Guest blogger Greg Kushmerek continues his series of articles on bike commuting:
Last time I discussed how much something seemingly simple, parking, can have a strong effect on whether people cycle to work. Today I want to argue for the second seemingly simple thing that can make a big difference in whether someone cycles to work: having a convenient place to shower.
If you’re an American reading this, it might seem awfully obvious and almost a given. I say this as an American: people don’t like to smell your stink and you don’t like people smelling yours. On this basis alone, many people put biking as a non-starter. No place to clean up? No bike ride to work.
There are people who go through heroic motions. I read once about a guy who works out in San Francisco and cycle commutes. He’s got his place to park the bike, in a room in the basement of the building, and he also has adult-sized wet wipes to clean up from his ride. It makes for an interesting read, but I doubt that’s inspiring enough to spark a movement.
I’m fortunate: my employer has a gym on-site that includes a locker room with clean showers and towel service. I use this every time I come in. I keep a set of clothes at work that regularly go through a dry cleaning service (that I pay for) and I ride in with my shirt nicely rolled up — rolling helps prevent wrinkles. This makes riding in exceptionally easy from a logistics standpoint. I skip the shower at home and heck I save on hot water too. I consider this arrangement ideal.
So what could we do in designing our workplaces to make this available to more people? Many larger business have on-site gyms; if they provided safe bike parking then it’s easy enough to make the commute workable. It’s the medium and smaller places that are harder to manage.
One idea is to engineer change through the tax code. Businesses could receive tax credits if they provide a parking/shower package for cycle commuters. Sound outlandish? Businesses already receive tax breaks if they close down a building. That’s why some places stay empty for years but don’t get sold (I once worked at a place that redecorated a floor and then moved everyone out to claim the credit). A counterargument that nags at me is that the tax code is already so tortured that it’s become inefficient and costs society in a myriad of other ways.
What else? Well there’s the simple but blunt approach of making car commuting more expensive. The last time I checked, gas taxes didn’t even cover 60% of the cost of maintaining roads meaning that non-drivers are continuously subsidizing the roads that they don’t use. Here again is where I have some sympathy with the Libertarian point of view: if people find the service is worthwhile, then make people pay for it. I don’t want to privatize the Fire Department, but I do think the subsidy to car drivers is ridiculous and they should pay more for the roads they use as well as for the times they use them (look up “congestion charging” for more on this idea).
Whether through congestion charging (design) or market forces (demand as in $4 gas when the world economy was humming), a smart business will see the advantages of putting in more parking and showers to attract tenants. After all, once companies start to hire again, how better to burnish Green credentials than to promote their friendliness to cycle commuters?
Please welcome the newest Design Impact guest blogger: Sterling Anderson. Sterling is a Ph.D. student at MIT working in the Robotic Mobility Group. In today’s article, Sterling writes about his work in the next generation of vehicle stability and hazard avoidance control, and how it relates to vehicle sustainability.
Today I’d like to briefly discuss exciting new developments in a field not commonly associated with or considered a critical component of vehicle sustainability. That field is vehicle safety. The connection I’d like to draw between safety and sustainability goes as follows: no matter what its energy source (gas, hybrid, electric, etc), a vehicle may be made more efficient by removing or otherwise lightening its structural elements. Many of these elements, however, such as secure seat belt harnesses, large airbag systems, sturdy roll cages, and large crumple zones, cannot be removed without increasing the risk of injury to vehicle occupants in the event of a collision. This limits the degree to which vehicles can be made smaller (which reduces drag), and lighter (less mass) without forfeiting the structural protection provided by larger and more massive vehicles.
Enter driver assistance systems. In recent years, the historical focus on passenger safety in human-controlled motor vehicles has shifted from collision mitigation systems such as seat belts, airbags, roll cages, and crumple zones to collision avoidance systems, which include anti-lock brakes, yaw stability control, roll stability control, and traction control. Whereas collision mitigation systems seek to reduce the effects of collisions on passengers, active collision avoidance systems seek to prepare for and avoid accidents altogether. This accident avoidance reduces – and may one day eliminate – the additional mass and design constraints required by passive safety systems.
