Key Vocabulary (appropriate for a word wall):
mass transportation, BTU (British thermal unit), passenger mile, energy intensity
Resources from other Web sites:
http://cta.ornl.gov/data/Index.shtml – Transportation Energy Data Book from the Oak Ridge National Laboratory (Tables 2.12, 2.13, and 2.14 are also available at end of this lesson)
Classroom Discussion:
In the discussion about reducing greenhouse gas emissions from vehicles, you will also need to consider mass transportation options when developing your greenhouse‐gas‐reduction action plans.
In Lesson 4, you will use data to analyze the fuel efficiency of mass transit options.
Until now, we have focused on ways to reduce fuel use and emissions using privately owned vehicles. Another set of options is for people to use mass transit. The many forms of mass transit generally serve different needs. Buses travel distances of several city blocks to several hundred miles. Trains usually operate between cities or sections of cities, while passenger airplanes operate exclusively between cities. Mass transit can be more efficient because more people can use a vehicle at one time.
Most cars or light trucks hold only four to six people, while buses can hold more than fifty, and planes and trains can carry hundreds. Additionally, mass transit vehicles themselves can use many of the same alternative energy technologies that are used to make privately owned vehicles more efficient. Statisticians measure efficiency in several ways. One is to consider the amount of fuel needed to travel one mile. Another—energy per passenger mile—considers how many people are using a vehicle, making comparisons between cars and mass transit easier. This is referred to as energy intensity.
It is important to understand that there are many forms of engineering. Vehicle design is an important one in a society where the majority of people use individual vehicles as their primary transportation. But engineers also design mass transit systems and plan urban environments with transportation issues being a primary concern. Design and construction of these systems requires an understanding of the options available to people as far as how they get from one place to another. A poorly designed mass transit system is no better than none at all, since people will use other options. An urban area can be designed to encourage people to use mass transit, rather than individual vehicles.
Whether people decide to use single vehicles, carpool, rideshare or take mass transit is based on many factors. Students in this lesson will learn about some of the factors in order to better understand what positive changes they may be able to build into their action plans.
As a reminder, at the end of this module, you will be asked to create an action plan for reducing greenhouse gas emissions produced by transportation usage in their community. The final project will be completed by you and your team.
Let’s review the concepts from the previous two lessons by reading the following statements aloud where you will give me a thumbs‐up if the behavior raises fuel efficiency, thumbs down if it does not.
Quick starts (decreases efficiency)
Driving a lighter car (increases efficiency)
Adding more electronics (decreases efficiency)
Adding more passengers (increases efficiency)
Please record in your Engineering Notebooks the new units of measure you are about to introduce.
There are many types of engineers. Some design vehicles, some design buildings, still others design transportation systems such as highways and rail lines. Some are city engineers who design ways of controlling how transportation moves through a city or town.
We have already discussed the British thermal unit (BTU). Since energy can come in many forms (light, heat or thermal, electrical, etc.) that many years ago, scientists and engineers agreed on a unit to which all measures of energy can be converted for comparison. (You may also wish to write on the board “one BTU = one British thermal unit = 1,055 joules”.
For the purpose of this lesson, we will be working with BTUs. So, one gallon of gasoline, when burned, releases about 123,000 BTUs (130,000,000 joules).
Because the vehicles we are considering can use many forms of energy, this unit will be very useful for us in comparing efficiency of those vehicles.
Knowing how much energy a gallon of gasoline releases, we can calculate how much energy (in BTUs) is used per mile and per person. The measure is called a passenger mile: how much energy it takes to move a person one mile.
Student Activity 12:
Let’s look at the following:
6,904 BTUs/passenger mile
4,235 BTUs/passenger mile
One figure on the board represents an average bus in the United States in 2006 and the other represents a light truck, such as a pickup truck or an SUV, in that same year.
Let’s guess which is which and offer an explanation and record your choice and reasoning in your Engineering Notebooks.
Some give me your explanation and reasoning (e.g What makes you think so? Why would that be true?)
Reveal or confirm that the larger of the two numbers represents the truck. You will likely see that, while buses may be far less efficient than trucks, they also hold many more people. On balance, this means that buses are more efficient as long as they can attract enough riders.
Student Activity 13:
You will explore online the Oak Ridge National Laboratory Transportation Energy Data Book in order to find out more about the energy use profiles of several types of vehicles. The Data Book is a rich, but dense, source of material. How much guidance you give to your students should depend on the skill of the students in analyzing Internet documents and interpreting data tables.
To begin this discussion, I want you to discuss whether using an SUV can be more efficient than using a hybrid car. Of course, in any one‐to‐one comparison it cannot—even hybrid SUVs have a worse fuel economy than a hybrid car due to their vehicle mass and aerodynamics.
In your discussion, consider the case where six people each drive to work in a hybrid car while six others commute in one SUV. Ask which use is more efficient. Use this question to lead into a discussion of other multi‐passenger vehicles, such as buses, planes, and trains.
