Integrated Approach for the Assessment of Strategies for the Decarbonization of Urban Traffic

Round 1

Reviewer 1 Report

This paper proposed an integrated approach to evaluate various decarbonization strategies across all traffic segments through vehicle design, agent-based transport simulation, operational cost analysis and life cycle assessment.

This topic is an active area, and this paper gives a solid literature review of sustainable transport system with new decarbonization strategies including battery electric vehicle (BEV), electric and autonomous fleets (EAF) and Hydrogen Fuel cell vehicles (FCEV).

The specific comments are as below,

1. The full name of the abbreviation ‘ICEV’ should be given as ‘internal combustion engine vehicle’ when it is first used.
2. Line 597 has the duplicated sentence “The values are calculated per energy unit used.” Please delete one.
3. What are the roles of ‘Social Sustainability in Automation Technologies’ and ‘Total Cost of Ownership’ in the proposed approach and zeroCut toolbox?
4. Is it possible to demonstrate the result of each step in Section 4?
5. I am a little confused about how greenhouse gas emissions are calculated in Section 5. Could you make more explanation?

Author Response

Your Review:

This paper proposed an integrated approach to evaluate various decarbonization strategies across all traffic segments through vehicle design, agent-based transport simulation, operational cost analysis and life cycle assessment.

This topic is an active area, and this paper gives a solid literature review of sustainable transport system with new decarbonization strategies including battery electric vehicle (BEV), electric and autonomous fleets (EAF) and Hydrogen Fuel cell vehicles (FCEV).

The specific comments are as below,

1. The full name of the abbreviation ‘ICEV’ should be given as ‘internal combustion engine vehicle’ when it is first used.
2. Line 597 has the duplicated sentence “The values are calculated per energy unit used.” Please delete one.
3. What are the roles of ‘Social Sustainability in Automation Technologies’ and ‘Total Cost of Ownership’ in the proposed approach and zeroCut toolbox?
4. Is it possible to demonstrate the result of each step in Section 4?
5. I am a little confused about how greenhouse gas emissions are calculated in Section 5. Could you make more explanation?

 

Dear Reviewer,

Thank you very much for reading and reviewing our paper. We have analyzed your feedback carefully and adapted our paper wherever this was possible. We believe our paper has benefited greatly from your review and the resulting improvements.

In the following, we will answer to each of your specific comments and indicate what changes have been made:

1. Thank you for pointing out this flaw. The full name has been included where the abbreviation was first mentioned (Line 591).
2. We apologize for this mistake and have of course resolved this issue.
3. It is important that you have noticed that the description of the meaning of these tools has not been sufficient so far. In the introduction to Section 4, we now included a detailed description of the background to our methods for quantifying the three dimensions of sustainability (Lines 402-413).
4. Since we are trying to give a broad overview of the entire project, we find it hard to go into detail with every considered segment and scenario. However, we have added additional results to Section 5. Now we have for each segment the key outcomes of the simulation, the charging layout, if needed, and the results of our sustainability assessment. For more detailed results and the complete description of our method we believe it is better to refer to our specific papers which provide more details for the interested reader. We cited these publications along with the respective results. (Lines 794-795 and 830-841; Figure 6 and Figure 8)
5. In Section 5.1 we have now included that full life cycle emissions are calculated (Lines 723-724). In the rest of Section 5, we calculate well-to-wheel emissions (Lines 806 and 849). Both are explained in Section 4.5.

We hope that our changes and explanations will resolve your concerns.

Best Regards

The Authors

Reviewer 2 Report

The authors present a very complex and elaborated tool to perform a detailed analysis of the impact of several transport segments, with a focus on the city of Berlin. I think the work is outstanding, although the quality of the presentation could be further improved to reflect the quality of the method the authors are proposing.

My main recommendations are the following:

The description of the methodology is very long, with a lot of qualitative details and descriptions. However, I think in some cases it could be useful to provide also some quantitative information. For example, when considering private cars, a rising concern in the EU (and in Germany) is the increasing trend of large-size cars and SUVs, which is in turn increasing the average emissions of new cars. Have you considered this potential effect in your model? Can you discuss the potential effects on your results? Some figures on the average features of the private cars (e.g. average size, engine, weight, year/age, emissions, etc.) may be useful to compare your results with other studies.