But while existing collision avoidance systems are effective at reducing accident frequency, they are still limited in one respect: their avoidance methods are fundamentally “reactive” in nature. In the majority of these systems, controller intervention is based solely on current vehicle conditions, and thus cannot anticipate and prepare for future threats. For example, an anti-lock brake system seeks to help the driver avoid accidents by more intelligently applying his intended braking command – it does not preview the road ahead and decide to apply the brakes of its own accord. Ditto with stability and traction controllers; neither preemptively seeks to avoid hazards – each simply responds to the driver’s command. Thus, a drowsy, distracted, or otherwise inattentive driver receives very little benefit from such a system as it does not engage until he begins his own evasive maneuver.
Recent developments in onboard sensing (cameras, radar, laser-based sensing, vehicle-to-vehicle communication, etc.) and drive-by-wire technology have facilitated the development of collision avoidance systems that use information about the vehicle’s surroundings, along with predictive computer models to determine the best course of action to avoid an accident. If needed, such systems intervene and share steering and/or braking control with the driver. These “predictive” systems generally attempt to honor driver intentions, opposing them only when doing otherwise would lead to a collision or loss of control. By constantly monitoring a vehicle’s surroundings and predicting a safe path through them, they may warn the driver and take control of the vehicle steering and/or braking to avoid accidents before it is too late. Much like a copilot or driving instructor, this controller intervention should strike a necessary balance between the level and frequency of intervention: not altering the driver’s steering and braking inputs “too much”, “too soon”, or “too often” while still guaranteeing that the vehicle avoid hazards independent of that driver input.
In my work with MIT’s Robotic Mobility Group, we are currently developing a predictive active safety system that predicts the “best-case” trajectory through the environment, assesses the threat this trajectory poses, and intervenes as necessary to avoid accidents. We’ve tested this system in both simulation and experiment with excellent results. As the patent is still pending, I’ll defer details until my next post. Until then, you can see a demonstration of its performance in a few simulation videos posted here. In the mean time, and before I’ve biased your creativity with our solution, please brainstorm your own possible solutions. We have the technology to identify hazardous conditions and help the driver avoid collisions. What would you think of driving a car with a system like this? How do we know when intervention is “too much” or “too soon”? Feel free to discuss these ideas with others via the comment section below.
My earlier post, What Cycling Can Teach us About Better Driving, addressed how spending some time biking can help us become safer and more fuel-efficient drivers. This article prompted some insightful feedback from readers via blog comments, email, and LinkedIn. Here is a summary of what I heard from you:
Interaction: Cyclists learn to establish communication with motorists around them to ensure drivers are aware of their intentions, and vice versa. Drivers with experience cycling tend to be more vigilant with things like using turn signals, since they appreciate the importance of informing other road users what they plan to do. A motorist failing to use a turn signal can in some cases be a severe hazard to cyclists. One reader suggests always driving with lights on to help cyclists who use mirrors, particularly in foggy conditions. Another reader observed that establishing eye contact is ‘an important mode of communication’ for both cyclists and motorists.
Awareness: Cyclists develop the habit of being very aware of what’s going on around them. The habit of checking to see who is around you and what they are doing carries over to driving, as well as being extra alert for cyclists. Experience cycling gives drivers some insight into where to look for cyclists and what to expect from them.
Interpretation: It’s possible to discern much of what a driver is planning to do by paying attention to ‘body’ language, whether the actual behavior or facial expressions of the driver, or vehicle positioning, movement, or even what direction a car’s wheels are pointing. Cyclists develop these skills by necessity; drivers with enhanced anticipation and interpretation skills can drive more defensively and safely.
