This resistance is almost completely subject to the factors under driver’s control. Therefore, training and knowledge of the driver becomes very important.

Speed acceleration resistance is subject to the following factors:
- Speed acceleration value,
- Total weight of vehicle

Measures to keep the acceleration resistance low:

Since the acceleration resistance is only affected by the speed acceleration value and the total weight of the vehicle, the saving measures focus on decreasing the instances of acceleration while driving, in other words, unnecessary speeding should be avoided.

Each driver has his/her own responsibility to make use of the vehicle’s own driving speed and driving with foresight.

The driver behind the steering wheel can foresee the upcoming traffic conditions through concentration. Thus, the driver can control his/her own actions (speed up, low down, brake) more effectively along the road and drive safer.

Driving with foresight includes the following factors:

-    Concentrated driving,
-    Smart braking (distance braking – letting the vehicle slow down by itself),
-    Foresee the course of the traffic long in advance,
-    Maintaining adequate distance,
-    Controlled driving,
-    Adjusting driving behavior according to the traffic flow,
-    Making effective use of the road conditions information.

Air resistance is a quite effective resistance. What is interesting is that air resistance is always variable and cannot be controlled completely. Therefore, with regards to decreasing air resistance, factors that should be considered when buying a vehicle and driving the vehicle play a major role.

The amount of air resistance is subject to the following:
-    Speed,
-    Front surface and structure of the vehicle,
-    Streamline of the vehicle (aerodynamic value),
-    Wind direction and force.

Measures that may be taken to keep air resistance low are as follows:
-    Assessment of the road conditions,
-    Choosing the correct range of revolutions per minute,
-    Gear shifting technique (appropriate gear shifting at appropriate time),
-    Assessment of the friction value while buying the vehicle,
-    Selection of the appropriate vehicle height for the intended use.

The sum of friction of the turning wheel,  cruise work,  air friction (on the entire outer surface of the tire) and the  friction in the wheel bearing, constitute the turning resistance of the vehicle wheel.

 Turning resistance of a vehicle depends on the following factors:
-    Speed,
-    Weight of vehicle,
-    Tire type, profile, air pressure,
-    Road conditions.

Measures to be taken in order to keep the turning resistance of the vehicle wheel low:
-    Use snow tires only in winter,
-    Make sure the tie rod is well adjusted,
-    Check the tire pressures regularly (when the tires are cold,if air is used).

Driving with an air pressure less than 2 bars will cause excessive fuel consumption.

Increasing fuel costs and the harmful effects of fossil fuels on the environment increase the necessity of saving fuel by using every means possible. We would like to remind you another measure that will be useful for you to achieve this target that involves minimizing the cruise resistance of vehicles.

We may define the main types of cruise resistance as follows:

1- Turning wheel resistance,
2- Wind resistance,
3- Acceleration resistance,
4- Uphill resistance,
5- Road conditions.

We will try to explain these subjects under separate titles so as to provide some practical advice for you.

Let us try to explain the subject with a formula:
If we perceive the work you are doing as ‘hauling’, let us define the work as carrying the load from point A to B.
Dividing the work by time will give us the efficiency of the work.
Work efficiency is needed to carry the load from A to B within a certain unit of time. Transportation capacity and cruise resistances give the required work efficiency of the engine. Increasing the engine’s work efficiency will return to us as fuel saving. To obtain this, we have to decrease the effect of the cruise resistances.

You might have asked yourself questions such as, "how does this technology work, what are the benefits in developing and using it" about Common-Rail Diesel System Engines that are produced under Euro 3/4/5 norms and used in many of the vehicles that you use. Here you will find a brief explanation about how this technology works.

It has been established that this system is quite stingy in fuel consumption compared to other systems used so far and superior to them in issues such as exhaust emission, silent and noise free operation.

The “Common-Rail” system that can be described as a “high-pressure chamber” lies in the core of this technology. Different from direct drive or single-pump systems used in previous technologies, Common-Rail Technology separates pressure formation and injection. While former diesel-direct injectors operate with pressures of around 175/250-bars, Common-Rail system distributes the fuel to injectors via a common tube under a pressure that may go up to 1600/1800 bars. Injection is provided by magnetic valves located on injectors that prevent time loss. This system offers new possibilities with respect to fuel injection such as the injection pattern and measurement of the amount injected  .

Furthermore, thanks to these possibilities, the system has a great advantage, that is the pre-injection. Pre-injection is performed before the main injection to ensure better combustion of the fuel and it highly improves output rates. Pre-injection or multi-injection is obtained by controlling the magnetic valves many times. Thus, harmful substances, noise emissions, as well as fuel consumption in diesel engines are further decreased.

System pressure is created by a high-pressure piston pump. The pump operates with low drive torques that decrease the load on the pump drive.

