The Relationship between On-Road FFCO₂ Emissions and Socio-Economic/Urban Form Factors for Global Cities: Significance, Robustness and Implications

Round 1

Reviewer 1 Report

Dear Authors,

Dear Editors,

In this comment, after a global synthesis of the article, I will leave some suggestions for improving the article, which presents a good quality in general. The commented manuscript is attached to this revision.

This manuscript addresses a topic widely discussed in several countries, by academic and non-academic organizations and at several levels in the context of transport and urban planning for sustainable development. It focuses on an attempt to demonstrate the relationship between the carbon emission from road transport and some socioeconomic and urban factors.

The article presents an adequate structure to the journal's norms.

The introduction presents a good theoretical support, valuing the importance of the theme and its application at the level of urban policies. Authors had a good research work to identify  several studies with quantitative approaches to the relationship between factors, presenting summary tables of the studies and the elasticity values estimated. Study limitations are also explained, limitations that are intended to be minimized with this study.

In Methods and data section, study area is well explained, based on data availability. The explanation of data sources and methodology is clear. Methods are well described, based on bibliographic references, and data quality is checked and justified.

The results are clearly described and confronted with other studies. Tables are clear (with space to improve) and the authors presented some squemes in order to facilitate the data reading, since in the text, the description sometimes becomes quite heavy/technical.

In the discussion of results, some national realities are explained, in order to confront with the produced data by the authors. However, these data refers to countries, and the data produced are related to "global cities", which we have very different profiles. The relationship between the factors is discussed and the main factors influencing the production of FFCO2 are identified. In the discussion, it is then mentioned what factors should be taken into special consideration in the political action to mitigate CO2 emissions, which is in line with the requests explained below in the Introduction section. Again, the limitations of the study and the limitations on other studies that it aims to minimize are clearly identified.

Finally, conclusions are clear, summarizing the main conclusions and identifying the main limitations of the work. A brief reference to the importance of this study for science is presented, but its importance is not underlined to support decision making in urban planning or transport policies. A further line of investigation is also identified.

The article presents a vast bibliographic reference. However, there are some possible references in Sustainability journal that could be considered too (eg. article "Changing Urban Form and Transport CO2 Emissions: An Empirical Analysis of Beijing, China" (https://0-www-mdpi-com.brum.beds.ac.uk/2071- 1050/6/7/4558). Given the importance of the authors, some relevant references may be included (see, for example, some references of Banister, Black or Stead), about the discussion about transport and land use in a sustainable/unsustainable approach.

Due to the consistency of the article, its capacity for replication, the usefulness of the results and its application in science and in urban planning and transport policies, I consider that the article has quality and is academically sound to publish in Sustainability.

With more detail, it is suggested to the autors, to consider:

In Introduction section

- Including a paragraph with the structure of the article (perhaps after split the introduction from the literature review);

- I suggest, in a possible reformulation, to add a small reference to a theoretical/urban policy approach that justify the importance of the studied theme for “the world”, focusing, for instance, the relevance for Sustainable Development Goals, namely Goal 11. Make cities and human settlements inclusive, safe, resilient and sustainable (https://sustainabledevelopment.un.org/post2015/transformingourworld) (supported in references as United Nations, Banister, Black);

- In order to make it consistent with the Discussion section, the relevance to mitigation of FFCO2 in policies should be clearly identified. Why is GHG emission mitigation so relevant in urban policies? [This point is linked with Sustainable Development Goals / Healthy Movements, etc.]

In Methods and data section:

- Table A-5 should be included in the main text (if it does not compromise the size of the article) so that the reader can better understand the global set of cities studied, that despite being considered "global cities", present very different characteristics (see the maximums and minimums of each variable).

- the authors should consider to present a map with the location of all studied cities as socioeconomics / urban form characteristics are different from continent to continent;

In Results:

- The authors could have some more attention to the tables formatting (tables 6, 7, 8) to facilitate the reading;

In Discussion section:

- Along with advancing the technological efficiency of vehicles, could the authors consider including a small reference about the role of electric cars in this theme? Is this contributing already to reduce or control the increase of fuel consumption and CO2 production?