While it is clear that the description of the methodology is very detailed, I think that the results are rather limited. I acknowledge that you are presented preliminary results and the work is still in progress, but my feeling is that the paper is very unbalanced. Moreover, while it is good for the readers to have the reference to other works to find additional results, I think that you should provide at least some additional information as supplementary material. And in general, the results that you are providing could be better presented, such as by comparing them between each other, or putting them in context, i.e. comparing them using the framework presented in figure 8.

The abstract and the introduction is strongly highlighting the role of transport in environmental impacts, which I think is a very important focus. In addition to climate effects, local pollution is a very important topic for cities. While you correctly highlight the importance of local emissions in the introduction, in your model it seems that they have not been considered. You define the impact on “total particulate matter” in some of your LCA results (although it is not clear how they are quantified – and urban emissions are very different than emissions in coal plants for electricity), but no mention of NOX and other pollutants is given. I think this is a limitation that should be clearly stated, because in the abstract you are mentioning several times “environmental impacts”, which could be misleading. I know that LCA studies are usually considering specific impact categories, but since you are focusing on transport this issue should be clearly addressed or at least discussed. Moreover, with an agent-based model there would be the potential of providing additional useful information on the distribution of the local pollution, which could be a future evolution of your research.

 

Additional minor aspects to be addressed:

There are some typos in the manuscript, please double-check the English (e.g. 319 “This results”. Line 597: a sentence is repeated, etc.).

Lines 332-336: In Germany also hydrogen trains are a popular alternative for non-electrified lines. Have you evaluated this opportunity?

Lines 339-344: An additional issue in many cities is the limited range of electric buses, which is often lower than the required daily mileage. You discuss it at line 353, but maybe it would be better to discuss it above.

Section 5.1.1 – Some qualitative key results are presented, without any explicit reference in the paper. I think that at least a table in appendix would be required, to justify the claims of the authors.

 

 

Author Response

Your Review:

The authors present a very complex and elaborated tool to perform a detailed analysis of the impact of several transport segments, with a focus on the city of Berlin. I think the work is outstanding, although the quality of the presentation could be further improved to reflect the quality of the method the authors are proposing.

My main recommendations are the following:

1. The description of the methodology is very long, with a lot of qualitative details and descriptions. However, I think in some cases it could be useful to provide also some quantitative information. For example, when considering private cars, a rising concern in the EU (and in Germany) is the increasing trend of large-size cars and SUVs, which is in turn increasing the average emissions of new cars. Have you considered this potential effect in your model? Can you discuss the potential effects on your results? Some figures on the average features of the private cars (e.g. average size, engine, weight, year/age, emissions, etc.) may be useful to compare your results with other studies.
2. While it is clear that the description of the methodology is very detailed, I think that the results are rather limited. I acknowledge that you are presented preliminary results and the work is still in progress, but my feeling is that the paper is very unbalanced. Moreover, while it is good for the readers to have the reference to other works to find additional results, I think that you should provide at least some additional information as supplementary material. And in general, the results that you are providing could be better presented, such as by comparing them between each other, or putting them in context, i.e. comparing them using the framework presented in figure 8.
3. The abstract and the introduction is strongly highlighting the role of transport in environmental impacts, which I think is a very important focus. In addition to climate effects, local pollution is a very important topic for cities. While you correctly highlight the importance of local emissions in the introduction, in your model it seems that they have not been considered. You define the impact on “total particulate matter” in some of your LCA results (although it is not clear how they are quantified – and urban emissions are very different than emissions in coal plants for electricity), but no mention of NOX and other pollutants is given. I think this is a limitation that should be clearly stated, because in the abstract you are mentioning several times “environmental impacts”, which could be misleading. I know that LCA studies are usually considering specific impact categories, but since you are focusing on transport this issue should be clearly addressed or at least discussed. Moreover, with an agent-based model there would be the potential of providing additional useful information on the distribution of the local pollution, which could be a future evolution of your research.

