a highway lane! Even allowing that a train track could be wider than a highway lane, one train line could replace an entire highway, even a highway with five lanes in each direction.

Dette fikk meg til å tenke på utvidelsen av E18 fra Oslo vestover mot Asker og Drammen. Her er kapasiteten sprengt og det er håpløs kø i begge retninger hver dag. En oppgradering av de kilometrene som går gjennom Bærum er anslått til å koste 10 milliard kroner (jeg vet ikke hvor langt det er, men la oss si 10 kilometer). En oppgradering til dobbeltsporet toglinjer for lyntog er anslått til 23 milliard. Helt til Skien! Og for tilsammen 40 milliard får man oppgradert Østfoldbanen Oslo – Halden også.

(Bilde av Julian Gajewski med CC-by-nc-sa-lisens)

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