Transport, and road transport in particular, is a major consumer of finite fossil fuel resources. Furthermore, the CO2 emissions from fossil fuels are widely recognised as highly environmentally damaging. Large-scale substitution by alternative fuels will not take place in the short to medium term due to institutional barriers. Therefore, fuel conservation, i.e. performing the same (or similar) transport task with the use of less fuel, is a sensible interim strategy.
The largest potential to reduce fuel consumption in road transport probably lies in enhancing vehicle technology. However, such an approach involves a relatively long implementation time and considerable costs. Inducing a change in driving behaviour is an effective way to reduce fuel consumption in the short term. Research has revealed that a 15% reduction in fuel consumption possible by changing driving behaviour. An additional benefit of aiming at a change in driving behaviour is that much of the improvement achieved will still be valid when new vehicle technology becomes available. Together they can reduce fuel consumption even further.
Although it is clear that driving behaviour has a significant bearing on fuel consumption, it is often unclear how one should drive in order to minimise fuel consumption. Feedback helps to obtain insight in the impact of one's actions on fuel consumption. A driver support tool provides the driver with direct feedback in the vehicle. Several driver support tools were developed, after the first oil crisis in 1973/1974, to directly or indirectly improve fuel economy. However, tests with these devices revealed that none of the devices was able to bring about the levels of fuel reduction judged possible due to some major shortcomings.
The objective of this research was to design a fuel-efficiency support tool that significantly reduces fuel consumption by inducing a directed and consistent change in driving behaviour and to evaluate the new fuel-efficiency support tool with respect to its objective as well as requirements from safety, traffic performance and environmental perspective.
Learning from the shortcomings of existing devices and addressing
the limits of the driver, it was concluded that for a driver support
tool to significantly reduce fuel consumption, it should:
· provide the driver with clear, accurate and non-contradictory
information at the right moment
· take into account the context a vehicle is in
· place no requirements on the driver that are too high
to combine with the actual driving task
· work within both an urban and non-urban environment.
Furthermore, there should be a clear causal relationship between
the driver's actions and the support obtained and the driver should
not be overloaded by the amount of support provided.
A fuel-efficiency support tool has been designed that takes
into account all the requirements for an effective support tool.
In the design process, focus was placed on passenger vehicles
with a petrol engine and a manually operated transmission, since
they represent the largest energy consumer within road transport
in Europe. The design process resulted in a new fuel-efficiency
support tool that:
· gathers information from the vehicle and its surroundings
· identifies the present context of the vehicle
· calculates the optimal driving behaviour to minimise
fuel consumption within this context
· compares actual driving behaviour with this optimal behaviour
· generates advice if a significant deviation occurs
· presents advice to the driver, if the timing and contents
of the advice is safe and suitable, on how to change driving behaviour
in order to minimise fuel consumption.
The new fuel-efficiency support tool provides clear and direct advice on how to change driving behaviour in order to reduce fuel consumption. The advice is presented to the driver by means of a human-machine interface. Four interfaces were designed for the new fuel-efficiency support tool that differ with respect to the length of advice, i.e. brief or detailed, and the modality of presentation, i.e. visual or auditory. One of the aims of the evaluation process was to reveal which of the four interfaces accommodates the limits of the driver best.
The evaluation process was divided in three stages. During
the first two stages the interaction between the support tool
and the driver was evaluated by means of a driving simulator experiment
and a field experiment respectively. During the third stage, the
outcome of the driving simulator and field experiments was placed
in perspective by evaluating the impact of the interaction between
support tool and driver on its surroundings. In the evaluation
process the new fuel-efficiency support tool was evaluated with
respect to:
· its most suitable human-machine interface
· its fuel reducing capability
· the workload placed on and acceptance by the driver
· the induced change in driving behaviour
· its impact on network level
Most suitable interface
The driving simulator provided a safe environment in which the
four interfaces could be compared under the same, controlled circumstances
in order to select the most suitable interface. The interface
presenting detailed advice visually to the driver is concluded
to be the most suitable interface. Visual presentation was judged
less irritating and distracting, whereas detailed advice was found
easier to understand and caused drivers to drive significantly
more fuel-efficiently than without support.
Fuel reducing capability
The fuel reducing capability of the new fuel-efficiency support
tool was compared with no support and existing devices. Both experiments
revealed that the new fuel-efficiency support tool significantly
reduces fuel consumption compared with no support and the existing
devices. Under real traffic circumstances (i.e. during the field
experiment), drivers reduced fuel consumption on average by 11%
with the help of the new fuel-efficiency support tool compared
with their normal driving behaviour. A fuel reduction of only
6% was obtained with the help of the existing device, whereas
drivers receiving no support were able to reduce fuel consumption
by 7% as a result of practice.