Appreciation: Exprience cycling helps motorists understand just how much space cyclists need while being passed, and the wide variation in speeds cyclists can travel at. It’s important for motorists not to assume all cyclists are travelling slowly; underestimating speed can lead to trouble. In addition, minor road hazards that might not mean anything to a motorist (like some road grates) are significant obstacles for cyclists; if driver’s can recognize this they can anticipate cyclist actions better. One reader ‘would like to see laws requiring cycling skills as part of driver’s licensure’ to help drivers gain a deeper appreciation for the dangers and challenges faced by cyclists. Another reader pointed out that drivers in the Netherlands are ‘far more considerate of cyclists’ because so many drivers also cycle.
In the second installment of this series on ultra-efficient vehicle design, I cover briefly the aerodynamic design of solar cars and the related opportunity for significant improvement of production passenger cars.
Air resistance is very important consideration for solar cars, or any vehicle that travels at high speeds, since the power to overcome air drag increases cubically with speed. In other words, if you double your speed, the power required to overcome air resistance increases by a factor of EIGHT.
I’m going to jump right into an equation that will help illustrate some of the main concepts in this article. The force of air pushing back on a moving car, the aerodynamic drag force (), can be approximated by this formula:
where is the density of air, is the drag coefficient, is the car’s frontal area, and is the car’s velocity (speed). This equation is a simple engineering model (see my ongoing series of articles on modeling) that helps us understand how changing vehicle design and operating conditions affects aerodynamic drag force. Looking at this equation, we can see that drag force increases quadratically with speed (that is, doubling your speed increases drag force by a factor of four), and increases proportionately with frontal area and drag coefficient. Based on this equation, what can we do to reduce drag force? Obviously the most effective thing to do is reduce speed. This is why freeway speed limits were reduced to 55 mph years ago to save fuel. Let’s assume for now that the speed we want to drive our car at is fixed. What else can we do to reduce drag force? We can’t do much about reducing air density (), but we can control frontal area () and drag coefficient (). In my last post on solar car design, I explained that solar cars must make do with very limited amounts of power (less than what a hairdrier consumes). Reducing frontal area and the drag coefficient can bring solar car designers one step closer to building a car that can travel at highway speeds with only the power from the sun.
In the past, solar car racing rules allowed drivers to pretty much lie down in the car, making it possible to design cars with a very small frontal area. This really helps reduce air resistance (cyclists understand very well the importance of keeping a small profile), but makes getting in and out of the car fairly challenging. Current solar racing rules now require a more upright driver position, resulting cars that are a little closer to what commuters might consider driving. Some teams have even built two-person solar cars. While somewhat more practical, solar cars with upright seating have increased frontal area and increased air resistance.
So what about the drag coefficient? Vehicle designers can adjust the shape of the car so that air flows around it smoothly, requiring less force to push the car through the air. Solar cars are perhaps the most streamlined road going vehicles. They have smooth surfaces that taper toward the rear, ensuring that air flows over them in a smooth, laminar way. The blunt rear edge of most cars leads to a lot more air resistance, as opposed to the trailing edge of a solar car or the the Aptera 2e. Have a look at these simulation results that show how air flows smoothly over the University of Waterloo solar car without much disturbance:
The streamlined shape slices through the air without generating a turbulent wake at its tapered rear edge, in contrast to many production vehicle with blunt rear ends. Solar cars have acheived drag coefficients as low as 0.10, while the Prius sports a much larger and less efficient drag coefficient of 0.26 (which is actually the lowest of any production car). Referring to our drag equation above, that means if a Prius and a solar car had the same frontal area, the Prius would take 2.6 times as much force to overcome air resistance as the solar car at a given speed. Most production cars have noticeably higher drag coefficients; a Civic’s is 0.36, and a Hummer H2’s is 0.57. The image below illustrates how other vehicle shapes can lead to turbulent wakes, which increases a car’s drag coefficient:
While reducing drag coefficient is a paramount consideration in solar car design, it is not the only consideration. Goro Tamai, a past MIT solar car team member, discusses in his book, The Leading Edge, that aerodynamic design must be considered as a component as the overall vehicle system.
The “best” body shape for solar cars, HPVs, or Electrathoners is not the body of absolute lowest drag. The vehicle system, including the driver, chassis, and energy/drive system must work in concert to produce the maximum output.