In Conclusions section:

- The authors highlighted the relevance foi policy making during the text. It is a revelant subjet to include in the conclusions and to justify the "implications" concept present in the main title. How this study could be used in policy making? As a diagnosis? As a monitoring system?

- Is this method replicable in other contexts / realities (cities within a country, cities with some specific dimension) as the data are fully available?

- Sentence about further studies should be individualized in the last paragraph.

Bibliography and cited references

- Please, check some inconsistencies between cited authors and the final references (see the attached file);

- The bibliography should be homogeneized as the references do not present a unique pattern.

Other minor comments

- There are some typos;

- the authors should consider to include "global cities" as keywords;

- table 2 – line 1 – include the country, as in the following lines

- Please, be aware of use acronyms without present it in extense (ex. page 2)

Congratulations and all the best for you.

Comments for author File: Comments.pdf

Reviewer 2 Report

The paper advances the understanding of the driving factors of on-road fossil-fuel CO₂  (FFCO2) emission using data from multiple cities. It uses STIRPAT regressions to evaluate the predicting power of fuel economy, vehicle ownership, population density and road density have significant relationships with on-road FFCO2 emissions.

The article is interesting, well-structured and well written. The analysis appears sound and the results are related to the data and analysis. The results are providing a new look at the problem in a way not previously done in the literature which is appreciated and useful. The authors present relevant literature and mostly summarize it well, see specific comment for details. However, an unacceptable number of mistakes appear in the reference list. 29 items are listed in the reference list that do not appear to be cited in the text, that appears very unusual to this reviewer. Furthermore 16 references used in the text are not included in the reference list. This is a major issue. The details of these missing items are provided below. The literature review is included as part of the introduction, however, it appears strong enough to stand on its own. The annex 1 cited in the text was also missing for the review and is necessary for the reviewer to form a complete opinion of the work. Some figures would gain from further comments by the authors. Finally, the version of the discussion included in the paper for review feels like a draft and the reviewer wonders if this is really the final version intended to publish. We come to this sad conclusion about the discussion as it contains “references” without any references at multiple locations and it appears rushed.

Major issues

1. The following 29 items are listed in the reference list but are not cited in the text. This reviewer strongly encourages the authors to use a reference management system like Zotero to prevent these issues
   1. Bento, A., Cropper, M., Mobarak, A., Vinha, K., (2003), The Impact of Urban Spatial Structure on Travel Demand in the United States, Worldbank Policy Research Working Paper Series, 3007
   2. Berube, Alan, Alec Friefhoff, Carey Nadeau, Philipp Rode, Antoine Paccoud, Jens Kandt, Tobias Just, and Reto Schemm-Gregory, (2010), Global metro monitor: the path to economic recovery: a preliminary overview of 150 global metropolitan economies in the wake of the great recession. Web source: http://eprints.lse.ac.uk/47898/1/Berube_Global_metro_monitor_2010.pdf
   3. Breheny, M. (1995). The compact city and transport energy consumption. Transactions of the institute of British Geographers, 81-101.
   4. Browne, W. M., (2000), Cross-validation methods, Journal of Mathematical Psychology, 44, 108-132
   5. Cuenot, F. and Fulton, L., (2011), International comparison of light-duty vehicle fuel economy and related characteristics, Global Fuel Economy Initiative, International Energy Agency
      
