Energy-efficient driving

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Terms for driving techniques to maximize fuel efficiency include hypermiling.[1]




Underinflated tires wear out faster and lose energy to rolling resistance because of tire deformation. The loss for a car is approximately 1.0% for every 2 psi (0.1 bar; 10 kPa) drop in pressure of all four tires.[3] Wheel alignment,[4] fuel evaporation while parked,[citation needed] and high engine oil kinematic viscosity,[5] all reduce fuel efficiency.

Mass and improving aerodynamics[edit]

Drivers can also increase fuel efficiency by minimizing transported mass, i.e. the number of people or the amount of cargo, tools, and equipment carried in the vehicle. Removing common unnecessary accessories such as roof racks, brush guards, wind deflectors (or "spoilers", when designed for downforce and not enhanced flow separation), running boards, push bars, and narrow and lower profile tires will improve fuel efficiency by reducing both weight and aerodynamic drag.[6] Some cars also use a half size spare tire, for weight/cost/space saving purposes. On a typical vehicle, every extra 100 pounds increases fuel consumption by 2%.[3] Removing roof racks (and accessories) can decrease fuel consumption by up to 20%.[3]

Maintaining an efficient speed[edit]

A truck restricted to 55 mph

Maintaining an efficient speed is an important factor in fuel efficiency.[5] Optimal efficiency can be expected while cruising at a steady speed, at minimal throttle and with the transmission in the highest gear (see Choice of gear, below). The optimum speed varies with the type of vehicle, although it is usually reported to be between 35 mph (56 km/h) and 50 mph (80 km/h).[7][8][9] For instance a 2004 Chevrolet Impala had an optimum at 42 mph (70 km/h), and was within 15% of that from 29 to 57 mph (45 to 95 km/h).[8] At higher speeds wind resistance plays an increasing role in reducing energy efficiency.

Hybrids typically get their best fuel efficiency below this model-dependent threshold speed. The car will automatically switch between either battery powered mode or engine power with battery recharge. Electric cars such as the Tesla Model S may go up to 728.7 kilometres (452.8 mi) at 39 km/h (24 mph.) [10][11]

Road capacity affects speed and therefore fuel efficiency as well. Studies have shown speeds just above 45 mph (72 km/h) allow greatest throughput when roads are congested.[12] Individual drivers can improve their fuel efficiency and that of others by avoiding roads and times where traffic slows to below 45 mph (72 km/h). Communities can improve fuel efficiency by adopting speed limits[13] or policies to prevent or discourage drivers from entering traffic that is approaching the point where speeds are slowed below 45 mph (72 km/h). Congestion pricing is based on this principle; it raises the price of road access at times of higher usage, to prevent cars from entering traffic and lowering speeds below efficient levels.


Choice of gear (manual transmissions)[edit]


Acceleration and deceleration (braking)[edit]

Fuel efficiency varies with the vehicle. Fuel efficiency during acceleration generally improves as RPM increases until a point somewhere near peak torque (brake specific fuel consumption[15]). However, accelerating to a greater than necessary speed without paying attention to what is ahead may require braking and then after that, additional acceleration. Experts recommend accelerating quickly, but smoothly.[17]



While approaching a red signal, drivers may choose to "time a traffic light" by easing off the throttle before the signal. By allowing their vehicle to slow down early and coast, they will give time for the light to turn green before they arrive, preventing energy loss from having to stop.

When possible, avoid driving during rush hours as the stop and go driving is fuel inefficient and produces more toxic fumes.[18]


Coasting or gliding[edit]



Coasting with a vehicle not in gear is prohibited by law in most U.S. states. An example is Maine Revised Statutes Title 29-A, Chapter 19, §2064[19] "An operator, when traveling on a downgrade, may not coast with the gears of the vehicle in neutral". Some regulations differ between commercial vehicles not to disengage the clutch for downgrade, and passenger vehicles to set the transmission to neutral. This regulations point on how drivers operate a vehicle. Not using the engine on longer precipitous downgrade roads or permanent using the brake might cause a failure due overheating brakes.