In addition to minimizing drag, designers must ensure vehicle stability and safety, and that aerodynamic design works in concert with powertrain and power production systems to acheive the best overall vehicle performance. In the case of a solar racer, the measure of ‘best performance’ is how fast the car can safely travel a set route, powered only by the sun. I’ll explore the importance of systems engineering in vehicle design in a later article in this series.
So how do these ideas transfer to production vehicle design? First of all, the low drag coefficient of solar cars compared to production cars is astounding. Clearly low drag is not a top priority in production vehicles; there is tremendous room for improvement. Solar cars illustrate what is possible, and give some insights into how to do it (smaller frontal area, tapered rear edge, smooth undersides, and wheels covered by fairings, for example). Spencer Quong, a senior vehicle analyst with the Union of Concerned Scientists, has explained that solar car development “opens the industry’s eyes to how to build a more efficient vehicle.”
A recent article from allcarselectric.com claims that the new Honda Insight looks so much like the Prius because when you optimize a vehicle for aerodynamics, you converge on something that looks like the Prius. Considering our discussion above, the shape of the Prius clearly is not aerodynamically optimal. It’s good, but it’s possible to do much better. I suspect that marketing and visual cues are much bigger factors here than truly slippery shapes. Prius styling is becoming a symbol of ‘green’, its shape now spark thoughts of energy efficiency. If the objective was to minimize drag, I contend that designers would arrive at a vehicle shape closer to the Aptera 2e.
An auto manufacturer obviously needs to build cars that people want to buy. They need to perform well and look good. We have the ability to improve performance and energy efficiency of production cars by moving toward more streamlined shapes, but would many people buy these cars? What do you think could be done to shift public perception and preference such that genuinely low-drag vehicles could become marketable? This is an important question; developing demand for vehicles with dramatically lower drag would have considerable impact on energy consumption.
A team of students from Ohio State University took first place at the 2009 EcoCAR Challenge today. Here is an excerpt from the press release:
The Ohio State University took first place out of 17 universities in the U.S. and Canada that competed in the first major milestone of this three-year competition which is sponsored by the U.S. Department of Energy, General Motors, and many others including the Government of Canada. The competition challenges university engineering students across North America to re-engineer a 2009 Saturn VUE to improve fuel efficiency and reduce emissions while retaining the vehicle’s performance and consumer appeal. …
The winning team’s EREV provides a practical solution that will increase energy efficiency and reduce environmental impacts. The Ohio State’s design was powered by a 1.8 litre engine and fueled by E85 ethanol. The next-generation design predicts a 300 per cent increase in fuel economy over the production 4 cylinder vehicle.
Please welcome back Greg Kushmerek for another installment in his series on bicycle commuting. He contributes every second Wednesday, and you can read his previous posts here and here.
I’ve spent time so far discussing general issues that affect anyone considering using a bike for transportation. Today I want to think about issues of infrastructure development that support cycle commuting specifically.
Why cycle commuting? Most Americans commute by car, and increasingly those car trips are by solo drivers. Anyone familiar with rush hour traffic knows all of that stop and go is bad for gas mileage. In other words, we have plenty of people spending time creeping through traffic on a daily basis burning hydrocarbons when they could be on a bike instead. Put more commuters on a bike, and I think you’ll have a greater number of healthy (and less-stressed) people breathing cleaner air.
What helps support cycle commuters? If your bike commute is short, your interests include parking. When I lived and worked in The Netherlands, my company had two large bike racks right out front with overhead cover. Think about these attributes: these commuter bicycles were not relegated to the back corner behind a dumpster where vandals and thieves can prey in privacy during work hours. Access from the rack and the front door was just as quick as for any car in the lot, and a rainstorm, a daily guarantee, would not mean a wet seat awaited you for the ride home.
