Transportation Energy Savings

The next frontier of home energy savings is in the garage.

October 03, 2017
Winter 2017
A version of this article appears in the Winter 2017 issue of Home Energy Magazine.
Click here to read more articles about Archive

As a home energy auditor, I looked at dozens of garages but never considered how much my clients could save by changing their transportation habits. In 2012, I worked for a small nonprofit that offered residential and commercial energy audits in Michigan. That spring, after my office moved to downtown Ann Arbor, I started occasionally commuting by bicycle. Four years later we sold our second car, and we haven’t regretted it for a minute.

As technology changes, you may be able to find energy conservation measures in the garage. As a home energy professional, you may want to consider your clients’ transportation as a part of their overall energy consumption.

In cities across the country, walking, biking, and transit are becoming more viable as replacements for driving. Cities are investing in bicycle and pedestrian infrastructure to make active transportation choices safer and more convenient. Ride-hailing services like Uber and Lyft are growing exponentially as mobility on demand replaces prepurchased transportation. Considering these changes, your clients may not need to own two cars—and they can save a pile of money by unloading their second car.

These homes may be able to cut down their transportation costs. Once you start thinking about transportation energy savings, you'll find opportunities everywhere.

Imagine a home that has two refrigerators (I know I saw plenty of these during my years as an energy auditor). If one of them is empty and rarely used, it’s common sense to unplug the redundant unit and have it hauled away. Just like these spare refrigerators, second cars are slowly becoming redundant for many households. The trouble is that most people have never done the math to figure out how much money they could save if they sold their second car.

As a home energy auditor, you are in the perfect position to do an objective analysis that will reveal the true cost of the second car. With a few interview questions and the right formulas at your fingertips, you will have all the tools you need to estimate the savings your client could realize by selling that car. Plus, the math is about as easy as calculating the plug load on a refrigerator (no psychrometric charts required).

STEP 1: Go/No Go

You’ll want to find out two things before you do the math on transportation energy savings.

First, how many children does your client have? If the kids outnumber the adults, it may not be feasible to recommend selling the second car, because the children may go to different schools. If mom and dad have gotten into a pattern of chauffeuring their kids around, then it’s probably best to look elsewhere for energy savings.

Second, how many cars does your client have? If there’s only one car, it probably won’t make sense to proceed; the transition from one car to no car entails a substantial change in lifestyle. Only the densest urban areas can truly support this option.

STEP 2: Estimate the Fixed Costs for the Second Car

If it does make sense to consider selling that second car, first estimate the fixed costs of owning that car. Here are two methods to consider.

If your clients are willing to tell you how much they pay for a lease or auto loan, insurance, and registration, then you’re in luck. A brief analysis of these costs will yield the annual cost of ownership. Otherwise, you can estimate fixed costs from data available on the Center for Neighborhood Technology H+T Affordability Index. This web-based tool provides an annual auto ownership cost which it defines as “the cost of depreciation, finance charge, insurance, registration, and taxes (state fees) per auto.” I prefer this method, both because it respects the client’s privacy and because it accounts for depreciation.

Enter the home’s address; then use the drop-down menu to find Annual Auto Ownership Cost.

STEP 3: Estimate the Variable Costs for the Second Car

The variable costs are the costs of fuel and maintenance. Be careful here; getting this information can become a time drain. If your clients are fastidious about keeping receipts, you may be able to get the data directly from them.

In the more likely event that your clients don’t have these records, you will need to make an informed estimate based on the number of miles the car is driven per year. Your client may know this number offhand. If not, you can use the national average of vehicle mileage which is 11,244 for cars and 11,712 for light trucks.

To estimate the car’s fuel costs, convert the vehicle miles to gallons consumed using federal fuel economy data to obtain miles per gallon. Then convert the gallons into an annual cost, using the current fuel price for the area. The Energy Information Administration (EIA) has accurate regional data or, if you prefer, websites like GasBuddy have super local data. .

To estimate the car’s maintenance costs, look at the owner’s records. If you don’t have the owner’s records, AAA and Consumer Reports provide reliable estimates. The total variable costs equal the fuel costs plus the maintenance costs.

STEP 4: Assess the Client’s Alternatives

To determine whether your clients can dispose of their second car, you’ll need to know what destinations they travel to most often. Ask for the address of the workplace for each adult in the home, the children’s school or schools, and the grocery store.

A few minutes of light-duty mapping will show you if a second car is needed for these trips. Here are the benchmarks I suggest considering:

  • If the trip is 1 mile or less, it should be a good candidate for walking. You can also use the Walk Score website and your client’s home address to see what destinations are within a reasonable walking distance.
  • If it’s under 5 miles, a bike ride could replace the drive.
  • Longer trips will depend on the availability of useful transit. If a bus or train arrives once every 15 minutes or less, I would generally consider that useful for most situations. Walker (2011) discusses this subject in more detail.

