Assessing the impact of Medan-Stabat toll road on carbon monoxide pollutant in arterial roads

Carbon monoxide is the result of the combustion of motorized vehicles which can pollute the air and will cause negative impacts to the health of human beings. The development of a toll road is initiated in the routes of an arterial road which have been causing congestion or terrible traffic jams, and is expected directly to reduce the amount of traffic jams and to increase the speed of travel, and indirectly to reduce air pollution in the arterial roads. The objective of this paper is to predict the effects of the Medan-Stabat Toll Road operation to the CO pollutant contents in the arterial roads. The results indicate that the level of pollution is reduced up to 10 % and 25% due to traffic shifting on the arterial roads to the toll road.


Introduction
Air contamination has changed the natural characteristics of the atmosphere which have been caused by chemical, physical or biological materials from both natural processes and human activities who have been fulfilling their needs both in the production and in the transportation sector [1].The contribution of the transport sector to carbon monoxide (CO) pollutants has been proved by many previous research [2].According to World Research Indonesia in 2018, land transportation contributes approximately 46% of the entire air pollution, then the industrial sector which also has contributed approximately 43% of the air pollution.Air contamination as a result of industrial and transportation activities will cause negative impacts to the ecosystem [3].
The objective of toll roads development in Indonesia is to increase regional connectivity in order to support the logistic sector.Until 2022, Indonesia has operated 69 toll highways as long as 2,578 km [4].The development of a toll road in general is initiated in the routes of an arterial road which has caused a congestion or has a high traffic, with the objective to shift the traffic from the arterial road to the toll road.Therefore, the operation of a toll road is expected directly to reduce the load of traffic and increase the travel speed, and indirectly reduce air pollution in the arterial roads due to the active operation of the Medan-Stabat Toll Road.This paper aim is to predict the influences of the Medan-Stabat Toll Road operation to the CO pollutant contents in the arterial road.The limitation of this paper does not consider changes in average speed on arterial roads due to the Medan-Stabat toll road not operating.
The emission of CO which derives from transportation activities can be calculated by using the vehicle volume approach, and the type and speed of the vehicle [5].Therefore, it is identified the aggregation value of the pollutant formed in CO data is expected to provide information for the stakeholders, and will be the basic consideration of developing the toll road towards the quality of air in the future.

Environment impact of road transportation
Emission is a substance resulted from a certain activity which enters the ambient air and has a potential aspect as a pollutant.After having been evaluated from the effect to the perspective of public health, The main toxic pollutant is emitted to the environment from the fuel combustion which contains carbon monoxide (CO), nitrogen dioxide (NO2), hydrocarbon (HC) and particulates (PM).The land transportation sector has contributed 18% of the total amount of CO pollutants [6], which contains high concentrated substances that contains toxic substances [7].Along with the economic growth, transportation activities which have been developed rapidly and significantly may cause air pollution [8] [9].The most amount of pollutant caused by motorized vehicles is CO, as a result of fuel combustion.The highest calculated concentration of CO pollutant at distance 20 m from the road [10] and will be the main source of contamination in the urban areas [11].
The Emission Factor is one value which has described the relationship between the quantity from the emission released by the air with a certain activity related with the source of pollutant [12].These factors usually are usually acknowledged as the weight of the pollutant, such as illustrated in the table below.
Table 1.The emission factor based on the type of vehicle [12].

Types of Vehicles
Emission Factor (grkm

Predictive Models of Carbon Monoxide Pollutant
To predict the emission of the vehicle released by the vehicle considers many factors such as the surrounding air temperature, the length of the journey, the type of vehicle, the age and the fuel used and the speed of the vehicle.Many Prediction Models have been initiated based on the solid correlation between the use of fuel with the content of emission, because the fuel will be one main agent in the process of combustion [14].The relationship between fuel and emission is acquired from the empirical data from the developed nations, where in several cases of certain pollutant emission will not depend physically to the consumption level of the fuel [15].ETSU (1997) which has also created an equation below to predict the emission related with the speed of the vehicle: Indonesia has applied a guideline in predicting the size of emission which is the Line Source Model and the Osaka Municipal Government [16].The Line Source Model is based on the assumption that the emission of pollutants in the highway is unlimited until every dot has a similar distance from the side of the road and will receive pollution with the equal amount of concentration, with the equation as written below.The model which has been adopted considers the number of vehicles and the speed of the vehicles which has a close relationship with the concentration of pollutants.The model selection is based on the height and density of the construction.

