Research Trends and Results

Improving methods of predicting change of emissionsof carbon dioxide from automobiles as roads open forservice
KADOYU Katsunori, Head
OGAWA Tomohiro, Senior Researcher
NAGAHAMA Yosuke, Researcher
Road Environment Division, Road Department(Key words) Road, carbon dioxide, technical method of evaluating road environment impact
1. Introduction
The development of methods of predicting changeof greenhouse effect gas emissions accompanying
road projects has, until now, been done by various
administrative bodies and research institutes insideand outside of Japan, but, a standard method which aroad builder can practically apply at the road plan
study stage has not been established.
So studies have been carried out to complete
knowledge concerning the range of the impact ofchanges of traffic flow and of the emissions of carbon
dioxide (below, “CO2”) when a new road opens totraffic, and to overcome challenges to improving
methods of predicting the range of such impacts.
2. Study method
Fifteen actual road plans (5 cases each of bypass,
expressway, and ring road projects) were used to trial
calculate change of traffic volume, traveling speed,
and CO2 emissions caused by the opening of a newroad to service and to analyze the state of thesechanges, based on the CO2 emission coefficient by
estimated traffic volume and by travel speed.
Figure 1. Distribution of Change of CO2 on the New
Road and Surrounding Roads (Example of a bypass road,yellow shows the project location)
ChangeCO2CO2of変化

National highway
国道 145 145号
National highway
国道 17 17号

35km range
Change of CO2 emissions
Reduced more than 10%
Reduced 5 to 10%
Reduced 2 to 5%
Changed from -2 to 2%
Increased 2 to 5%
Increased 5 to 10%Increased more than 10%

Figure 2. Distribution of Change of CO2 on the New
Road and Surrounding Roads (Example of a ring road,yellow shows the project location)
ChangeCO
2 変化 of CO2

Change of CO2 emissions
Reduced more than 10%
Reduced 5 to 10%
Reduced 2 to 5%
Changed from -2 to 2%
Increased 2 to 5%
Increased 5 to 10%
Increased more than 10%
Road network

3. Results of the study
Figure 1 and Figure 2 show examples of the changeof CO2 emissions accompanying the change of traffic
volume on the new road and on surrounding roads.
They show that while the traffic volume increaseson the new road and sections at each end, on multiple
roads parallel to the new road, the traffic volume falls
accompanied by a decline of CO2 emissions. As aresult of analyzing such changes in traffic volume andCO2 emission in detail, the following were obtained as
criteria for the range of the evaluation of the newroads.

National
国道292 号highway 292

Bypass:for 10km of improved road, areal range of about 30
to 40km
Expressway: areal range on the inside of a distance of 50km ormore. It is also effective to narrow the focus toexpressways and national highways.
Ring road: wide areal area such as an entire regional block.

Research Trends and Results
But in the future, the criteria must be verified bycomparison with actual changes caused by the openingof a new road.
4. Summary
The successful results and knowledge provided by
the study will be further verified in the future, and willcontribute to the building of a method of predicting
CO2 emissions of road projects.