Turning the engine off instead of idling does save fuel. Traffic lights are in most cases predictable, and it is often possible to anticipate when a light will turn green. A support is the Start-stop system, tuning the engine off and on automatically during a stop. Some traffic lights (in Europe and Asia) have timers on them, which assist the driver in using this tactic.


Anticipating traffic[edit]


Minimizing ancillary losses[edit]

Using air conditioning requires the generation of up to 5 hp (3.7 kW) of extra power to maintain a given speed.[citation needed] A/C systems cycle on and off, or vary their output, as required by the occupants so they rarely run at full power continuously. Rolling down the windows is often seen as the leading way to prevent this loss of energy. This technique, however, causes increased drag in the form of air resistance and the cost savings is less than is generally anticipated.[20] Using the passenger heating system slows the rise to operating temperature for the engine. Either the choke in a carburetor-equipped car (1970's or earlier) or the fuel injection computer in modern vehicles will add more fuel to the fuel-air mixture until normal operating temperature is reached, decreasing fuel efficiency.[21]

Fuel type[edit]

Using high octane gasoline fuel in a vehicle that does not need it is generally considered an unnecessary expense,[22] although Toyota has measured slight differences in efficiency due to octane number even when knock is not an issue.[23] All vehicles in the United States built since 1996 are equipped with OBD-II on-board diagnostics and most models will have knock sensors that will automatically adjust the timing if and when pinging is detected, so low octane fuel can be used in an engine designed for high octane, with some reduction in efficiency and performance. If the engine is designed for high octane then higher octane fuel will result in higher efficiency and performance under certain load and mixture conditions. The energy released during combustion of hydrocarbon fuel increases as the molecule chain length decreases, so gasoline fuels with higher ratios of the shorter chain alkanes such as heptane, hexane, pentane, etc. can be used under certain load conditions and combustion chamber geometries to increase engine output which can lead to lower fuel consumption, although these fuels will be more susceptible to predetonation ping in high compression ratio engines. Gasoline direct injection compression ignition engines make more efficient use of the higher combustion energy short chain hydrocarbons[citation needed] as the fuel is injected directly into the combustion chamber during high compression which auto-ignites the fuel, minimizing the amount of time that the fuel is available in the combustion chamber for predetonation.

Pulse and Glide[edit]

Pulse and Glide consists of rapid acceleration to a given speed (the "pulse" or "burn"), followed by a period of coasting or gliding down to a lower speed, at which point the burn-coast sequence is repeated.[24][25] Coasting is most efficient when the engine is not running, although some gains can be realized with the engine on (to maintain power to brakes, steering and ancillaries) and the vehicle in neutral.[25] Most modern petrol vehicles cut off the fuel supply completely when coasting (over-running) in gear, although the moving engine adds considerable frictional drag and speed is lost more quickly than with the engine declutched from the drivetrain.

Pulse-and-Gliding (PnG) strategy is proved to be an efficient control design both in car-following[25] and free-driving scenarios,[26] with 20% fuel saving. In the PnG strategy, the control of the engine and the transmission determines the fuel-saving performance, and it is obtained by solving an optimal control problem (OCP). Due to a discrete gear ratio, strong nonlinear engine fuel characteristics, and different dynamics in the pulse/glide mode, the OCP is a switching nonlinear mixed-integer problem.[27][28]

Some hybrid vehicles are well-suited to performing the burn and coast.[29] In a series-parallel hybrid (see hybrid vehicle drivetrain), the internal combustion engine and charging system can be shut off for the glide by simply manipulating the accelerator. However based on simulation, more gains in economy are obtained in non-hybrid vehicles.[24][25]

This control strategy can also be used in vehicle platoon (The platooning of automated vehicles has the potential of significantly enhancing the fuel efficiency of road transportation), and this control method performs much better than conventional linear quadratic controllers.[30]

Pulse and glide ratio of combustion engine in hybrid vehicles points on it by gear ratio in its consumption map, battery capacity, battery level, load, depending on acceleration, wind drag and its factor of speed.

