Crash Safety Vs Saving on Gas

Generally smaller, lighter vehicles can achieve better fuel economy than larger ones, all else being equal. The same basic physics means that the smaller vehicles will fare worse in crashes, once again all else being equal. That is not to say that small vehicles cannot be made to do well in crashes. Just that a larger vehicle with the same attention invested into crash safety will do better. Likewise, a larger vehicle can be more fuel efficient than a smaller vehicle if the smaller one has not invested the same level of engineering into fuel efficiency. This video explains some of the tradeoffs between crash safety and saving on gas.

Note that one concern is small vehicles colliding with large ones. That is a safety risk factor that will probably go away in the future, as sustained high and rising gas prices push automakers to elevate fuel economy to priority number one. That will likely result in all vehicles eventually being smaller, thus reducing the danger of a minicar colliding with a large SUV sized car. Even should this happen, there will remain the problem of smaller cars having smaller crumple zones, which leads to occupants experiencing higher accelerations in crashes. That is a basic limitation of physics and cannot be overcome.

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.

Truck Tailgating

Can you save gas by tailgating a semi? The idea is that the semi will force its way through the air, leaving a low pressure zone in its wake. If you can get your car into that low pressure zone, you will experience less air resistance. In turn that gives you better gas mileage. This principle applies when birds fly in V-shaped flocks. The leader opens a low pressure path in the air, making the journey easier for all of the following birds.

In the hypermiling lexicon this is known as drafting. The low pressure zone is not very large. The best area for drafting occurs within a distance of a couple of truck widths behind the truck. That is about 20 feet. The problem is that at highway speeds of 60 miles per hour, your car will cover those 20 feet in about one tenth of a second. This gives you essentially no time to react if the truck suddenly stops. Staying in this zone could give you up to a 20% reduction in gallons per hundred miles consumed. But tailgating is not only dangerous, it is illegal in many zones of the world. So the recommendation is to give tailgating a pass.

Biodiesel Burning Demonstration

It is actually pretty easy to make your own biodiesel at home. We put up a video by the Mythbusters in which they did nothing more than filter used French fry oil. The result was a sort of "biodiesel" which they then used to fuel a normal diesel car. This video shows that if you do want to make biodiesel at home you don't have to worry much about safety. Biodiesel in liquid form is very difficult to get burning. But as you can see in the ending sequence of the video, when it is atomized into tiny droplets with a high surface area to volume ratio it does burn. That atomization coupled with the high pressures in the cylinders of a diesel engine is why it works to power your diesel vehicle.



If anyone has the inclination to try making their own biodiesel, I want to encourage you. There was a time when people where much more do it yourself oriented. Today a big percentage of the population depends on buying premade stuff in department stores. If you know how to make things yourself it gives you a better understanding of how the world and our economy works. You know that products don't just appear on shelves because you have seen what it takes to make them. Also you are much more independent. If you can do it yourself you can also find a lot of chances to save too. Doing it yourself will also develop skills that you will keep forever, possibly offering you opportunities to sell your services in the future. Spending a few hours trying out biodiesel production at home will benefit you way more than sitting in front of Today's Reality TV Show for that same time.

Wheel Alignment is Not an Elective Service

Out of alignment wheels will decrease the gas mileage of your vehicle. They will also reduce the handling performance of the car, which makes it less safe to drive. And of course the lifetime of your tires will be shortened resulting in you spending more on replacement tires. When should you have the wheels aligned? Align your wheels after installing new tires or rotating the old ones. Have them aligned after replacing or having work done on the steering or suspension. Also go for an alignment after any collision repairs.

Keep your wheels in good alignment and you will save a percent or two on gas!

Road Rage: Just Say No!

Smooth driving that minimizes start and stop acceleration and braking and slower driving that minimizes air resistance are the keys to save on gas. Driving aggressively means you will wind up speeding up to the light and then slamming on the brakes, speeding and accelerating and braking constantly while weaving through traffic. It will reduce your gas mileage a lot, especially on the highway where you normally have a good chance of being able to maintain a steady, moderate speed. Aggressive driving is also less safe.

If you often find yourself pressured and stressed while driving think about how to calm down. Try leaving earlier to reduce "deadline pressure". Put soft relaxing music on. Avoid music that pumps you up. If being hungry makes you edgy, then always eat something before a long commute or trip. Have your morning coffee before getting behind the wheel. Don't let other drivers get to you. The competition is not against them but rather against the gas pump. Remember who the enemy really is. Slow down, calm down and you can be safer while saving on gas!

Do You Need a Bigger Car to be Safe?

One reason for choosing a big vehicle in spite of the gas savings hit is safety. Most people feel that a big vehicle will be overall safer to drive. Is that true? The Monash University Accident Research Centre tried to find out and the result was this report.

They looked at two measures of vehicle "bigness": the mass and a measure of the physical size such as volume or wheelbase length. The Monash study was one of those "study of studies" where they reviewed many other studies in the literature looking for common factors and data. The aim was to find how size and mass are related to occupant safety. There were problems getting definitive results due to the variability of the data. For example, some studies used interior cabin volume to measure size and others used wheelbase. But overall?

Overall they found that in multi-vehicle crashes (things like head on collisions, rear ending, sideswipes, anything with a least two cars involved) the bigger the vehicle mass, the safer the occupant. On the other hand, in single vehicle crashes (rollovers, hitting a tree, crash into a wall) the bigger the vehicle size the safer the occupant.

In multi-vehicle crashes it makes sense that bigger mass will help more. Physics says that the bigger car will always be least effected in a 2 way crash. It also makes sense that mass doesn't help much in single vehicle crashes. If you hit a wall or embankment, it doesn't matter how much mass you have in your car: the obstacle will always outgun you. On the other hand, if there is a lot of interior space, there is room for the vehicle to crumple, compress and slow down gradually without the driver's body being impacted by something.

How can we relate this to saving on gas? Well, careful design of interior cabin space can give us vehicle inner volumes that are as close as possible to the outer volume (no wasted space). Careful aerodynamics will let us make larger volume, light mass vehicles with little air drag. So in that respect, we can have safety and gas savings at the same time. But we need Detroit to play along and start designing vehicles accordingly.

With regard to mass, it is the direct enemy of fuel economy and they can't really be made to live together. But if all the vehicles on the road are lighter, being made of composites and modern light alloys, then what counts as a relatively "massive" vehicle in a two-way collision will also be lighter. We might see that over time, the "heavyweights" of the road become quite light compared to our heavyweights of today. That would open up the choice of driving a "heavy" car for safety and still saving on gas.