Don’t underestimate the need for a place to park. A friend of mine gave up his daily 3-mile cycle commute because the management company of his Kendall Square firm wouldn’t let him park his bike inside. It didn’t matter that there was space in his office and his company was OK with it; the lease said no and the bike had to go. There wasn’t any nice bike rack out front either. If he wanted to bike in, he faced leaving a theft magnet locked to a parking meter.
Just one mile away, anyone visiting the Brigham and Women’s hospital in Boston’s Longwood medical center can park their bike for free at one of the many racks in the parking garage. Your bike is by the attendent collecting cash from car drivers exiting the garage and right next to the main door in to the facility. These racks are heavily used during the day: free parking, a protected space, easy access to the door. Many companies could provide the same at a minimum of cost. Convert a few spaces in a parking garage into bike racks. Put those racks in a decently trafficked area. The same happened when Boston Healthcare for the Homeless built a new facility at the Boston Medical Center. The parking structure was created with cyclists in mind. Bike in there, and you have a protected bike spot in a highly visible area. Many of the staff converted to cycle commuters so they wouldn’t have to park in overflow a half mile away.
Is crime a concern? Some companies have bike lockers where four people share the space, limiting the list of suspects if something goes awry. This is a feature people are even willing to pay for if the traffic density is high enough. I’ve heard of waiting lists to get into these kinds of setups.
My favorite idea along these lines is one I first saw pop up in Chicago: the McDonald’s Cycle Center, a secure bike parking center that provides indoor storage and a locker/shower facility for yourself. I’ve been inside: it’s clean and well-located. Bike in, change, and either walk to work in your nearby downtown office or hop the L and go. The center even offers an on-site bike mechanic — and any cycle commuter worth his or her salt knows where the bike shops are on the way into work and when they open. These types of places are perfect for existing high-density cities.
Do you think your city has enough density to support a facility like the McDonald’s Cycle Center? Has your employer ever considered converting car spaces to bike spaces in a garage? Have you asked?
Recently I wrote about my visit to the MIT solar car team; this post is the first in a follow-up series that addresses the phenomenal efficiency of solar cars, and how innovative vehicle design techniques used in solar car development might influence design of future production cars.
Solar cars are amazingly efficient. The have to be if they are to drive continuously, powered only by the sun. If they have no other power source, solar cars must operate on only they power they can collect from their solar arrays (which is pretty limited). Let’s look at some rough numbers. When conditions are good, a horizontal square meter of ground receives about 1000 Watts of power from the sun. Photovoltaic cells are semiconductors that harness the sun’s radiation and convert it directly to electricity. The cells used on the MIT solar car are 21% efficient. That means 21% of the sun’s energy hitting the solar array is converted to electricity. Suppose we have a car with a solar array that has six square meters of area pointed directly at the sun. This array then has 6 m2 x 1000 W/m2 = 6000 Watts of solar radiation hitting it, and produces 0.21 x 6000 W = 1260 Watts of electrical power available to power the car. This is not much at all (about as much power as a hairdryer uses). 1260 Watts is best-case scenario as well; clouds or low sun angles early or late in the day reduce power production significantly. For comparison, a typical 150 horsepower car engine produces almost 112,000 Watts, or almost ninety times the peak power of our 6 m2 solar array. A solar car needs to squeeze every last bit of efficiency it can from all its systems to make it possible to run a car on such little power.
So how solar car designers develop a car that drives at freeway speeds with less than one horsepower? We will look at five main factors in vehicle energy consumption: air resistance, tire rolling resistance, vehicle mass, powertrain efficiency, and system design. I’ll explore the differences between solar cars and conventional cars along these five dimensions in a series of upcoming posts. While it’s impractical to start building production passenger cars the way solar cars are built, we can incorporate many elements of solar car design in future vehicle designs.
Have any of you seen a solar car? On the road? Or even better, have you actually driven one?
