Intersection management: air quality impacts

Transcription

1 Intersection management: air quality impacts M. El-Fadel/') H. Sbayti,^ M. Abou Najm^^ Department of Civil & Environmental Engineering, American AW For/r, 7V , Ib ^ Department of Civil & Environmental Engineering, American f.o. 5ox; / 7 04 j, ^ Department of Civil & Environmental Engineering, American [/^zw^zyyc/g^zn/r, f.o. Box; /2020, mra02(a)aiib. edu. Ib Abstract Urban areas of Beirut suffer severe traffic congestion because of a deficient transportation system resulting in economic losses and adverse environmental impacts. Grade separations are proposed at several intersections to minimize this problem. Air quality, which highly depend on the geometric configuration of an intersection, is a major environmental concern. This paper presents an air quality impact assessment at a typical intersection where a grade separation is proposed. For this purpose, computer simulations were conducted to define concentrations in the air of selected pollutants. Simulations were performed for worst case scenarios including with and without grade separations and changes in vehicle mix. The assessment of the impact significance of air emissions was then conducted by comparing the predicted pollutants concentrations with baseline air quality levels and relevant air quality standards with the objective of optimizing the intersection management in terms of minimal air quality impacts.

2 84 Urban Transport and the Environment for the 21st Century Introduction The transportation sector is the largest contributor to urban air pollution in Lebanon considering the rapidly increasing vehicle fleet and the absence of heavy industries (El-Fadel and Bou Zeid\ Staudte et a//). The residents of the Greater Beirut Area (GBA) are exposed to elevated concentrations of air pollutants especially in periods of hot summers which are characterized with minimal air circulation and high humidity. The sensitivity of pollutant levels to changes in the geometric and operational setup of a typical intersection for worst case conditions is explored in this paper. Mathematical simulations were conducted to determine the effects of geometric changes in the intersection and vehicle fleet improvements on pollutant concentrations. Long term strategies for proper air quality management are proposed to insure beneficial formulation of future transportation policies with respect to urban air pollution. Existing Conditions Existing data on air quality in the GBA are practically non-existent (Shaaban and Ayoub^). Air samples were collected at several intersections designated for a grade separation proposed as a component for traffic management in the GBA. The samples were analyzed for selected constituents. Measured concentrations in air of most constituents exceeded international standards (El-Fadel et a//). Many factors prevailing in the GBA are conducive to high levels of pollution: (1) poor level of service of existing roadways; (2) absence of regulations concerning vehicle emissions; (3) weak and unreliable public transport system; (4) relatively old vehicle fleet; and (5) fuel quality. Vehicle Fleet Characteristics The Lebanese fleet is comprised mainly of passenger cars and characterized by relatively old and poorly-maintained vehicles (Table 1). Although predictions indicate a decrease in passenger cars and an increase in bus trips as a result of introducing a mass transit system (TEAM^), it is unlikely that this will occur in the near future because of: (1) minimal changes in the fuel taxation policy; (2) weak urban planning practices; (3) lack of enforcement of traffic regulations; and (4) socio-cultural stigma associated with bus riding. Table 1. Vehicular mix of traffic fleet (TEAM*) Vehicle Type Fleet (Percent) Occupancy (Persons) Cars Medium trucks 6 3 Heavy trucks 2 1 Buses 2 10

