Does Avoiding Left Turns Save Gas?

Taking a left turn often means waiting for a light or an opening in oncoming traffic. Time spent with the engine idling means fuel spent. On the other hand, right turns can be made without waiting. A left turn can be replaced by three right turns. Of course, three right turns make the total distance travelled greater. So the question arises: can you save on gas overall by only making right turns? The distance will be greater, but the time spent idling could be lower.

The answer will depend on the vehicle, traffic patterns, type of route and many other things. In particular cases the difference can be measured. The videos below show the Mythbusters television program's experiments on the issue.

Know Your Way to Save on Gas

Many drivers burn fuel needlessly becoming lost. Very often, we head towards our destinations without being clear on exactly how to get there. The result is time and fuel spent driving in loops looking for the right route. This lost time and gas can be saved by examining a map or using a GPS mapping device so you can plan out the directions before starting out.

ecoRoute Route Planning Aide

Choice of route can save on gas. Shorter paths are generally better than longer paths, but there are complicating factors. For example, a shorter path which has you stuck in stop and go traffic could burn more gas than a somewhat longer route on an open road. Remember that slowing down or stopping only to speed back up again wastes all the kinetic energy which you had to pay for with fuel. There are various route planning programs which can help you deal with these factors. The video introduces one.

Online Route Planner

The TomTom website is an interface to some pretty sophisticated route planning software. They maintain an up to date map of road networks in several countries and are able to combine that with real time traffic data to show you what they consider the best route between two points. They use the traffic data to find the shortest time route based on the predicted travel speed. The video shows off the website.

Two potential pitfalls with the route planner are 1) it is based on minimum time and 2) it offers only one choice of route. Many or possibly most drivers are indeed looking for the minimum time path between the start and the destination. However, minimum time might not be minimum distance or minimum fuel consumption. For example, a high speed low traffic route which goes over several large hills will get you to the destination quickly, but those hills could really harm fuel efficiency. A different route which avoids the hills could take a little more time but save on gas.

Providing only one route to the driver is also quite limiting. There could easily be several routes to a destination which differ only minutes in time. The website seems to always pick the single route it considers absolutely shortest. Imagine a situation where there are half a dozen routes between two places, with predicted travel times ranging from 2 hours 5 minutes to 2 hours 20 minutes. A difference of 15 minutes on top of a 2 hour drive is not very much. However, there could be other factors to choose from between the routes which are very different. For example, some routes could include toll roads and others not. Some routes might go through dangerous neighborhoods. Some routes might include a lot of hills. Some might be more scenic than others. Some might have more potholes or rough pavement.

All of these factors are things the website does not know about. Different people would weight these factors differently anyway. For example, some people would be happy to drive an extra 5 minutes to avoid paying a toll and others would not. Given these other factors, I believe it would be better to have a route planning software that offered a selection of all routes with approximately the least time. Then each driver could choose among these routes to find their best trade off between minutes and everything else.

Trip Gas Price

The Fuel Cost Calculator is a website which will calculate the amount of gas needed to travel between any two cities in the US based on the year, make and model of the vehicle you choose. The cost of the gas is also calculated based on current prices. You can see the effect of vehicle choice here quite clearly.

Let us consider a there and back road trip from Miami to Seattle. The route trip distance is 6658 miles. Doing it in a 2007 Ford F150 pickup will use 370 gallons of gas and set you back $1,007. On the other hand, taking a 2007 Toyota Prius will go through 130.5 gallons and cost you $356. This website could be a handy tool to see how much you will have to budget for when planning your road trips.

A Pantry Can Save on Gas

Remember those not so far gone years when everybody kept a well stocked pantry? Or a shelf or two of preserves in the basement? Keeping a stock of food can help you save on gas by reducing the miles you drive. If you find yourself going to the store every day to pick up a couple of things you will rack up the odometer pretty fast, burning gas while you do it. Consider instead going shopping less frequently and buying more. Make one big grocery run every week, or even every couple of weeks.

Maintaining a store of food and other consumibles in your house has gone out of fashion in today's just in time world. But it brings more benefits than just reducing gas usage. You will save on time too. All of those "convenience" trips add up to more time than one big monthly run. And you will always have an emergency supply. For those unpredictable times when something happens, like a big storm or the power system goes down you will be ready.

Bridges and Bottlenecks

Bridges are something that most drivers take for granted. They enable some really impressive shortcuts. Yet the nation's bridge population is old and in need of maintenance. Even now important bridges are closed. The Bay Bridge in Oakland, a 73 year old piece of critical infrastructure is closed to traffic. The Lake Champlain Bridge is also shut.

Given the very high levels of federal and state government debt and the poor condition of the country's bridges I think we will be seeing more and more closures in the years ahead. A cash strapped state or local government might find it does not have the budget to make repairs. Bridges could be shut for extended periods.

