A metropolitan region generates 7.5 billion passenger · km of transportation demand per year and is experiencing 2% per annum growth in total passenger · km, and a 0.5% decline in energy intensity of passenger ·km. Current energy intensity of automobile travel and public transportation is 2200 kJ

Question

A metropolitan region generates 7.5 billion passenger · km of transportation demand per year and is experiencing 2% per annum growth in total passenger · km, and a 0.5% decline in energy intensity of passenger ·km. Current energy intensity of automobile travel and public transportation is 2200 kJ/passenger ·km and 1000 kJ/passenger· km, respectively, and share of passenger · km is 90% and 10%, respectively, for those two modes. For the purposes of this example, ignore all other types of transportation. Suppose the government institutes a comprehensive transportation program that increases the passenger ·km share for public transportation by 5 percentage points over 10 years.

Calculate (a) the baseline energy consumption in the present year, (b) the baseline energy consumption after 10 years, and (c) the reduction in energy consumption in the 10th year relative to the baseline in that year due to the policy.

Accepted Answer

(a) For the current year, the total energy consumption is the sum of the consumption for the two modes, as follows:

[latex] ext { For car: }\left(7.5 imes 10^{9} \mathrm{pkm} ight)(0.9)\left(2200 \frac{\mathrm{kJ}}{\mathrm{pkm}} ight)\left(10^{-12} \frac{\mathrm{PJ}}{\mathrm{kJ}} ight)=14.85 \mathrm{PJ}[/latex]

[latex] ext { For public trans.: }\left(7.5 imes 10^{9} \mathrm{pkm} ight)(0.1)\left(1000 \frac{\mathrm{kJ}}{\mathrm{pkm}} ight)\left(10^{-12} \frac{\mathrm{PJ}}{\mathrm{kJ}} ight)=0.75 \mathrm{PJ}[/latex]

The sum of these two values is 15.6 PJ.

(b) For the 10th year, we account for the growth in passenger·km as follows:

(7.5 × 10[latex]^{9}[/latex] pkm)(1 + 0.02)[latex]^{10} [/latex]= 9.14 × 109 pkm

Modal energy intensities have also changed, and these are recalculated as

[latex] ext { For car: }\left(2200 \frac{\mathrm{kJ}}{\mathrm{pkm}} ight)(1-0.005)^{10}=2092 \frac{\mathrm{kJ}}{\mathrm{pkm}}[/latex]

[latex] ext { For plublic trans.: }\left(1000 \frac{\mathrm{kJ}}{\mathrm{pkm}} ight)(1-0.005)^{10}=951 \frac{\mathrm{kJ}}{\mathrm{pkm}}[/latex]

Recalculating the energy consumption by repeating the calculation in part (a) with the increased number of passenger ·km and reduced energy intensity gives 17.22 PJ for car, 0.87 PJ for public transport, and a total value of 17.22 + 0.87 = 18.09 PJ for the entire system

(c) This alternative assumes that in the 10th year the modal split is 85% car / 15% public transport.

We can therefore recalculate as in part (a) using the new values:

[latex] ext { For car: }\left(9.14 imes 10^{9} \mathrm{pkm} ight)(0.85)\left(2092 \frac{\mathrm{kJ}}{\mathrm{pkm}} ight)\left(10^{-12} \frac{\mathrm{PJ}}{\mathrm{kJ}} ight)=16.26 \mathrm{PJ}[/latex]

[latex] ext { For public trans.: }\left(9.14 imes 10^{9} \mathrm{pkm} ight)(0.15)\left(951 \frac{\mathrm{kJ}}{\mathrm{pkm}} ight)\left(10^{-12} \frac{\mathrm{PJ}}{\mathrm{kJ}} ight)=1.30 \mathrm{PJ}[/latex]

The combined total is 17.56 PJ. Therefore, the energy reduction is 18.09 − 17.56 = 0.52 PJ.

Discussion The results of this example show the challenge of curbing growth in transportation energy consumption in the face of continually expanding passenger · km values. Despite a 50% increase in the amount of public transportation over 10 years, energy consumption is higher in year 10 than it is in the current year. Nevertheless, public transportation has made a measurable reduction in energy use of 0.52 PJ, which is equivalent to 21% of the 2.49 PJ growth in energy use that occurs with no increase in public transportation.

Question 14.1: A metropolitan region generates 7.5 billion passenger · km o...

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