3 Urban Transport and the Environment for the 21st Century 85 Definition of Applicable Air uality Standards Ambient air quality standards have been proposed in Lebanon within the 1994 Urgent Draft Law (never implemented) which specified concentration levels for the prevention of air, water and earth pollution. These standards seem to be political or administrative settings only. No scientific program was followed to develop these standards (Staudte et a/7). The limit values are lower than international standards and seem to be unreachable. As a result, these standards cannot be used for assessment purposes. Instead, it is more appropriate to use international standards (Table 2). Table 2. Selected Lebanese and international standards Pollutant CO NOi TSP Lebanese Standards /#//?/ (/%?m) 10,000(9) 120(0.0063) 120 a. World Health Organization b. Environmental Protection Agency c. European Union International Standards Concentration /#//,/ #%?/%; 30,000 (27) 10,000(9) 10,000(9) 400(0.21) 200(0.1) 100(0.05) Averaging Period 1 hr. 8hr. 8hr. 1 hr. Ihr. 1 hr. 24 hr. 24 hr. Source WHO* WHO EPA* WHO Elf EPA WHO EPA Modeling Methodology Air emissions are a function of the expected traffic conditions (volume and speed) and meteorological conditions at a particular location as well as the fleet characteristics. Air quality dispersion modeling was used to estimate pollutant exposure levels at selected locations around a typical intersection (Figure 1). Potential sources (congested roads) coupled with least favorable meteorological conditions (AUB^) are used to simulate the worst-case exposure scenario. The mathematical model CALINE4 was applied to predict pollutant concentrations in the air. The model uses the sub-model EMFAC, to estimate composite on-road emission factors (ARJB*). Figure 2 presents a flow diagram of the modeling methodology and the parameter required for this process.

4 86 Urban Transport and the Environment for the 21st Century Figure 1. Intersection layout Sensitivity Analysis measures for improvement of air quality by means of geometric and fleet improvement scenarios CALINE4 Air Pollution Simulation Model Pollutants Concentrations Fleet Characteristics Traffic Data Air uality Air uality Standards Limiting Values Selection of the Optimum Solution Figure 2. Methodology flow diagram Model Simulations Model simulations were conducted to evaluate changes in gometric configuration and vehicle mix at a typical congested intersection. Geometric changes consists of the construction of a grade-separation (overpass/underpass) to accomodate the heaviest traffic in the East-West direction running both ways (Figure 1). Vehicle mix was modified assuming the implementation of a mass transit system.

5 Urban Transport and the Environment for the 21st Century 87 Type of Grade Separation Grade separation is an effective transportation strategy aimed at increasing the average cruising speed and hence reducing traffic delays at an intersection. Although its primary function is for traffic management, a grade seperation may help in reducing pollutant concentrations in the air because of less stop-and-go traffic and increased vehicle speed. Emission factors increase significantly in stop-and-go traffic because of the acceleration and deceleration processes wich can result in 5 to 10 fold increase in emissions (Faiz et al.*). Increased average crusing speed on the other hand can reduce emission factors significantly (Figure 3). Note however, that there is an upper limit of 35 and 55 mph above which emission factors start to increase again for NO% and CO, respectively. In addition, by virtue of its elevation, an overpass would reduce exposure to air pollutants at ground level due to the increased dilution time. Similarly, an underpass confines air pollutants and hence, reduces exposure to air pollutant concentrations at ground level particularly in the presence of an effective ventilation system. 300 Speed (mph) Speed (mph) Figure 3. Emission factors variation with speed at 30 C Concentrations of CO and NO* were simulated for the year 2010 for two scenarios: (1) do nothing; and (2) construct a grade separation (overpass or underpass). The simulated CO and NOx concentrations for the do-nothing scenario exceeded the WHO standards (Figure 4). The introduction of a grade seperation reduces the concentration in air of both CO and NOx. The reduction in CO concentration reached 37 and 47 percent for an overpass and an underpass, respectively. The reduction in NOx concentration was less significant and reached 2.5 and 30 percent for an overpass and underpass, respectively. Note that while the construction of a grade seperation reduces CO concentrations to below the WHO standards (Figure 4), NO% levels remained above these standards. This can be attributed to the fact that NOx emission factors increase at a greater rate beyond an average crusing speed of 35 mph (Figure 3).