You can use online mapping services to see if it's feasible to replace your client’s car trip with a walk, bike, or bus ride. When looking at these options, ask yourself if you would be willing to make these trips without your car—if you’re reluctant, chances are your client will be too.

Walking, biking, and transit directions are available from Bing, Google, and Open Street Map.

If one or more of these regular trips can be completely offset by one of your alternatives, then you’ve found a new energy conservation measure for your report! If not, skip ahead to Step 6 for some ideas on how to include other transportation energy suggestions in your report.

STEP 5: Do the Math

To determine how much money can be saved, I suggest that you start by calculating the potential energy and CO2 emission savings from the trips that can be made without a car. The combustion of 1 gallon of gasoline generates 8.8 kg of CO2.

Now for the fun part—calculating the cost savings. If you are recommending that your client dispose of a second car, add up the fixed cost savings (Step 2), the maintenance costs (Step 3) and the fuel savings (Step 4). The total represents the client’s gross savings. Finally, subtract the costs of transit passes and/or bicycles from the gross savings. The result is the cost savings realized by giving up the second car.

learn more

When making estimates about energy use or costs, it is always important to cite objective data sources. The links below will take you to reliable sources of information on transportation.

To estimate fixed costs for a second car, see Center for Neighborhood Technology H+T Affordability Index.

To determine regional fuel prices, go to Energy Information Administration's Gasoline and Diesel Fuel Update or Gas Buddy.

For federal fuel economy data, go to

To see which destinations are in walking distance of your client’s home, check out Walk Score.

To learn about local organizations that support walking, bicycling, or taking public transit, go to America Walks; Bike League; and American Public Transportation Association's Gateway to Public Transportation Links.

To estimate a car’s maintenance costs, see Consumer Reports and AAA Newroom.

Learn more about the Clean Cities Coalition.

Get DOE 2015 data on “Average Annual Vehicle Miles Traveled of Major Vehicle Categories,”

See EPA’s Greenhouse Gases Equivalencies Calculator: Calculations and References, 2017.

Walker, Jarett. How Frequent is Freedom? Blog post, 2011.

STEP 6: Encourage Change

Even though I started commuting by bike in 2012, it took me four years to realize that I didn’t need a second car! I cringe when I think about all the money I could have saved if I had sold it earlier—but the truth is that I wasn’t ready to make that sort of lifestyle change.

People’s transportation habits don’t change overnight. Consider making recommendations that are realistic for your clients while also encouraging changes that will benefit their personal finances and the environment. Luckily, there are lots of local organizations that support people who choose to walk, bike, and take transit. America Walks, the League of American Bicyclists, and the American Public Transport Association (APTA) can help you find the ones in your area. These organizations can help you to make a compelling case for walking, biking, and taking public transit, and can provide information about local transportation options.

Even if you conclude that it doesn’t make sense for a given client to switch to a one-car lifestyle, you can add money-saving transportation tips to your report. You can find dozens of fuel-saving ideas on the website. You may also want to see if there is a local Clean Cities Coalition in your area—these organizations have relevant information on local programs to reduce petroleum use. Don’t forget to check if your area has utility incentives and tax credits for electric vehicles. All these tips can be embedded directly in your report template, as they will apply to any budget-conscious client.

Recommendations for Your Clients

For decades, auditors have suggested recycling spare refrigerators. Second cars are simply the next major household energy-consuming asset to consider discarding. As cities continue to invest in bike paths and transit services, the utility value of personal vehicles drops, and that’s especially true for spare and underutilized cars.

Millions of families across the country are living with only one car. In my experience, these families are happy with their transportation options and are better off financially than their two-car counterparts. They’ve found ways to accomplish all the daily and occasional tasks expected of any family. As a home energy professional, you are in a unique position to make energy-related recommendations that help your clients live more efficiently.

  • 1
  • NEXT
  • LAST
Click here to view this article on a single page.
© Home Energy Magazine 2023, all rights reserved. For permission to reprint, please send an e-mail to
Home Energy Pros
Discuss this article with other home performance professionals at Home Energy Pros!.

Add a new article comment!

Enter your comments in the box below:

(Please note that all comments are subject to review prior to posting.)


While we will do our best to monitor all comments and blog posts for accuracy and relevancy, Home Energy is not responsible for content posted by our readers or third parties. Home Energy reserves the right to edit or remove comments or blog posts that do not meet our community guidelines.

Related Articles
SPONSORED CONTENT What is Home Performance? Learn about the largest association dedicated to home performance and weatherization contractors. Learn more! Watch Video