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The vehicular emissions are due to a variety of factors.
The emissions vary according to the environment, fuel quality, vehicle, etc.
emissions are higher in congested and urban areas.
Fuel adulteration and overloading also cause higher amount of emissions.
The emissions from vehicles depend on the following factors:
- Travel related factors
- Highway Network related factors
- Vehicle related factors
The number of trips, distance travelled and driving mode are the major travel
related factors affecting emissions.
As the number of trips increases, the amounts of emissions also increase.
Emissions increase with the distance travelled by the vehicle.
The vehicular emissions also depend on the driving mode.
The driving modes may be idling, cruising, acceleration and deceleration.
These modes complete one driving cycle.
Other factors affecting the emission rates are the speed, acceleration and
engine load of the vehicle.
Low speeds, congested driving conditions, sharp acceleration, deceleration,
etc. result in higher emissions.
On the other hand, intermediate speeds and low density traffic conditions cause
lower emissions.
These include the geometric design features of the highway such as grade.
The emission rate is very high at steep gradients, as the vehicle needs to put
in more effort to maintain its speed.
The highway network facilities such as signalized intersections, freeway ramps,
toll booths, weaving sections, etc. also influence the vehicular emission
rates.
Vehicle related factors include the engine sizes, horsepower and weight of the
vehicle.
Vehicles with large engine sizes emit more pollutants.
Since larger sized engines are seen in vehicles with more horsepower and more
weight, these factors also contribute to the emission rates.
Another important factor is the age of the vehicle.
Older vehicles have higher emission rates.
- Ambient Temperature:
Evaporative emissions are higher at high temperatures.
- Type of engine:
Two stroke petrol engines emit more amounts of pollutants than the four stroke
diesel engines.
- Urbanization:
Congestion is higher in urban areas, and hence emissions are also higher.
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