Evaluating the emission reduction potential of first underground metro rail in Mumbai, India through a modal shift and energy use perspective
Open accessAbstract
The increasing environmental and health burdens caused by road-based transportation in urban India make it imperative to shift toward sustainable mobility solutions. Metro rail systems offer significant potential for reducing greenhouse gas and air pollutant emissions. This study evaluates the emission reduction potential of the first underground metro rail system in Mumbai, India. The analysis estimates the emissions avoided from reduced on-road vehicle usage and compares them with the emissions generated by metro operations powered by a combination of solar and grid electricity. The study considers five key pollutants, namely carbon dioxide (CO 2 ), carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NO x ), and particulate matter (PM), to assess both climate and local air quality impacts. A mode shift analysis was conducted based on projected ridership of 1.56 million daily passengers and modal share assumptions derived from recent travel behavior studies. Vehicle categories, fuel types, occupancy, and vintage distribution were considered in estimating avoided emissions. Emissions from metro operations were calculated using electricity demand for traction and auxiliary purposes. The results show a net reduction of 155 tonnes of CO 2 per day, along with daily savings of 3871 kg of CO, 2526 kg of HC, 133 kg of NO x , and 82 kg of PM. The greatest emission reductions were achieved by shifting vehicles from two-wheelers (12–48%), auto-rickshaws (19–47%), and taxis (5–34%), owing to their high emission intensity, while buses (9–14%) and cars (4–29%) contributed moderately. A scenario analysis was performed to evaluate the sensitivity of net emission savings to changes in modal shift composition, energy source (solar vs. grid), and ridership levels. Scenario analysis revealed that a greater shift from private vehicles and increased reliance on renewable electricity can further enhance mitigation. The study underscores the importance of renewable energy and strategic modal shift planning to maximize the environmental benefits of the metro rail system.
AI snapshot
Written from the paper’s full text.
TL;DR
This study estimates net emission savings from Mumbai’s first underground metro (Aqua Line/Line 3) by comparing avoided on-road vehicle emissions from modal shift against emissions from metro electricity use. It finds a net saving of 155 t CO₂/day and substantial CO and HC reductions, but smaller NOₓ and PM savings, with results highly sensitive to modal shift composition, electricity source, and ridership.
Key findings
- With projected ridership of 1.56 million daily passengers, the metro yields a net reduction of 155 tonnes CO₂/day, plus daily savings of 3871 kg CO, 2526 kg HC, 133 kg NOₓ, and 82 kg PM.
- Metro operation emits 389 t/day CO₂ compared with 544 t/day avoided from shifted vehicles; avoided emissions are largest from two-wheelers (12–48%), auto-rickshaws (19–47%), and taxis (5–34%), with buses (9–14%) and cars (4–29%) contributing moderately.
- Scenario analysis shows the greatest net savings for CO₂, CO, PM, and HC when modal shift is dominated by private cars and two-wheelers (Scenario 2), while solar-only power (Scenario 3) gives the highest NOₓ savings and second-best CO₂ savings.
- Grid-only electricity (Scenario 4) performs worst, producing negative net savings for CO₂ and NOₓ; if daily ridership drops below 1.1 million, avoided emissions fall below metro operation emissions.
Methods
- Modal shift analysis used projected ridership of 1.56 million daily passengers and mode-shift shares from a recent Mumbai Metro study: bus 28%, suburban train 27%, two-wheelers 20%, auto-rickshaws 9%, private cars 8%, and taxis 8%.
- Avoided emissions were estimated by converting shifted commuters to equivalent on-road vehicles using average occupancy, then applying fuel-type, vintage/BS-norm distribution, a 12 km average trip length, and weighted emission factors derived from vehicle registration data and national inventories.
- Metro operational emissions were based on 1207 MWh/day electricity demand (437 MWh/day traction, 770 MWh/day auxiliary), modeled with GaBi and CML methods under a 50:50 grid–solar electricity mix; scenario analysis varied modal shift, power source, and ridership.
Limitations
- The authors state the study relied on secondary mode-shift data and projected ridership, which may not reflect actual commuter behavior; they recommend future primary household/commuter surveys and observed ridership data from the metro operator.
