Nuevo escenario: Espacio Europeo de Educación Superior

As noted before, the spacing between adjacent roundabouts along the corridor has a higher impact on vehicular emissions than entry deflection angle. Thus, the CO2 and CO emissions

amounts by segment are plotted against the spacing and the entry deflection angle, as depicted in Figure 3.9a-d. For values lower than 150 m for the spacing, vehicles generate the highest values of CO2 and CO emissions per unit distance (Figure 3.9a-b). After, the values tend to be

relatively constant between 150 and 350 m. The R2 _{values of CO}

2 and CO emissions for spacing

are 0.53 and 0.41, respectively. This means that the model for CO2 better explains the variability

in the data than the model for CO. This can be explained by sharper acceleration-deceleration rates within adjacent roundabouts which have more impact on carbon monoxide emissions. In contrast, the R2 _{values for the entry deflection are lower than 0.20 for both variables (Figure} 3.9c-d). These findings are particularly relevant since they do not take into account site-specific

conditions of the roundabout corridors. Also, they are in line with the results presented in previous sections.

a) b)

c) d)

Figure 3.9 Emissions per unit distance for corridor design features: a) CO2 versus spacing; b)

CO versus spacing; c) CO2 versus entry deflection angle; d) CO versus entry deflection angle.

3.5. Conclusions

This research introduced a methodology to measure and quantify the emissions of the different segments of functionally interdepend roundabouts on arterials. The segments considered were the circulating area of each roundabout, downstream, mid-block and upstream between adjacent roundabouts. The paper also identified the emission hotspots along the corridor, either in absolute terms as per unit distance. To accomplish the objectives posed, four corridors with roundabouts exhibiting similar design features (posted speed limit, total corridor length, low

y = 0.0013x2_{- 0.7347x + 265.69} 0 100 200 300 0 100 200 300 400 CO 2 [g/km] Spacing [m] R2_{= 0.53} y = 0.0029x2_{- 1.5999x + 589.63} 0 200 400 600 0 100 200 300 400 CO [mg/km] Spacing [m] R2_{= 0.40} y = 0.0357x2_{- 2.2199x + 202.02} 0 100 200 300 0 15 30 45 60 CO 2 [g/km]

Entry Deflection Angle [º]

R2_{= 0.16} y = -0.0284x2_{+ 3.2436x + 317.28} 0 200 400 600 0 15 30 45 60 CO [mg/km]

Entry Deflection Angle [º]

spacing between adjacent roundabouts and traffic flows), but a different interspacing of roundabouts (two corridors with equally spaced roundabouts and two with unequally spaced roundabouts) were selected. For emissions estimation, a methodology based on vehicle specific power was used.

It was concluded that the emissions distributions along the corridors with equally spaced roundabouts and enough spacing to attain cruise speed over the mid-block was similar for each pair of adjacent roundabouts. In such cases, the downstream sub-segments were identified as the emissions hotspots (overall contribution on total emissions exceeded the 34%) both in absolute terms and per unit distance. Considering the corridors with unequally spaced roundabouts, the CO2 and CO emissions hot spots per unit distance, about 9% higher than the

average corridors values were found at the circulating areas sub-segments. This was particularly true for closely spaced roundabouts (<165 m of spacing) in which vehicles decelerated after the roundabout exit section (at the downstream sub-segment). The evaluation of CO2 and CO

emissions for different values of spacing and deflection angle pointed out to the higher impact of spacing on emissions along corridors (R2 _{> 0.40). In contrast, a slight impact of deflection}

on emissions was noted (R2 _{< 0.20). The findings of the paper suggest that the impact of entry}

deflection angle on acceleration profiles and so that in emissions decreases for low roundabout’s spacing. This aspect is not verified on isolated roundabouts and must be taken into account for design considerations of roundabouts in sequence in a corridor.

The main limitation of this paper is the small sample size of the corridors that were chosen for this analysis. The second limitation is the similar approach and free-flow speeds as well as traffic flows for the four roundabouts studied for this research. It should be also referred that the equality in spacing between adjacent roundabouts does not mean that emission hotspots are attributed to downstream areas. In spite of being a moderate roundabout spacing (ranged from 190 m to 350 m), the selected corridors worked as five (La Jolla) and four (Mealhada) isolated roundabouts. In the hypothetic case of low roundabouts spacing, as was the case of Avon or Chaves corridors (e.g. 100 m), the impacts of downstream and mid-block decrease since vehicles are not able to attain higher speeds. Consequently, the vehicle activity data among downstream, mid-block and upstream is affected.

Therefore, future work is needed, namely: the study of other corridors with different spacing between adjacent roundabouts (extreme low and high interspacing of the roundabouts), roundabouts layouts (e.g. turbo-roundabouts) and the impact of traffic flows and free-flow speed along the corridor on the spatial distribution of emissions.

3.6. Acknowledgments

This work was also partially funded by FEDER – Fundo Europeu de Desenvolvimento Regional Funds through the Operational Program ‘‘Factores de Competitividade – COMPETE’’ and by National Funds through FCT – Fundação para a Ciência e Tecnologia within the project PTDC/SEN-TRA/122114/2010, by the Strategic Project PEst- C/EME/UI0481/2014, FLAD – Luso American Foundation, and Toyota Caetano Portugal, which allowed the use of vehicles. P. Fernandes acknowledges the support of FCT for the Scholarship SFRH/BD/87402/2012. The authors are also grateful to the NCHRP Report 772 for sharing their vehicle activity data at the two US corridor sites.

CHAPTER 3 EMISSION HOTSPOTS IN ROUNDABOUT CORRIDORS

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CHAPTER 3 EMISSION HOTSPOTS IN ROUNDABOUT CORRIDORS

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4. ASSESSMENT OF CORRIDORS WITH TRADITIONAL TYPES OF