Causes of pulse-and-glide energy saving[edit]

Much of the time, automobile engines operate at only a fraction of their maximal efficiency,[31] resulting in lower fuel efficiency (or what is the same thing, higher specific fuel consumption (SFC)).[32] Charts that show the SFC for every feasible combination of torque (or Brake Mean Effective Pressure) and RPM are called Brake specific fuel consumption maps. Using such a map, one can find the efficiency of the engine at various combinations of rpm, torque, etc.[25]

During the pulse (acceleration) phase of pulse and glide, the efficiency is near maximal due to the high torque and much of this energy is stored as kinetic energy of the moving vehicle. This efficiently-obtained kinetic energy is then used in the glide phase to overcome rolling resistance and aerodynamic drag. In other words, going between periods of very efficient acceleration and gliding gives an overall efficiency that is usually significantly higher than just cruising at a constant speed. Computer calculations have predicted that in rare cases (at low speeds where the torque required for cruising at steady speed is low) it's possible to double (or even triple) fuel economy.[24] More realistic simulations that account for other traffic suggest improvements of 20% are more likely.[25] In other words, in the real world one is unlikely to see fuel efficiency double or triple. Such a failure is due to signals, stop signs, and considerations for other traffic; all of these factors interfering with the pulse and glide technique. But improvements in fuel economy of 20% or so are still feasible.[24][25][33]



Energy losses[edit]

Example energy flows for a late-model midsize passenger car: (a) urban driving; (b) highway driving. Source: U.S. Department of Energy[36][37]




There is sometimes a tradeoff between saving fuel and preventing crashes.[5]


Drafting increases risk of collision[38] when there is a separation of fewer than three seconds from the preceding vehicle.


See also[edit]