6 88 Urban Transport and the Environment for the 21st Century _ o Annn 1 251"i No Design Overpass Underpass ] _ & 600 =L z No Design Overpass Underpass Figure 4. Effect of a grade separation on air quality Vehicle Fleet Mix Vehicle mix can have a significant effect on air quality especially due to the presence of heavy vehicles (trucks and buses) at peak hours. In urban areas, traffic congestion and volume reduction are accomplished through extended usage of mass transit systems. Such usage can change the vehicle mix and hence the extent of pollutants emissions. In the GBA, the vehicle fleet is composed of 90 percent passenger cars (Table 1). A traffic demand analysis indicates that the ridership share of a recently established public bus transport system has reached 11 percent (El-Fadel et al*). The implementation of regulations and policies encouraging the use of this system can easily double this share to 22 percent reducing the traffic volume fleet by 11 percent and increasing the average cruising speed by 5 kph. More stringent regulations can even triple the mass transit ridership share to reach 33 percent reducing the traffic volume by 22 percent and increasing the average cruising speed by 10 kph. Certainly the vehicle mix would vary if bus ridership is doubled or tripled. The corresponding fleet volume reduction reaches 11 and 22 percent, respectively (Table 3). Table 3. Vehicle mix of various scenarios Vehicle Type Cars Medium rucks Buses Heavy trucks Volume reduction Alternative 1 Bus Ridership /7% Alternative 2 Bus Rides hip 22% % Alternative 3 Bus Ridership 33% %

7 Urban Transport and the Environment for the 21st Century 89 Simulations results for the three alternatives are described in Figure 5. The change in vehicle fleet mix reduced CO concentrations because of: (1) traffic volume reduction; (2) increase in speed and; (3) change in emission factors. The interrelationship between these factors and emissions is shown in Figure 6. The reduction in CO concentrations at the predefined receptor locations reached 32 and 55 percent for alternatives 2 and 3, respectively. For NO% emissions, the situatiuon is more complex because the increase in NO* emission factors start at an average speed of 35 mph compared to 55 mph for CO. The increase in speed and the reduction in traffic volume for alternative 2 did not reduce NO% concentrations. This can be attributed to the elevated emission factors associated with heavy vehicles thus leading to an increase in NO% concentrations. Moreover, the reduction in traffic volume and the corresponding speed increase in alternative 3 had a more pronounced effect on NO* concentrations than the increase in emission factors. This results in a net decrease n concentrations. Nevertheless, the net reduction is not significant enough to reduce the NO% level below the WHO standards i ^ m "Sb 3 MM o ^ ' I 0 - Alternative Alternative Alternative P Iw * j ] " Hi Alternative 1 Alternative 2 Alternative 3 Figure 5. Effect of vehicle mix on air quality Change in vehicle mix due to increase in percent of busses Net traffic volume reduction 1. Increase in bus percent 2. Decrease in passenger cars Change in fleet emission factors: 1. Increase due to increase in bus percent 2. Decrease due to increase in speed <35 mph for NO, <55 mph for CO 3. Increase due to increase in speed >35 mph for NOx >55 mph for CO Less delay and increased average speed Figure 6. Interrelationship between the change in vehicle mix and emissions