Try to become aware of the bridges along your commonly driven routes. They don't have to be bay crossing monsters. Even a small bridge over a dry ravine can be critical in a route. Having an awareness of the infrastructure that lets you drive carefree where you want will help you cope if that infrastructure fails. Also if you find yourself planning a move, you might want to include a study of bridge layout when evaluating your options. Living in a city or region that is heavily dependent on bridges could prove to be a mobility limiting headache over the next decade or so.

Bad Bridge Maps

When you are doing your route planning you may find yourself with the choice to cross a bridge or not. Perhaps you have heard about the thousands of deficient bridges scattered across the nation and wondered whether the bridge you are choosing to cross or avoid is one of them. Well, the Bureau of Transportation Statistics has a map showing the locations of the structurally deficient bridges on the National Highway System. You select the state you are interested in. Then you can choose to see a map for that entire state or for one of the individual congressional districts it contains. Each deficient bridge is marked with a green dot. For example, the map for Idaho is shown below. Also available below the image is a table of data giving the bridge's label and structure id number as well as the highway it is on and a rough description of where it is along that highway.


Being paranoid is never a good idea, and going far out of your way to avoid a bad bridge could cost you a lot of extra gas. But if you are the cautious type and have an easily avoided bad bridge on your commute (or otherwise well beaten path) you could choose to go another route.

Route Planning to Minimize Gas Use

When you have a choice of routes for example for your commute, sometimes choosing the longer one can save you gas overall. A route that lets you drive smoothly at a lower speed without accelerating and stopping will give you better gas mileage. But if the smooth route is a lot longer, it might actually cost you more gas overall, even though you get better MPG. Remember that your real goal is to minimize fuel use, not maximize fuel economy. Of course these two goals are normally the same thing. If you are traveling a fixed distance for example because you don't have a choice of routes then better fuel economy will give you less gas use overall. But when the route or distance itself becomes a variable, then sometimes the shorter route that gives you lower fuel economy could be better. For example, if you have an amphicar, you won't get very good mileage, but shortcutting across a lake could save you so much distance you use less gas overall. Or more realistically, it could be that you can choose to take your commute route over a steep hill. Going over that hill will lower your mileage drastically, but if the distance you save is great enough you could use less gas overall on the commute.

Think about the routes you can take to get where you want to go. Try to pick the one that balances opportunities for smooth, slow travel (use less gas per mile) and cuts down on the total distance. You want to choose the one that uses the least gas along the trip.

That Hill Kills (Your Fuel Economy)

Going up hills costs a lot more fuel than you may think. After all, your car is doing all the work so the driver doesn't notice. The chart shows the power used by a 1995 Ford Taurus engine as it moves the vehicle along at a steady cruise speed on the level, as it climbs a 6% grade at constant speed, and as it accelerates on the level. You can see that depending on speed, going up the grade costs from triple to double the power. Power translates to fuel. To give an idea, a power output of 20 kW (the units shown on the chart) costs you about 2.1 gallons per hundred miles (GPHM). Remember that the chart shows the power output of the engine. After taking into account powertrain losses (in the transmission, differential, etc) it will cost you more than 2.1 GPHM.

The lesson is to avoid hills like the plague. If you can take a slightly longer route that detours around a hill instead of climbing over it and coming down the far side, do it. Figuring out these route adjustments is easy with an instrument like the scangauge. If you have to climb a hill, see if you can rearrange your trip so you do it after the engine is warm. Cold engines are less efficient. The last thing you want is to take a hill with an efficiency penalty. If you have to carry cargo during a series of trips, think about if it is possible to drop it off before taking a hill. If you are planning to move to a new house, think about picking a location where you can commute to work on the level. If you work in a valley, don't live up on the ridge. Climbing it every day could inflate your gas bill!

Think about the Price, not the Brand

Try not to think much about the brand when you fill up your gas tank. Look for the station offering the best value for your money. Remember that gas is a fungible commodity, which is econospeak meaning that gas is a widespread and interchangeable product. It really does not matter which brand you buy or what the logo on the pumping station sign is. All gasoline sold in the US must meet the basic standards set by the government. It is true that each brand might put in their own cocktail of chemical additives, but these additives are also government controlled. In fact, many gas stations will buy their gas from the same refinery no matter what the brand. Smaller cities might have only one refinery close by.

So to save on gas, think about value for your money and not brand loyalty. Remember that the brands are sure not loyal to you, so why should you be loyal to them? While you are thinking about value for your money, remember to include distance to the station. A station with cheap gas that is a distance away might cost you more after taking into account the gas you burn going there and back.

Right Turn Theory

How many times have you been waiting in busy city traffic to make a left turn? Sometimes you have to wait for 2 or even 3 cycles of the light before it is your turn. Ever thought that maybe you could get where you are going faster if you took a different route, one that only made right turns? City road layouts are often based on square grids, and when you stop to look at it, on square grids you can go between any two points making either right or left turns.

Even if the all rights route is a little longer, you might actually get there in less time. And if you are not sitting idling the engine in line at the left turn light, you will also save on gas.