 

4. There are some typos in the manuscript, please double-check the English (e.g. 319 “This results”. Line 597: a sentence is repeated, etc.).
5. Lines 332-336: In Germany also hydrogen trains are a popular alternative for non-electrified lines. Have you evaluated this opportunity?
6. Lines 339-344: An additional issue in many cities is the limited range of electric buses, which is often lower than the required daily mileage. You discuss it at line 353, but maybe it would be better to discuss it above.
7. Section 5.1.1 – Some qualitative key results are presented, without any explicit reference in the paper. I think that at least a table in appendix would be required, to justify the claims of the authors.

 

Dear Reviewer,

Thank you very much for reading and reviewing our paper. We highly appreciate the time and effort you put into this extensive and in-depth review. We have analyzed your feedback carefully and adapted our paper wherever this was possible. We believe our paper has benefited greatly from your review and the resulting improvements.

We have taken the liberty of numbering your comments so that we can address them point by point in the following:

1. Thank you for mentioning the increasing share of SUVs in the passenger car segment. We have included this trend in another recent publication (Scharf et al. 2020). However, in this publication we do not consider a specific future state (e.g. the year 2030) but build a theoretical scenario in which today's passenger car segment with the current vehicle distribution is converted to 100% battery electric. The temporal transient towards this state is outside the scope of this work. Of course, this approach is debatable. However, we believe that it provides the best possible comparability between the status quo and the strategies we analyze. We have therefore deliberately decided to exclude developments in the passenger car segment from the analysis. We have included our reasoning in the discussion (Lines 918-923) in order to clarify this issue for subsequent readers. Also we provided additional information on the vehicle distribution in Table 2 and the vehicle features in Table 1 (Lines 725-727).
2. Thank you for pointing this out. For us, it was a difficult balancing act of how many results we could put into this clearly method-focused paper to make it understandable but not overloaded. Thanks to your comments, we have now been able to adjust this ratio and have added some additional results. Now we have for each segment the key outcomes of the simulation, the charging layout, if needed, and the results of our sustainability assessment. For more detailed results and the complete description of our method we believe it is better to refer to our specific papers which provide more details for the interested reader. We cited these publications along with the respective results. (Lines 794-795 and 830-841; Figure 6 and Figure 8). As you have suggested, we have added a short comparison of the most important results in the discussion. (Lines 864-870)
3. We have mentioned the direct (driving) emissions in the introduction because they are, as you have pointed out, a very important factor for urban traffic. But since both BEVs and FCEVs do not cause tailpipe emissions like NOX, CO and HC, the resulting reduction of these emissions is rather trivial. Of course, depending on the electricity source, these emissions might still occur, but in different locations. Therefore, we include them in our LCA. You are absolutely right that the results of our traffic simulation can make a major contribution to predicting local concentrations of pollutants. However, other polluters such as industry or household heating systems also play a role. Therefore, local pollutant concentrations are unfortunately well outside our scope. We have added a paragraph about this matter in the discussion section. (Lines 888-893)
4. Thank you for letting us know. We have corrected the mentioned mistakes.
5. You are absolutely right. Hydrogen trains are also a possible option and they are tested for example by Siemens. However, in this project we do not consider trains at all. Hydrogen trains for urban transport seem not to be a meaningful solution, as inner-city rail traffic is already completely electrified in our use case. And the battery electric train is another research project we are involved in so we used it as an example. 
6. Since our method performs a replanning of the tours (which considers the possible range of the busses under all possible conditions), this issue is taken care of. For depot charging this results in the indicated increase in necessary vehicles. Also we consider opportunity charging which eliminates the range issue completely (See Section 4.3).
7. We added another figure to Section 5.1.1 (Figure 6) that shows the results for the other mentioned impact categories. Further information like the used impact assessment methods and the results per lifetime mileage can be found in Syré et al. (2020). 

We hope that our changes and explanations will resolve your concerns.

Best Regards

The Authors

 

Round 2

Reviewer 1 Report

Please make a thorough check about the writting since there are still some typos in the manuscript.

Author Response

Thank you for this advice.

We did another round of proof reading.

Reviewer 2 Report

The authors have addressed my recommendations.

Author Response

Thank you for this positive feedback.