The largest fuel reducing capabilities of the new fuel-efficiency support tool were found over the urban section of the route. Over the urban section participants were able to reduce fuel consumption by 20% compared with normal driving. As opposed to existing devices, the new fuel-efficiency support tool works in both urban and non-urban environments. It actually works even better in the urban environment where most fuel can be saved.
The fuel reducing capability of the support tool was assessed over a 2.5-day period. The assessment revealed that drivers kept learning from the support tool how to change driving behaviour in order to reduce fuel consumption. It is expected that the reduction in fuel consumption will increase if the support tool is available for a longer period. In addition, it was found that with the new support tool drivers were able to overcome the impact of higher traffic volumes on fuel consumption, whereas with the existing device drivers could only limit the impact compared with no support.
Overall, it is concluded that, as opposed to existing devices, the fuel-efficiency support tool is able to induce fuel consumption reductions that exceed the levels of fuel reduction judged possible based on literature, i.e. a 15% reduction over a (sub)urban route.
Workload and acceptance
Workload perceived by the driver was measured to assess whether
the fuel-efficiency support tool could be safely combined with
the actual driving task. The assessment revealed that the support
tool placed extra demands on the driver compared with no support
or existing devices. However, the perceived workload never exceeded
the level of rather present mental effort. Therefore it can be
concluded that the fuel-efficiency support tool can be safely
combined with the actual driving task.
Furthermore, a fuel-efficiency support tool can only be actually effective if it is accepted by the driver. Questionnaires revealed that the advice of the fuel-efficiency support tool is appreciated by the drivers. After driving with the support tool, drivers expressed that they found the support tool even more useful than they had expected. The advice was most valued in the urban and rural environments.
Changed driving behaviour
The significant reduction in fuel consumption is caused by a change
in driving behaviour as a result of the advice from the new fuel-efficiency
support tool. Analysis of driving characteristics recorded during
the driving simulator and field experiments revealed that the
change in driving behaviour due to the support tool can be described
by three aspects:
· Drivers have a smoother driving style and anticipate
better to oncoming traffic situations, which is expressed by a
reduction of quick variations in speed and large accelerations
and decelerations. The driving simulator experiment revealed in
addition a reduced occurrence of small Time-to-Collisions.
· Drivers adapt their gear changing behaviour: with the
support tool, drivers change earlier to a higher gear and remain
longer in this gear. The time that is driven in 5th gear is significantly
extended when drivers are assisted by the support tool. During
acceleration, drivers also change early to a higher gear.
· Drivers turn off the engine more often when they are
standing still.
It should be noted that average speed was not affected by the
fuel-efficiency support tool, since drivers were asked, and managed,
to keep average speed constant. It means that with the fuel-efficiency
support tool drivers significantly reduced fuel consumption without
increasing travel time.
Network effects
The outcome of the driving simulator and field experiments was
placed in perspective by assessing the network impact of the interaction
between support tool and driver on traffic performance, traffic
safety, fuel consumption and emissions.
The new fuel-efficiency support tool combines the benefit of inducing large reductions in fuel consumption with good indications of stabilised traffic flow and improved traffic safety due to the increased anticipation of drivers to oncoming situations.
The impact of the fuel-efficiency support tool with respect to fuel consumption and emissions on network level is equal to the sum of the impacts found for the individual vehicles equipped with the fuel-efficiency support tool in a network, due to the minimally affected interaction between vehicles. The reduction in fuel consumption caused by the fuel-efficiency support tool per individual vehicle seems to be half due to the increased anticipation by the driver and the smoother driving style and half by the improved use of engine efficiency through the adapted gear changing behaviour. On emissions the fuel-efficiency support tool likely has a positive effect. Especially carbon dioxide emission is directly related to fuel consumption and therefore significantly reduced by the support tool.
Finally, it is concluded that the objective of the research project has been achieved: A fuel-efficiency support tool has been designed that has proven to reduce fuel consumption significantly by inducing a directed and consistent change in driving behaviour. Average reductions in fuel consumption of up to 20% were obtained without increasing travel time. In addition, the new fuel-efficiency support tool revealed to be safe and is expected to stabilise traffic flow and reduce exhaust emissions.