Now that bike month is drawing to a close, it’s a great time to reflect on a few things that can be learned by riding our bikes more. In particular, what can cycling teach us about driving? It helps us learn two main things: how to drive more safely, and how to drive more efficiently. Cyclists must be the ultimate defensive drivers, and more frequent cycling can help us develop safer defensive driving habits. With respect to energy efficiency, the cyclist is his/her own power source, and so he or she is very aware of the energy requirements for different activities while riding. Recently I read through again the 100 tips for more efficient driving suggested by Ecomodder, and realized that many of these tips are learned naturally by riding a bike. Most cyclists tend to adjust their riding style to reduce their energy output; we get instant feedback on energy requirements, and have good motivation to minimize them. Here are some examples of things cyclists learn that transfer to efficient and safe driving of autos:
Momentum: It takes a lot of work to build up speed on a bike. Cyclists really appreciate their momentum. This gives you a sense of what might happen if you hit something with all that momentum, but it is also motivation to maintain your momentum. When you brake, all that kinetic energy is dissipated as heat from your brake pads, and then you have to redo all that hard work to get your momentum back up. When driving, you save energy by avoiding routes that require frequent starts and stops. This helps maintain your momentum. Alternate traffic control devices could also help. Replacing stop signs and traffic lights with yield (give way) signs and roundabouts helps drivers keep up their momentum, not to mention cutting down on wasteful idling and time lost sitting in traffic.
Gravitational Potential Energy: Pedaling up a hill can take a lot of work. It’s hard for a cyclist to let all that work go to waste by not maintaining speed developed by going back down the hill.
Anticipation: This is a key skill. We can tie together items 1 and 2 with the idea of anticipation. For example, if you are at the top of a hill, and there is a stoplight at the bottom, but you anticipate that it will turn red, then stop and wait at the top until the light turns (or time it so that you get to the light when it turns green) so that you can maintain your speed through the intersection. A cyclist also learns to keenly anticipate intentions of drivers as part of being a defensive rider. Cyclists learn how to look ahead, think ahead, and plan ahead. Drivers could benefit substantially from improved anticipation skill.
Small Profile: When you are riding fast or in windy conditions, the effect of air drag is very clear. Cyclists learn that crouching down and making yourself small cuts down significantly on drag force. Similarly, cars with a small profile, and fewer extra protrusions (like roof racks), have less drag. This can be especially important with cars since they generally travel much faster than cyclists. The power required to overcome drag force increases cubically with speed, that is, if you double your speed, it requires EIGHT times as much power to overcome drag force from air resistance.
Drafting: This is actually not so advisable for driving, but cyclists who have ridden in a pack understand the benefit of drafting. Basically, cyclists take turns in the lead position, and cyclists who follow behind benefit from lower air resistance. Average speed is noticeably higher when riding in a pack and drafting.
Good Tire Pressure: Anyone who has ridden with low tire pressure can attest that their bike is very sluggish compared to when their tires are fully inflated. It’s amazing to feel what a difference airing up your bike tires can make. It does make a difference with your car, but you don’t feel it the same as you do with a bike.
Well-tuned Drivetrain: A well-lubed chain and tuned shifters makes a bike a joy to ride. Otherwise it can be a struggle. Keeping your car in tune is also essential to efficient driving. Be sure to find out what the engineers who made your car recommend for maintenance, and stick to it. Back when I was an auto technician (clear back when there were a lot of carbureted cars still on the road), I found it very satisfying to take a poorly running car, tune it up, and see immediate big differences in how it drove, as well as big reductions in exhaust emissions.
Smooth Roads: Cyclists can sail over fresh, smooth roads so much more easily than rough terrain. Plowing through sand, mud, or snow takes a lot of extra effort. The same holds true for cars. Driving on dirt roads or through the snow burns more energy than driving on smooth asphalt.
Interaction and Courtesy: Cyclists are out in the open. Everyone can see our body language. We don’t have anything to hide behind, so it’s important to keep emotions in check. To be defensive riders, cyclists learn to interact and communicate with drivers as much as possible, to be sure each knows the other’s intention. Travelling in an interactive and courteous way can be much more pleasant (and safe) than driving in isolated bubbles.
The list above is far from comprehensive. Can you share with us things you have learned while cycling that helped you become a better driver?