      
   6. Dare, P.M., (2005), Shadow analysis in high-resolution satellite imagery of urban areas, Photogrammetric Engineering and Remote Sensing, 71, pp. 169–177
   7. Doane, David P., and Lori E. Seward., (2011), Measuring Skewness: A Forgotten Statistic? Journal of Statistics Education 19.2, 1-18.
   8. Eurostat, (2012), Quality Assurance Framework of the European Statistical System, European Statistical System
   9. Forghani, M.; Delavar, M.R., (2014), A Quality Study of the OpenStreetMap Dataset for Tehran. ISPRS Int. J. Geo-Inf., 3, 750-763.
   10. GADM, (2012), Global Administrative Areas, GADM database of Global Administrative Areas, version 2.0. www.gadm.org.
   11. Google, (n.d.), Google Earth at www.google.com/earth
   12. IPCC 2006, IPCC Guidelines for National Greenhouse Gas Inventories, Prepared by the National Greenhouse Gas Inventories Programme, Eggleston H.S., Buendia L., Miwa K., Ngara T. and Tanabe K. (eds). Published: IGES, Japan
   13. Kennedy, C., Steinberger, J., Gasson, B., Hansen, Y., Hillman, T., Havránek, M., Mendez, G. V. (2010). Methodology for inventorying greenhouse gas emissions from global cities. Energy Policy, 38(9), 4828- 4837.
   14. LandScan, 2011, This product was made utilizing the LandScan (2011)TM High Resolution global Population Data Set copyrighted by UT-Battelle, LLC, operator of Oak Ridge National Laboratory under Contract No. DE-AC05-00OR22725 with the United States Department of Energy. The United States Government has certain rights in this Data Set. Neither UT-BATTELLE, LLC NOR THE UNITED STATES DEPARTMENT OF ENERGY, NOR ANY OF THEIR EMPLOYEES, MAKES ANY WARRANTY, EXPRESS OR IMPLIED, OR ASSUMES ANY LEGAL LIABILITY OR RESPONSIBILITY FOR THE ACCURACY, COMPLETENESS, OR USEFULNESS OF THE DATA SET.
   15. Li, HI-Chun; Chen, Yak-Juan; Wang, Ya-Dong; Lam, William H.K. and Wong, S.C., (2013), Optimal density of radial major roads in a two-dimensional monocentric city with endogenous residential distribution and housing prices, Regional Science and Urban Economics, 43, (6), 927-937
   16. Lo, C. P. (2004), Testing Urban Theories Using Remote Sensing. GIScience & remote sensing, Volume 41, Number 2, pp. 95-115
   17. Massey, Douglas S., and Nancy Denton. 1988. The dimensions of residential segregation. Social Forces 67:281-
   18. 
       Mosier, C., (1951), Problems and designed of cross-validation, Symposium: the need and means of cross-validation.
   19. Noland, R. B., & Lem, L. L. (2002). A review of the evidence for induced travel and changes in transportation and environmental policy in the US and the UK. Transportation Research Part D: Transport and Environment, 7(1), 1-26.
   20. Oliveira, E., Andrade Jr. J., & Makse, H., (2014). Large cities are less green. Scientific Reports, 4, 4235.
   21. Pan, Xian-Zhang, Zhao, Qi-Guo, Chen, Jie, Liang, Yin and Sun, Bo, (2008), Analyzing the Variation of Building Density Using High Spatial Resolution Satellite Images: The Example of Shanghai City, Sensors 2008,8(4), 2541-2550; doi:10.3390/s8042541
   22. Taubenböck, H., Klotz, M., Wurm, M., Schmieder, J., Wagner, B., Wooster, M., ... & Dech, S. (2013). Delineation of central business districts in mega city regions using remotely sensed data. Remote sensing of Environment, 136, 386-401.
   23. USBLS, (n.d.), Local Area Unemployment Statistics, United States Bureau of labor statistics
       United States Census Bureau (USCB), (n.d.), Population and Housing Unit Estimates
   24. Van Der Waals, J. (2000). The compact city and the environment: A review. Tijdschrift voor economische en sociale geografie, 91(2), 111-121.
   25. Wheaton, W. C. (2004). Commuting, congestion, and employment dispersal in cities with mixed land use. Journal of Urban Economics, 55, 417-438.
   26. Wu, C, Murray, A., (2003), Estimating impervious surface distribution by spectral mixture analysis, Remote Sensing of Environment, Volume 84, Issue 4, 10 April 2003, Pages 493-505
   27. Yi, Y., Ma, S., Guan, W., & Li, K. (2017). An empirical study on the relationship between urban spatial form and CO2 in Chinese cities. Sustainability, 9(4), 672.
   28. York, R., Rosa, E. A., & Dietz, T. (2003). STIRPAT, IPAT and ImPACT: analytic tools for unpacking the driving forces of environmental impacts. Ecological economics, 46(3), 351-365.
   29. Yu, Wenhao, Ai, Tinghua, Shao, Shiwei, (2015), The analysis and delimitation of Central Business District using network kernel density estimation, Journal of Transport Geography, Volume 45, May, Pages 32–47
2. The following 16 references cited in the text are not included in the reference list:
   1. Line 48: Shrestha (2009)
   2. Line 64: Eltony and Al-Mutairi (1995)
   3. Line 78: (Wheaton, 1998)
   4. Table 2: Noland and Cowart (2000)
   5. Line 117, York 2003, probably York et al. 2003, but uncertain
   6. Table 3: (ORNL, 2011)
   7. Table 3: (Berube et. al., 2015)
   8. Table 3: (Cuenot and Körner, 2011)
   9. Table 3: (World Road Statistics, 2014)
   10. Line 209: (Bento et. al., 2005)
   11. Line 268: (Bento et. al., 2005)
   12. Line 276: Ewing and Cervero, 2010
   13. Line 303: Lu and White 2010)
   14. Line 339: (Small and Van Dender, 2006)
   15. Line 351: et. al. (2013),
   16. Line 404: (Espey, 1996)
3. Annex 1 is missing and is required for peer review purposes
4. On line 245 Figure 1 is described much too succinctly. The authors need to actually discuss the figure.
5. The discussion appears rushed and unfinished. For example, line 361 and line 363 point to “references” that are not provided. On line 363, “regular” should probably be “regulate” instead. On line 385, “demonstrates an more” should be “demonstrates a more”