  • Jansen. Philip "Driver Influence on the Fuel Consumption of a Hybrid Electric Vehicle: Research on the Fuel Economy Benefits of the Burn and Coast Driving Technique" (Master of Science Thesis) Delft University of Technology, Netherlands. July 26, 2012 PDF
  1. ^ Merriam Webster dictionary
  2. ^ "Motorists risking their lives to save on petrol". 2008-08-23. Retrieved 2011-05-28. 
  3. ^ a b c
  4. ^ "Stretch Your Gas, Mile for Mile". The Washington Post. The Washington Post Company. 2006-05-28. Retrieved 2008-06-03. 
  5. ^ a b c d Diken, Chris; Erica Francis. "Ten fuel-saving tips from a hypermiler". MSNBC. The term was coined by Wayne Gerdes. 'Gerdes isn't just a hypermiler. He's the hypermiler. He's the man who coined the term "hypermiler"' 
  6. ^ "Improving Aerodynamics to Boost Fuel Economy". Archived from the original on 2009-04-12. Retrieved 2009-08-22. 
  7. ^
  8. ^ a b [1] A graph of fuel consumption vs. speed for a Chevy Impala
  9. ^ Modeling Light-Duty Vehicle Emissions Based on Instantaneous Speed and Acceleration Levels, [2], kyoungho Ahn, 2002 Virginia Tech PhD Thesis, Fig. 5-7
  10. ^ Andersen, Ina. " Norske Bjørn kjørte 728 kilometer i en Tesla – på én lading]" Teknisk Ukeblad, 26 August 2015. In English Video on YouTube
  11. ^ "Longest Trip In A Production Electric Car: Tesla Model S P85D breaks Guinness World Records record" World Record Academy
  12. ^ [3] Archived July 19, 2011, at the Wayback Machine.
  13. ^ Panis, L. Int; Beckx, C.; Broekx, S.; de Vlieger, I.; Schrooten, L.; Degraeuwe, B.; Pelkmans, L. (January 2011). "PM, NOx and CO2 emission reductions from speed management policies in Europe". Transport Policy. 18 (1): 32–37. ISSN 0967-070X. doi:10.1016/j.tranpol.2010.05.005. Retrieved March 29, 2014. (Subscription required (help)). 
  14. ^ "Do lower speed limits on motorways reduce fuel consumption and pollutant emissions?". European Environment Agency (EEA). April 13, 2011. Archived from the original on March 29, 2014. Retrieved March 29, 2014. 
  15. ^ a b [4] Typical brake-specific fuel consumption map for a small turbo-diesel.
  16. ^ Julian Edgar. "Brake Specific Fuel Consumption". 
  17. ^ Eisenberg, Anne (2001-06-07). "WHAT'S NEXT; Dashboard Miser Teaches Drivers How to Save Fuel". New York Times. Retrieved 2009-08-22. 
  18. ^ Suzuki, David. David Suzuki's Green Guide. p. 88. ISBN 978-1-55365-293-9. 
  19. ^ "Title 29-A, §2064: No coasting on grade in neutral". Retrieved 2017-10-08. 
  20. ^
  21. ^ "Engines at operating temperature use less fuel". 
  22. ^ "Section 6.13". 1996-11-17. Retrieved 2009-08-22. 
  23. ^ Nakata, K.; Uchida, D.; Ota, A.; Utsumi, S.; et al. "The Impact of RON on SI Engine Thermal Efficiency". Retrieved 2009-08-22. 
  24. ^ a b c d Jeongwoo Lee. Vehicle Inertia Impact on Fuel Consumption ofConventional and Hybrid Electric Vehicles Using Acceleration and Coast Driving Strategy. Ph.D thesis. Virginia Polytechnic Institute, September 4, 2009.
  25. ^ a b c d e f g S. Eben Li, H. Peng. Strategies to minimize the fuel consumption of passenger cars during car-following scenarios. Journal of Automobile Engineering, vol.226, Issue 3, pp.419-429, 2012.
  26. ^ S. Eben Li, X. Hu, K. Li, C. Ahn. Mechanism of vehicular periodic operation for optimal fuel economy in free-driving scenarios. IET Intelligent Transport Systems, vol.9, Issue 3, pp.306-313, 2014.
  27. ^ S. Xu, S. Eben Li, X. Zhang, B. Cheng, H. Peng. Fuel-Optimal Cruising Strategy for Road Vehicles With Step-Gear Mechanical Transmission. IEEE Transactions on Intelligent Transportation Systems, vol.99, pp.1-12, 2015.
  28. ^ S. Eben Li, Q. Guo, L. Xin, B. Cheng, K. Li. Fuel-Saving Servo-Loop Control for an Adaptive Cruise Control System of Road Vehicles With Step-Gear Transmission. IEEE Transactions on Vehicular Technology, vol.66, Issue 3, pp.2033-2043, 2017.
  29. ^ S. Xu, S. Eben Li, H. Peng, B. Cheng, X. Zhang, Z. Pan. Fuel-Saving Cruising Strategies for Parallel HEVs. IEEE Transactions on Vehicular Technology, vol.65, Issue 6, pp.4676-4686, 2015.
  30. ^ S. Eben Li, R. Li, J. Wang, X. Hu, B. Cheng, K. Li. Stabilizing Periodic Control of Automated Vehicle Platoon With Minimized Fuel Consumption. IEEE Transactions on Transportation Electrification, vol.3, Issue 1, pp.259-271, 2016.
  31. ^ Jansen p.18)
  32. ^
  33. ^ Chuck Squatriglia, "Hypermilers push the limits of fuel efficiency" in Wired (Internet magazine) 6 October 2008 [5]
  34. ^ Dennis Gaffney. This Guy Can Get 59 MPG in a Plain Old Accord. Beat That, Punk.. Mother Jones, January/February 2007. Retrieved 2007-05-11.
  35. ^ "Big Rig Drafting". 2008-10-30. Archived from the original on 2008-06-04. Retrieved 2011-03-12. 
  36. ^ "Advanced Technologies & Energy Efficiency". Retrieved 2009-08-22. 
  37. ^ a b
  38. ^ Woodyard, Chris (2008-06-27). "100 mpg? For 'hypermilers,' that sounds about right". Usatoday.Com. Retrieved 2009-08-22. 

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