Main components of the Common-Rail system are as follows:

1-    High-pressure pump
2-    Common-Rail
3-    Injector
4-    Pressure valves (on injector)
5-    Pressure regulating valve

An electronic control unit on the system regulates this high pressure according to the revolutions per minute and the load of the engine.

Drivers should pay attention to certain issues in order to fully benefit from these advantages made available by manufacturers and to increase the economic service life of the vehicles used.

Accordingly, one should:

1- Have service and maintenance done at trained authorized services.
2- Make sure Diesel fuels that conform to Euro norms are used.
3- Ensure that training is done to allow the necessary knowledge and skills are developed.
4- Obey the mileage requirements for replacing motor oils and use motor oils that conform to the relevant norms.

    The automatic speed adjustment system (cruise control) increases the comfort of the journey when used correctly, but increases the fuel consumption when used incorrectly. In this regard, it has become more and more important especially for the newly produced vehicles that the vehicle be driven by a trained driver who can make efficient use of the technological systems and features employed in the vehicle. The same applies for the cruise control, which is a common feature in all different kinds of bus and coach models. In the following paragraphs, we provide three basic rules that each bus driver should know and apply about cruise control in order to ensure fuel efficiency.

    As a simple fact, the automatic speed adjustment system cannot adjust the vehicle speed by seeing what is ahead. Therefore,

Pay attention to these three golden rules while using the cruise control:

Turn off the cruise control before the peak of an upward slope.

Since the cruise control cannot perceive that the uphill will end soon, the vehicle would continue with ‘full power’ until it reaches the adjusted speed value, after that the vehicle will start to operate the brakes since the road will start to go downhill.
In such a case, the produced energy and momentum gets lost by applying brakes, fuel is consumed abortively, brakes are worn excessively.

If the cruise control is turned off just before the peak, the vehicle passes the peak without acceleration or with very little acceleration and there is little or no need to brake.
Thus the fuel is prevented from being wastefully consumed and the brakes are protected.

If you see that the speed needs to be lowered (for example before a highway exit or if there is heavy traffic ahead) you can turn off the cruise control earlier.

Cruise control cannot foresee that the speed should be lowered beforehand and therefore it keeps the adjusted speed until the clutch and the brake is activated.
Therefore, again the produced energy and momentum gets lost by applying brakes, fuel is consumed wastefully, brakes are worn excessively.

If the cruise control is turned off when the speed is lowered, the vehicle continues towards to the obstacle/bend without acceleration and there will be little or no need to brake.
Thus the fuel is prevented from being wastefully consumed and the brakes are protected.

Do not set the bremsomat speed value (retarder’s automatic activation at the pre-recorded speed) to a value close to the speed value set for the cruise control.

Unlike the cruise control that can automatically activate itself quickly, the retarder cannot automatically deactivate itself as quickly, which can cause a situation where the two systems work simultaneously in opposite directions and clash.

For example, let’s say you are going downhill, the bremsomat is adjusted to 82 km/h and the cruise control is adjusted to 80 km/h. The bremsomat would activate the retarder when your speed exceeds 82km/h, even if the slope of the downhill is very little. Especially when the vehicle is not loaded, the vehicle speed would drop below the limit of 80 km/h rapidly by the retarder, which would in turn activate the cruise control and start acceleration before the retarder fully deactivates.

In this case, the cruise control runs for a short time against the braking effect of the retarder and the fuel is consumed wastefully. To prevent such a waste, there should be at least 5 km/h of `safety distance` left between the speeds adjusted on the cruise control and the bremsomat.

       As a bus driver, you are providing a mentally and physically exhausting and costly service that entails a high level of responsibility. As discussed previously, there are many external factors that affect the efficiency of your work, as well as the overall profitability of your company such as fuel prices, vehicle maintenance costs or the life span of tires. Nevertheless, there are also many factors that you can actually control and turn to your advantage as a driver by being more mindful and applying some simple rules. Practicing these simple rules of thumb will increase the efficiency of your work, lower the costs and increase the profits of your company, and also help protect the environment by decreasing consumption and pollution. All in all, these improvements will definitely benefit you in the form of higher income and higher standard of living.  

As a simple rule of thumb,

Starting and stopping the engine:

-    In a cold engine start, do not press the gas pedal excessively.
-    If possible, start moving right after the engine start.
-    Start moving with the highest gear possible.
-    Avoid heating up the engine in idle running.
-    Check whether the engine reaches the necessary running temperature quickly or not.
-    Try to start an already heated engine without giving gas.
-    Avoid quick starts and very high rpm.
-    Observe the steam exit of the engine.
-    If you need to shut down the engine, do it in idle running, avoid giving gas.