8 90 Urban Transport and the Environment for the 21st Century Discussion Simulation results represent the contribution of traffic emissions to the concentration of a particular pollutant in the air. They do not account for other sources in the area. For instance, simulated particulate matter concentrations were far less than field measurements indicating that the transport sector is not the main source for particulate in the air which is not surprising especially that gasoline is the main fuel used in Lebanon and diesel usage is restricted to heavy vehicles. The elevated particulate concentrations can be attributed to construction activities associated with the large effort of post war rehabilitation. In contrast, the simulated concentrations of NO* were within the same order of magnitude as those measured in the field indicating that the transport sector is the major source (El-Fadel et al.\ Strategies for Air uality Management Similar to many developing countries, the transport sector is a major contributor to air pollution in Lebanese urban areas. Pollutant concentrations in the air are expected to increase in the future due to increase in travel demand, the vehicle fleet and corresponding emissions. Hence, there is a need for long term strategies for air quality management. In this regard, policies for emission reduction are proposed below (Staudte et a/7): Minimize dust emissions during construction activities by adopting measures such as proper site enclosure; on-site mixing and unloading operations; adequate maintenance and repair of construction machinery; minimal traffic speed on-site; and proper water spraying when necessary. Adopt a fuel improvement strategy that focuses on 1) phase out of leaded fuel or encouraging the usage of unleaded fuel through an emission based taxation policy; 2) reduction of sulfur content in diesel fuel to less than 0.05 percent; and 3) the usage of alternative fuels especially compressed natural gas which has a promising cost-emission trade off and constitutes an efficient substitute for diesel-fueled buses. Modify specifications for leaded gasoline to reduce the allowable amount of lead to no more than 0.15 g/liter. Eliminate taxes on catalytic converters and enforce its presence on new cars. Adopt a proper vehicle maintenance and inspection program. At present, vehicle inspection is required at registration time, there are no instruments to conduct emission tests. Certificates are issued on a regular basis in exchange for cash payments without subjecting the vehicle to an actual inspection. Provide incentives for emissions reduction including a tax increase on leaded gasoline and diesel and elimination of taxes on unleaded fuel. Develop air quality standards that rely on scientific procedures. Improve the public transport system especially inside the GBA. Restrict park space in the City.

9 Urban Transport and the Environment for the 21st Century 91 Conclusion Air pollution constitutes a major environmental concern particularly in urban areas which are characterized with heavy traffic and high pollutant emissions from transport activities. Congested intersections are frequent occurrence in these urban areas. Grade separations are often proposed as the solution to alleviate the congestion problem. An air quality impact assessment at a typical intersection where a grade separation is proposed was presented in this paper. For this purpose, computer simulations were conducted to define concentrations in the air of selected pollutants with and without the grade seperation as well as with changing the fleet vehicle mix through the introduction of a mass transit system to manage traffic congestion. The simulations showed that a grade separation and the change in fleet vehicle mix reduced exposure to CO concentrations in the air at ground level. Exposure to NO* was also reduced but not as significantly. Acknowledgements The authors wish to express their gratitude to TEAM International for providing the layout of the intersection and data on traffic counts. Special thanks are extended to Mr. E. Bou zeid for his assistance in the early stages of this project. References 1. ARE (Air Resources Board), Methodology for Estimating Emissions from on-road Motor Vehicles (6 volumes), Technical Support Division, Mobile Source Emission Inventory Branch, California EPA, AUB (American University of Beirut), Weather Data Summary, Department of Mechanical Engineering, American University of Beirut, Beirut, Lebanon, El-Fadel M. & Bou Zeid E., Greenhouse gas emissions from the transportation sector in developing countries: the case of Lebanon, Journal of Transportation Research, Part D, 4, 4, , E-Fadel M., Abou Najm M. & Sbayti H., Air uality Modeling at Grade Separation Intersections in Greater Beirut Area, American University of Beirut, Department of Civil and Environmental Engineering, Faiz, A., Weaver, C.S. & Walsh, M. P., Air Pollution from Motor Vehicles: Standards and Technologies for Controlling Emissions, World Bank, Washington D.C., Shaaban F. and Ayoub G. Database of Air and Noise Pollution. National Council for Scientific Research, Beirut, Lebanon, 1996.

10 92 Urban Transport and the Environment for the 21st Century 1. Staudte, M, Rau, M. & El-Fadel, M., Urban Air uality Monitoring Program for the Greater Beirut Area, Transtec-Fitchner Consortium, Ministry of Environment, Beirut, Lebanon, TEAM International Greater Beirut Transportation Plan, Data Collection, Report No.4. Council for Development and Reconstruction, Beirut, Lebanon, TEAM International Greater Beirut Transportation Plan, Household Survey Results, Report No.9. Council for Development & Reconstruction, Beirut, Lebanon, Vicente J. Garza & Peter Graney Transportation Project-Level Carbon Monoxide Protocol, Institute of Transportation Studies, University of California-Davis, Jan