By now most of you have probably heard about the Tesla Roadster, Fisker Karma, and other high performance electric cars that demonstrate we can make spectacular gains in energy efficiency AND enjoy amazing performance by designing cars in a new way. Improving efficiency and performance simultaneously is an impressive feat. These are competing objectives, that is, improving one objective normally involves degrading the other. We can design a car that is either high performance or highly efficient, but not both. We can visualize this kind of design tradeoff using a tradeoff curve usually called a Pareto curve or efficient frontier. The drawing below is a conceptual illustration of a Pareto curve in automotive design, showing the tradeoff between performance and efficiency.
We would like to maximize both performance (one aspect of performance is acceleration) and energy/fuel efficiency. Ideally we would like a design that is in the upper right corner of the plot above. Unfortunately, when a design tradeoff exists, this is not physically possible. We can’t focus on both performance and efficiency because they are competing objectives. If we focus on performance in vehicle design, we might end up with something like a Porsche 911 Turbo, which has a blistering fast 0-60 mph time as low as 3.2 seconds. Unfortunately this car doesn’t get great fuel economy. If we want to improve fuel economy we will need to sacrifice performance, that is, we will need to trade some performance for fuel efficiency (perhaps by reducing engine size, using smaller tires, reducing mass, etc.). If we focus on just fuel efficiency we might end up with something like a Geo Metro. The Pareto curve connecting these two points on the plot above represents what designs in between the Porsche and Geo are physically realizable. It’s not possible to create a vehicle to the upper right of the curve. Something on the interior of the curve is not Pareto optimal, meaning that it’s possible to improve both objectives simultaneously. Designs on the interior of this curve are to be avoided. Advanced design techniques, such as simulation and design optimization, can help engineers ensure that their designs are on the Pareto curve. It is up to the engineers and market analysts to determine where on the curve their product should be.
What if we changes the rules of vehicle design? What if instead of assuming powertrains had to include a conventional gasoline engine linked to a manual or automatic transmission, we allowed battery electric powertrains? The previously impenetrable Pareto curve shifts to the upper right if we can escape the inefficiencies of gasoline engines. New technology, and new ways of designing things, can push the Pareto curve to a new and better location, as shown in the diagram below. We can improve both performance and efficiency by introducing new technology. This is what’s going on with the Tesla and Fisker. The Aptera 2e places more emphasis on energy efficiency than performance, and solar cars are the ultimate in energy efficiency. The Prius uses a power split hybrid electric powertrain. It’s an improvement in efficiency over conventional powertrains, but it can’t compare in efficiency to pure electrics like the Aptera (that’s why it is a design on the interior of the Pareto curve). In fact, although my crude diagram doesn’t really depict this, the powerful Tesla gets better energy efficiency than the Prius.
The Tesla might be a fast EV, but have a look at the X1 Wrightspeed. It’s wicked fast. See where it’s positioned on the Pareto curve? The X1 is an Ariel Atom retrofitted with an all-electric powertrain created by AC Propulsion, makers of the eBox. Here is the X1 smoking both a Ferrari and a Porsche:
Now that’s what pushing out the Pareto curve looks like! Here is another race between the X1 and a Lamborghini, and then with a NASCAR racer:
The above analysis is admittedly simplified. The diagrams are conceptual and do not represent actual performance and efficiency numbers (if they did the solar car point would be way off to the right of your computer screen). In addition, there are many other competing objectives that need to be considered in vehicle design, such as range, safety, durability, utility, cost, and total lifecycle environmental impact. Nevertheless, Pareto curves are a helpful tool for visualizing and understanding design tradeoffs.
What emerging technologies do you think will expand the current Pareto curve for vehicle design (or other products)? Can you think of some additional tradeoffs important to vehicle design that I haven’t listed here? If we want to look at three, four, or more competing objectives, how do you think we can visualize the tradeoff relationships between them?
), can be approximated by 
is the density of air, 
is the drag coefficient, 
is the car’s frontal area, and 
is the car’s velocity (speed). This equation is a simple engineering model (see my 