Minor issues

6. On line 52, the authors describe the statistically relevant relationships between the emission and the different variable without specifying if this is a reinforcing (positive) relationship or if it is a (weakening) negative relationship, the paper would gain from providing this extra level of detail.
7. A similar issue appears on line 74 where the authors describe a “strong impact” without specifying if it is a positive or negative impact.
8. On line 79 the authors state that “Many case studies also did not observe a significant relationship between increasing urban compactness and decreased transportation energy consumption”.The following paper Munafò, Sébastien. « Forme urbaine et mobilités de loisirs : l’« effet barbecue » sur le grill ». Cybergeo, 16 October 2017. https://0-doi-org.brum.beds.ac.uk/10.4000/cybergeo.28634, albeit in French, describes an empirical quantitative research which shows that there is a relationship. If the authors speak French they might consult that paper.
9. In table 2 the authors provide a sample of studies calculating FFCO2 and urban form, they might want to also include the following paper: Kinigadner, Julia, Benjamin Büttner, et Gebhard Wulfhorst. « Beer versus Bits: CO 2 -Based Accessibility Analysis of Firms’ Location Choices and Implications for Low Carbon Workplace Development ». Applied Mobilities 4, nᵒ 2 (4 May 2019): 200‑ https://0-doi-org.brum.beds.ac.uk/10.1080/23800127.2019.1572053.

Author Response

Thank you for your review. Here are the revisions that we made according to your comments:

1. The following 29 items are listed in the reference list but are not cited in the text. This reviewer strongly encourages the authors to use a reference management system like Zotero to prevent these issues

2. The following 16 references cited in the text are not included in the reference list:

The authors revised the reference and checked throughout the document to make sure there are no reference not cited and no cited references not included in text. All references were added the number order to facilitate easier search.

3. Annex 1 is missing and is required for peer review purposes

The authors are unclear about what is Annex 1 referring to.

4. On line 245 Figure 1 is described much too succinctly. The authors need to actually discuss the figure.

The corresponding discussion about figure 1 has been added into the revised document. 

Figure 1 illustrates the corresponding correlation result from single regression and multiple regression for these predictors. Circles in figure 1 represent the variations of dependent variable (DV) and independent variables (IV). The top row of figure 1 illustrated the relationships between the DV and IV in a single regression model (while ignoring the impacts of other IVs); the bottom row illustrated the relationships between the same combination of DV and IV in the multiple regression model (while controlling the rest of the IVs).