Methodology
After Medan-Stabat toll road is operated, the traffic in arterial road will shifting into the toll road.The idea is to predict the impact of diverted traffic on vehicle emission in the arterial road, by using the scenario with or without toll road operated.The research location of the Soekarno-Hatta and Tengku Amir Hamzah arterial roads with the consideration is the arterial roads which exists on the side of the Medan-Stabat toll road.
On both the arterial roads, the average height of a building could reach 8.2 meters with a density rate of 0.831, based on that matter the prediction of a CO gas emission will use a Lined Source Model Equation.
In this research a scenario is conducted with and without the operation of the Medan-Stabat toll road, The size of reducing the emission of CO pollutants on the arterial road is assumed to reduce caused by the shifting of vehicles from arterial road to the toll road.In order to identify the concentration of CO pollutant on both the roads, an equation is required [16]: 1.The CO emission rate, which can be acquired by including the average speed of the vehicle to the roads with an equation as elaborated below:  = 867.92−0.8648 Where: q : The flow of emission (gr km -1 ) V : The average speed of the vehicle (km hr -1 ) 2. The CO emission force (Q), is the mass of the pollutant that is dispersed from the source of emission per unit of time.The Volume of Vehicle evaluated is the volume during the peak hour with the type of large vehicle equivalent to the passenger loaded -vehicle.The size of the emission can be acquired from the equation mentioned below: Where: Q : The CO emission force (gr sec -1 ) n : The number of vehicles per second q : The Flow of emission (gr km -1 )

Result
The basis of traffic analysis were data collected directly on T. Amir Hamzah and Soekarno-Hatta streets (arterial road) and Medan-Stabat toll road.The Analysis on the traffic volume during the on-peak hours with the composition of the vehicles (Light Vehicle with < 2800 CC and Heavy Vehicle > 3000 CC).The volume during the on-peak hours of each category of the vehicle is equivalent to the unit of passenger loaded-vehicles furthermore will be normalized with the emission multiplication factor.The CO emission rate is the size of pollutant masses released by one vehicle per kilometre and acquired by including the variable of the average speed of the vehicle to the roads predicted by the equation ( 5): The CO emission force during on-peak hours is acquired by using the equation ( 6), can see in the table below: From the table above, it is identified that the total of CO emission force for the Soekarno-Hatta Street with the amount around 29.954 gr s -1 For the Tengku Amir Hamzah Street is with the total of CO emission force amounts up to 15.866 gr s -1 .For the Medan-Stabat toll road the amount of CO emission force amounts up to 5.323 gr s -1 .
The concentration of pollutants is the amount of contaminated substance released to the air by the traffic within the volume unit.In order to identify the amount of concentration of the CO pollutants on each road, an equation is applied (6), with the results of the calculation elaborated below: The concentration of CO pollutants in the arterial roads amounts up to 11,373 μg m -3 and 3,909 μg m -3 .The concentration of the CO pollutants without the operation of the toll road amounts up to 12,685 μg m -3 and 5.221 μg m -3 , is acquired with the assumption that the concentration of CO pollutants in

Figure 1 .
Figure 1.Emission based on the type and speed of the vehicle [13].
An, et al. (1997) has created an equation to predict the CO pollutant which has been released by the vehicle with an equation as mentioned below. =    (1) Where: EOECO : engine out CO-emission (gr km -1 ) aCO : constant (gCO gFuel -1 ) FC : fuel consumption (gr km -1 ) emission in gkm -1 i : Type of emission (which are HC, CO, NOX, SO2, Pb, PM or CO2) a1 until a6 S : Model parameter which varies based on the type of emission and S : The speed of the vehicle in km hour -1 of pollutant (gr m -3 ) Q : Emission force (gr s -1 ) H : The height in the source of emission (m) (x,y,z) : Receptor coordinates  : Deviation standards z : 1.5 m, in the disperse case  0 (ground level) y : 0, y  1The Osaka Municipal Government (OMG) Model has mentioned the emission released by the motorized vehicle in on road as an imaginary volume which flies above the surface of the road.

Figure 2 .
Figure 2. The Imaginary Pollutant Volume above the surface of the road [16].

Table 2 .
Traffic volume and average speed

Table 3 .
Normalizing traffic volume with emission multiplier.

Table 4 .
CO emission rate of each vehicle.

Table 6 .
Total concentration of CO pollutants.