46 mpg in a Corolla!

I haven't posted here in a while because it seems like nobody is paying attention. I checked the counter today and noticed this blog is starting to show up on Google search in the top 10 of 37,000 for several searches and it is starting to get some good web traffic. Not bad!

I always chart my fuel economy in my car. For every tank of gas I record the amount of fuel used, cost of the fuel, approximate outdoor temperature, the miles driven, miles with the air conditioner on, highway miles, interstate miles, city miles, the weight I am carrying, and any other significant notes. I have a big Excel sheet with all of this information and I do many calculations with the data.

Last weekend I drove about 420 miles round trip to visit family and achieved my highest fuel economy ever: 46 mpg! The car is a Toyota Corolla S with manual transmission. It is rated with the old mpg rating system to have 32 city/41 highway mpg. The awesome thing about the high fuel economy is about 40% of the miles were on the interstate at higher speeds, and 70% of the miles required the air conditioner.

My lifetime average fuel economy with the car is about 36 mpg. Most of the miles I have driven between 3 and 5 mph over the speed limit. This past weekend was different, I never exceeded the speed limit on highways or the interstate.

The benefits of going slow was high fuel economy. The downside was mostly psychological. Driving 55 seemed like I was going very slow and I could be going faster. In reality, the difference was minimal. Driving just a few mph faster does very little for short trips, but for long trips a few mph can easily add up. I actually found the extra time required was negligible. It took me 3h 45min to make the drive one way at the posted speed. My previous trip was 5 mph over the speed limit for most of the time and it took me 3h 35min. I saved 10 minutes, but my fuel economy was about 8 mpg less.

In addition to driving slow, I do use mild hypermiling techniques that I have used regularly over the past several years. The main thing to do is just pay attention to driving, which you should be doing anyway. If you see a stop sign ahead, don't hold the gas pedal down until the last moment and then brake hard. You would be surprised how far your car can coast. For one highway stop sign on the route, I put my car in neutral 0.6 miles away from the sign and coasted in. When I hit my brakes as I neared the stop sign, my car was still doing 45 mph and had only dropped 10 mph from my previous speed. If there is a slight downhill grade, I can put the car in neutral even sooner. The extra time this added to my trip was very small, probably less than 5 seconds, but I was able to coast for 0.6 miles at probably 200 mpg or higher.

A similar technique can be used for stoplights. If one turns red, brake early to slow down, and then coast in. If you time it right, you will still be rolling and nearing the car in front of you as the light turns green. Slowing early will actually help you maintain a higher speed when the light turns green.

Two other things I do are slow acceleration and using my cruise control. These are simple things that will save you several mpg. I would not recommend drafting other vehicles as some others suggest. Drafting is unsafe and illegal.

The biggest time lost in the trip is not from the highway driving speed; city driving is the worst. As I travel through small towns, it is only 4% of the total trip miles but it takes 10% of the trip time. Doing the math, it only saves 12 minutes over the whole trip to drive 4 mph over the speed limit, which agrees with my observed results.

Changing interstate speeds back to 55 mph might not be such a bad idea. Even if people still go over the speed limit, the net effect will be lower overall speed and people using less fuel. For my 210 mile trip, the difference in time between current speed limits and if all roads were 55 mph is about 25 minutes. The benefits of increased safety and reduced foreign dependence on fuel are probably worth the extra time.