You will use the tables found online at the Oak Ridge National Laboratory at http://cta.ornl.gov/data/Index.shtml to investigate the efficiency of various modes of transportation. In particular, you should focus on Chapter 2 – “Energy.” In particular they will look at data on tables 2.12, 2.13, and 2.14 (found at the end of this lesson if print copies are needed), although the data in other chapters may be useful for their final module project.
Get into your teams and use “Chapter 2 – Energy” to find the energy intensity of buses, trains, airplanes, and automobiles. First, use Table 2.12 – “Passenger Travel and Energy Use” to calculate how many miles per gallon of gasoline‐equivalent energy the average train, bus, and plane uses.
The tables used in this section can be tough to interpret, so don’t be shy and ask if you have any questions.
For example, Table 2.12 lists several types of passenger vehicles, and some have subsets. The table then goes on to list the number of each type of vehicle and the cumulative number of miles driven by those vehicles (vehicle miles).
The next column is passenger miles. This is vehicle miles divided by the number of passengers in those vehicles. The number of passengers per vehicle is the load factor, which is the next column. The final three columns are energy intensity.
The last column is the total energy, in BTUs, used by each class of vehicle. The second to last column is the energy use divided by the number of passenger miles, and the column labeled “BTU per vehicle mile” is the energy use divided by the number of vehicle miles.
Create a spreadsheet program to create a bar graph representing the BTU/vehicle mile for each of these four types of transportation. Each group should take this data from Table 2.13 and Table 2.14, and then create a line graph showing how energy intensity per passenger mile has changed for cars, buses, trains, and planes since 1970.
You should use a spreadsheet to perform this task. If not, then allow students to graph the data at five‐year intervals to save time.
Print out graphs or sketch their graphs in their Engineering Notebooks.
Classroom Discussion:
You may be surprised to see data that shows buses have an average of 8.8 riders at a time. Ask students to calculate how many people a bus would need to carry to make the vehicle as fuel efficient as a car.
An important thing to note about buses is that over the last twenty‐five years, many city bus systems have begun to use natural gas and other alternative fuels. While the BTUs of energy consumed may be greater, the greenhouse gas emissions are reduced when this type of fuel is burned. Note the disclaimer at the top of the charts that explains that this data is very general and that it does not differentiate for the type of fuel used by buses. Even so, at present the percentage of buses using gasoline is still greater than those using alternative fuels.
Let’s discuss the changes in mass transit usage since 1970. Refer to Table 2.13. Have the number of passengers or the fuel economy of buses decreased from 1970 to the present? Using the chart, you can surmise that it is both. BTUs per vehicle mile increased, which indicates decreased fuel economy. However, BTUs per passenger mile increased by a much greater percentage, indicating that fewer people were riding buses.
Let’s discuss the changes in other modes of transportation shown on Tables 2.13 and 2.14. The results indicate that all other modes of transportation are more efficient per passenger mile
Note: Table 2.13 is less complicated than Table 2.12. The rows are years, and the columns represent the BTUs per vehicle mile, or BTUs per passenger mile for a given type of vehicle. Table 2.14 is similar, but expands this to include air and rail vehicles.
One of the most important elements of any decision to build more mass transit is location. For mass transit to be beneficial, it must be accessible to the people who need to use it, and it must go to places that people would like to go to, such as schools, job centers, shops, entertainment, or tourist attractions.
Please identify the nearest bus or train station to their home or school (or use the Internet to find this information). In rural schools, you may wish to consider long‐distance travel options such as rail or bus lines or air travel options. You should use a search engine to find you local mass transportation department, which should have a map of the local transit systems.
Another consideration in mass‐transit decisions is population density. Transit planners calculate that buses are only efficient in an area with a population density higher than 3,000 people per square mile. Research online to find the population density of your zip code.
Is the density high enough to support an efficient mass transportation system?
If there is a variety of local mass transportation options in your area, which options do you use when you travel. Lead a discussion of the reasons that people might or might not decide to use mass transportation. Record some of these thoughts in you notebooks.
Student Activity 14:
Let’s discuss within your teams and then propose a response to this question:
There are at least two ways to reduce vehicle energy intensity or energy per passenger mile. What are they?
Please write a short essay within your journal, describing one improvement that could be made to the local mass‐transit system. If there is no mass‐transit system in your area, you can feel free to argue either why one should be created, or why it would not save energy to use mass transportation in your area. If your school is in a low‐density population area, you may also wish to focus them on long‐distance use of mass transportation.
Classroom Discussion:
Briefly review the pros and cons of mass transportation and what their recommendations are for reducing the BTUs per passenger mile.
Remind them that today you learned about mass transportation options. In Lesson 5, you will explore something called incentives that government and many businesses use to change people’s transportation behavior and decrease the use of fossil fuels.