5. The discussion appears rushed and unfinished. For example, line 361 and line 363 point to “references” that are not provided. On line 363, “regular” should probably be “regulate” instead. On line 385, “demonstrates an more” should be “demonstrates a more”

Corresponding places were fixed in the revised document.

6. On line 52, the authors describe the statistically relevant relationships between the emission and the different variable without specifying if this is a reinforcing (positive) relationship or if it is a (weakening) negative relationship, the paper would gain from providing this extra level of detail.

A more detailed description was added into the revised document.

Barla, et. al. [1] utilized survey data to explore the impacts of individual/household socio-economic characteristics on transportation greenhouse gas emissions. They found relationships (statistically significant at 1% level) between the transportation GHG emissions and population age (emissions start to decline after age 50), gender (females produce 25% less emissions than males), income (high income links to high emissions) and neighborhood (10% more denser neighbourhood would reduce 1.2% emissions on average).

7. A similar issue appears on line 74 where the authors describe a “strong impact” without specifying if it is a positive or negative impact.

A more detailed description was added into the revised document.

Wang, et.al. [66] analyzed urbanization and on-road FFCO₂ emissions data in Beijing from 2000 to 2009 and found that decentralization of Beijing had a strong aggravating impact on on-road FFCO₂ emission due to the increasing commute distances and shifting travel mode to private cars instead of public transit.

8. On line 79 the authors state that “Many case studies also did not observe a significant relationship between increasing urban compactness and decreased transportation energy consumption”.The following paper Munafò, Sébastien. « Forme urbaine et mobilités de loisirs : l’« effet barbecue » sur le grill ». Cybergeo, 16 October 2017. https://0-doi-org.brum.beds.ac.uk/10.4000/cybergeo.28634, albeit in French, describes an empirical quantitative research which shows that there is a relationship. If the authors speak French they might consult that paper.

Sorry French is not the authors' native language but thanks for pointing out the literature.

9. In table 2 the authors provide a sample of studies calculating FFCO2 and urban form, they might want to also include the following paper: Kinigadner, Julia, Benjamin Büttner, et Gebhard Wulfhorst. « Beer versus Bits: CO 2 -Based Accessibility Analysis of Firms’ Location Choices and Implications for Low Carbon Workplace Development ». Applied Mobilities 4, nᵒ 2 (4 May 2019): 200‑ https://0-doi-org.brum.beds.ac.uk/10.1080/23800127.2019.1572053.

The authors had difficulty searching for this paper. The DOI link requires payment and this paper is not included in the educational database.

The authors searched and found another paper by the same author that can be searched through the paid educational database.

Julia Kinigadner, Benjamin Büttner, Gebhard Wulfhorst,
Accessibility planning based on CO2 emissions – implications for employment development within the Munich Metropolitan Region,
Transportation Research Procedia,
Volume 41,
2019,
Pages 593-595,
ISSN 2352-1465,
https://0-doi-org.brum.beds.ac.uk/10.1016/j.trpro.2019.09.106.

This paper seems related to the reviewer's suggestion according to the abstract. However it seems like a conference paper without details in methods and data. If the reviewer would provide the full text of the recommended paper, the authors would be gladly to add it in the revision.

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear Author, 

You have done good work, Please have a look at the following comments and respond accordingly: 

Line 55-60- too long sentence please break it. Also explain the salient features of the Table-1 such as Eltony and Al Mutairi (1995) row. Check row Lu, et. al. (2007) and make it more clear, if you could.

Line 65-Format Table 1, also its  title is too long.

Table 2- Noland and Cowart, (2000) -last column "US states" do you mean nation-wide or rest of the states of America?

Line 116- “When one variable changes while others are held constant, the controlled variables will still influence the environmental impact (York, 2003)”. Check if this sentence  could be rephrased for more clarity. 

Line 146- Please write APPENDIX number on all Appendices at the ned in Bold letters. 

Line 187- “misspecification” can you please use any other simple term or explain it further.

Line 199- check -with mean=1 and standard deviation=σ

Line 203-  “was shown in table 8.” Change it to  “Is shown in Table 8”.

Line 222-224- Could the title of Table 4 be short?

Table-4 needs formatting, you may change the font sizes.