Driving:

-    Shift up right on time to the first or the second next gear. Do not shift gears unnecessarily. Try to use the engine torque to your advantage.
-    Shut down the engine when waiting at the traffic lights or at closed railway crossings.
-    Perform controlled braking.
-    Drive the vehicle within the economical revolution count range (green range). The economical range is 50% - 70% of the engine rpm and 80% at full power.
-    Maintain an engine rpm value suitable for your speed.
-    Apply full power only at the specified rpm and when you need more power (uphill, overtake), this way saving time helps you overall to save more, in spite of the higher level of fuel consumption.
-    Benefit from downward slopes. Before the slope ends, release the brake pedal. Take advantage of the momentum gained by the loaded vehicle.
-    Avoid unnecessary stops; instead of stopping completely, try moving slowly, which will decrease fuel consumption.

       Looking at these simple rules of thumb individually, one could underestimate their effect, thinking “What difference would it possibly make?”. However, applying these rules together as a whole, you will sooner or later see how much difference they can actually make.

The effect of vehicle working conditions
- Warming up the engine in idling
from 0 to 30 degrees Celsius             + 1,3 lit
- Pumping air to a leaking air pressure instalment from 0 until the closing pressure level
1400 rpm                                            + 0,6 lit
- Warming the vehicle interior by running the engine
Vehicle engine consumption
Appr.  2,0 – 3,0 lit/hr                            +2,7 lit
Additional consumption of the heater
Appr.  0,3 lit/hr

The effect of maintenance conditions

- Dirty air and fuel filters.
- Broken or out-of-tune fuel injector pump (except for CR engines).
- Using inappropriate oils (e.g too thick oil).
- Excessive oil levels.
- Non-calibrated braking system (e.g tight brake linings).
- Defective wheel bearings.

These factors in total increase the fuel consumption between 2% and 4%.

Next topic: Driving tips

• - Appropriate selection of the engine technology used in the vehicle.
  
• - Selecting of the appropriate transmission for the intended conditions of use.
  
• - Selecting a differential with the right ratio to suit the intended conditions of use.
  
• - Selection of drivers trained on economic vehicle usage.
  
• - Good maintenance by trained and authorized service personnel.
  
• - Use of vehicle with foresight.
  
• - Employing trained drivers who can easily use the technological systems installed in the vehicles.
  
• - Efficient use of auxiliary tools like the retarder and the cruise control (tempomat).
  
• - Qualified vehicle maintenance.
  

These factors in total will help you reach the following results:

- 25% savings in fuel consumption
- 15% increase in speed
- 45% decrease in shifting gears

Next topic: Vehicle working and maintenance conditions

         There are a number of factors affecting how one can achieve savings in fuel consumption, as summarized in this series of articles. The values here are given as a reference for estimation purposes. While making your calculations, do not sum up the individual percentage data, but always start with a new base value to calculate the fuel consumption. As a final rule of thumb, start your vehicle every time by saying “I am a novice driver" and try to implement all the mentioned tips and advice.

Variable                                                                                        Change in fuel consumption

Vehicle height                                                                              
At 80 km/h 4,0m                                                                                       0% (assumed)
3,5m                                                                                                       - 5%

Tire selection
Normal road tire                                                                                         0% (assumed)
Highly road resistant tires (each tire)                                                           - 5%

Tire pressure that is 2 bars lower than the normal value                           (Each tire) + 0,5%

1 degree of distortion in the movement of the vehicle                                 + 5%

Vehicle weight
25 tons                                                                                                     + 5%
20 tons                                                                                                       0% (assumed)
15 tons                                                                                                     - 5%

Rear axle shaft type
Hypoid axle shaft                                                                                          0% (assumed)
AP Axle / Outer Planet                                                                               + 2%

Axle ratio
10% shorter than the needed value                                                             + 2%
20% shorter than the needed value                                                             + 5%

Mileage
0 Km                                                                                                         0% (assumed)
50,000 Km                                                                                               - 5%

External air temperature
- 10 Degrees Celsius                                                                                  + 5%
+ 10 Degrees Celsius                                                                                    0% (assumed)
+ 30 Degrees Celsius                                                                                  - 5%

Wind
Strong wind                                                                                             + 10%
Weak wind                                                                                                  0% (assumed)
No wind                                                                                                    - 5%

Rain
Dry Road                                                                                                    0% (assumed)
Humid Road                                                                                              +2%
Wet Road                                                                                                 +5%

Road type/conditions
Straight highway                                                                                        - 30%
Complex long road                                                                                        0% (assumed)
Heavily ramped road                                                                                  + 20%
Local-city road                                                                                          + 100%

Driving style
Highly economical driving                                                                             - 5%
Economical driving                                                                                       0% (assumed)
Non-economical driving                                                                               +10%