Aaron S. Hawley (aaronhawley) wrote,

Prius saves gas money? (follow-up)

Toyota makes the Prius -- a popular hybrid car that gets around 50 miles to the gallon (21 km/L, 4.7L/100km). Presumably, these vehicles save you money at the fuel pump. However, their sticker price is seemingly high. One way to check the economic argument is to compare its total cost with a similar but non-hybrid conventional car and see when driving a hybrid starts saving you money. A convenient and fair comparison is the Corolla also made by Toyota.

Almost 5 years ago, Bill McGonigle compared a Prius with a Corolla and found that only after driving 280613 miles (451603 km) will you start saving money. I confirmed his math with some simple Lisp programming. Has this result changed?

Five years later, the price of gas is up to 4 dollars (US) from 3 dollars but the price point for a Prius is higher. You still need to drive 229354 (369109 km) miles before you start saving gas money. That's 60000 miles (96560 km) less than 5 years ago. Here's the arithmetic in the Emacs Lisp programming language.

(let ((gas-price 4.0)         ;; dollars/gallon
      (prius-price 24000.0)   ;; US dollars
      (corolla-price 16130.0) ;; US dollars
      (prius-mileage 48.0)    ;; miles/gallon
      (corolla-mileage 34.0)) ;; miles/gallon
  (/
   (* prius-mileage corolla-mileage
      (/ (- prius-price corolla-price) gas-price))
   (- prius-mileage corolla-mileage)))

Toyota has introduced a new c model of the Prius this year. A smaller-sized version, it is tuned to get better mileage in the city -- better than it does for highway driving. It's also 15% cheaper than the regular Prius. If you compared a city-driving Corolla with the Prius c you'd only have to drive 38802 miles (62446 km). That's pretty good, but is it a fair comparison? Here's that arithmetic before I answer that question.

(let ((gas-price 4.0)         ;; dollars/gallon
      (priusc-price 18950.0)  ;; US dollars
      (corolla-price 16130.0) ;; US dollars
      (priusc-mileage 53.0)   ;; miles/gallon
      (corolla-mileage 27.0)) ;; miles/gallon
  (/
   (* priusc-mileage corolla-mileage
      (/ (- priusc-price corolla-price) gas-price))
   (- priusc-mileage corolla-mileage)))

Average drivers don't earn 15000 miles (24140 km) a year in the city. Most of those miles are at a highway's pace. Further, the smaller Prius c is more comparable to the Toyota Yaris than a Corolla. Comparing the lower sticker price and highway mileage of a Yaris with the Prius c driven on the highway requires driving 264112 miles (425047 km). Here's the arithmetic.

(let ((gas-price 4.0)         ;; dollars/gallon
      (priusc-price 18950.0)  ;; US dollars
      (yaris-price 14115.0)   ;; US dollars
      (priusc-mileage 46.0)   ;; miles/gallon
      (yaris-mileage 38.0))   ;; miles/gallon
  (/
   (* priusc-mileage yaris-mileage
      (/ (- priusc-price yaris-price) gas-price))
   (- priusc-mileage yaris-mileage)))

After 5 years, the hybrid car still isn't economical unless a typical owner drives one for 15 years. According to Consumer Reports, Toyota's reputation for reliability is extending to the Prius, where a Prius is able to maintain its efficiency and the batteries have held up after 10 years. However, the average Prius owner probably doesn't hold on to the car this long.

More likely, consumers purchase hybrid vehicles because of their reduced environmental impact. It's estimated that just producing a car can be 10 to 20% of a vehicle's lifetime emissions. Presumably, the energy to make a Prius is greater than a conventional car since it has two engines (combustion and electrical) and additional battery. However, Toyota doesn't release the estimated emissions from manufacturing a Prius.

The city-optimized Prius c is a triple threat in metropolitan areas for its lower price, better efficiency and reduce impact on smog. However, these places typically have mass transit. The best way to save money is commute by walking, biking, car pooling or taking the bus or train. These options are better for the environment as well.

Tags: ecology, emacs, programming
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