Line 300- Please Use capital “T” in bracket (Table 6)

Line 3.5- MPG is less sensitive) remove close bracket or show where open bracket starts.

Line 310-In bracket (Table 7), “ T” should be capital

Line 316- Sentence start with 100%, please rephrase the sentence

Line 321-In the bracket (Table 8) "T" should be capital

Line 337-338- check the sentence, possibly, rephrase it in order to  compare with the Australian data

Line 384: “an more” change it to “a more”

Line 404-   You may avoid reference "(Eltony, 1993; Espey, 1996)" (in the conclusion) and make it a generic statement.

Line 422-423- double space needed.

Author Response

Thank you for your review. Here are a point by point response to your comments.

Line 55-60- too long sentence please break it. Also explain the salient features of the Table-1 such as Eltony and Al Mutairi (1995) row. Check row Lu, et. al. (2007) and make it more clear, if you could.

The long sentense was broken down in two.

Certain socio-economic factors were identified in previous studies to have a significant relationship to transportation energy use. Their resulting elasticity values (the proportional change of one variable in response to the proportional change of another variable) exhibited a wide range in the different locations, mix of variables considered, and different interpretations of the key variables (Table 1).

The point of the table is to list the wide range of different elasticities from previous research, thus it is merely an illustrative table rather than a comprehensive review.

Line 65-Format Table 1, also its  title is too long.

Table title revised to:

Table 1. Elasticities between socio-economic factors and transportation demand reported in previous research

Table 2- Noland and Cowart, (2000) -last column "US states" do you mean nation-wide or rest of the states of America?

The authors reviewed it again and revised the corresponding column to "United Kingdom and United States"

Line 116- “When one variable changes while others are held constant, the controlled variables will still influence the environmental impact (York, 2003)”. Check if this sentence  could be rephrased for more clarity. 

Yes this sentence is rather confusing. It was deleted to avoid confusion.

Line 146- Please write APPENDIX number on all Appendices at the ned in Bold letters. 

The authors were unclear about this comment. What exact appendix number were referred here?

Line 187- “misspecification” can you please use any other simple term or explain it further.

"misspecification" is replaced by "improper specifications"

Line 199- check -with mean=1 and standard deviation=σ

The artifical errors with mean=1 and deviation=σ (σ varies from 0.05 to 0.5) were added to test the robustness. The description here is correct.

Line 203-  “was shown in table 8.” Change it to  “Is shown in Table 8”.

correction is made in the revised document

Line 222-224- Could the title of Table 4 be short?

title of table 4 is replaced with

Table 4. Results from single-variable linear regression models.

(For each pairwise regression, the slope coefficient, the R² (in parentheses) and the p-values (in brackets) are provided. Statistically significant (p£0.05) are in red; insignificant values are in blue.)

Table-4 needs formatting, you may change the font sizes.

font size changed in revised document

Line 300- Please Use capital “T” in bracket (Table 6)

correction is made in the revised document

Line 3.5- MPG is less sensitive) remove close bracket or show where open bracket starts.

bracket is removed in the revised document

Line 310-In bracket (Table 7), “ T” should be capital

correction is made in the revised document

Line 316- Sentence start with 100%, please rephrase the sentence

100% is replaced with "All"

Line 321-In the bracket (Table 8) "T" should be capital

correction is made in the revised document

Line 337-338- check the sentence, possibly, rephrase it in order to  compare with the Australian data

Sentence is rewritten as:

In Australia, the Survey of Motor Vehicle Usage (SMVU) conducted by the Australian Bureau of Statistics indicated that fuel economy (12 litres per 100 km) has not changed much between 1976 and 2018 [60].

Line 384: “an more” change it to “a more”

correction is made in the revised document

Line 404-   You may avoid reference "(Eltony, 1993; Espey, 1996)" (in the conclusion) and make it a generic statement.

sentence is replaced with

For example, the impacts of GDP or income on fuel consumption are mainly reflected through the variation of vehicle ownership and distance travelled [16, 19]. These effects could take years to become significant.

Line 422-423- double space needed.

correction is made in the revised document

Author Response File: Author Response.pdf