- The authors note that excluding fuel production impacts may have underestimated emission reduction potential, and that access/egress trips could significantly increase overall metro journey emissions; future studies should adopt a door-to-door perspective.
- The text also makes evident further assumptions: BS-VI emission factors were estimated because they were not readily available, and no significant seasonal variation in occupancy levels was assumed.
Model-written summary. Check it against the paper before relying on it.
Integrity signals
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Cites
Statistics
Claims the paper makes
1 of 6 cited sources checked · 0 supported · 0 flagged · accuracy not yet measured
- Findingown data
In scenario 2 (greater shift from private cars), net emission savings are highest across all evaluated scenarios.
“As shown in Fig. 3, a greater shift from private cars (scenario 2) results in the highest net emission savings across all evaluated scenarios.”
Quote in the paperSubstantial claim - Findingown data
Emission savings are sensitive to metro ridership levels.
“Lastly, Scenario 5 highlights the sensitivity of emission savings to metro ridership levels.”
Quote in the paperSubstantial claim - Findingown data
The metro system yields a daily net saving of 133 kg of NOx.
“133 kg of NO x”
Quote in the paperSubstantial claim- The authors state this as an assumption: A daily ridership of 1.6 million passengers is the baseline for calculations.
- The authors state this as an assumption: The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
- The authors state this as an assumption: An average trip length of 12 km per commuter is adopted from official reports for Mumbai Metro Line 3.
- Findingown data
Shifting vehicles from taxis contributed 5-34% of the emission reductions.
“The greatest emission reductions were achieved by shifting vehicles from two-wheelers (12-48%), auto-rickshaws (19-47%), and taxis (5-34%), owing to their high emission intensity, while buses (9-14%) and cars (4-29%) contributed moderately.”
Quote in the paperSubstantial claim- The authors state this as an assumption: A daily ridership of 1.6 million passengers is the baseline for calculations.
- The authors state this as an assumption: The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
- Findingreasoning
The greatest emission reductions occur from replacing high-frequency, low-occupancy, and poorly regulated vehicle modes.
“The greatest emission reductions occur from replacing high-frequency, low-occupancy, and poorly regulated vehicle modes.”
Quote in the paperSubstantial claim
- Findingown data
Scenario 3 delivers the second-best CO2 savings.
“Scenario 3 delivers the highest NO x savings, and the second-best for CO 2 .”
Quote in the paperNot a substantial claim - Findingreasoning
About 90% of auto-rickshaws still belong to BS-III or BS-IV emission norms.
“about 90% of auto-rickshaws and 67% of two-wheelers still belong to these emission norms”
Quote in the paperSubstantial claim - Findingreasoning
There is a relatively lower net saving in NOx and PM emissions than in other pollutants.
“However, there is a relatively lower net saving in NOx and PM emissions.”
Quote in the paperSubstantial claim - Findingown data
Shifting vehicles from buses contributed 9-14% of the emission reductions.
“The greatest emission reductions were achieved by shifting vehicles from two-wheelers (12-48%), auto-rickshaws (19-47%), and taxis (5-34%), owing to their high emission intensity, while buses (9-14%) and cars (4-29%) contributed moderately.”
Quote in the paperNot a substantial claim- The authors state this as an assumption: A daily ridership of 1.6 million passengers is the baseline for calculations.
- The authors state this as an assumption: The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
- Findingreasoning
The metro system yields a net reduction of 155 tonnes of CO2 per day after subtracting metro operational emissions from avoided on-road emissions.
“The results show a net reduction of 155 tonnes of CO 2 per day”
- Also stated in: § 4.3 Net emissions saved from the operation of the metro system · plain
“with a net saving of 155 t/day.”
Quote in the paperSubstantial claim- The authors state this as an assumption: A daily ridership of 1.6 million passengers is the baseline for calculations.
- The authors state this as an assumption: The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
- The authors state this as an assumption: An average trip length of 12 km per commuter is adopted from official reports for Mumbai Metro Line 3.
- The authors state this as an assumption: The metro system sources electricity from a 50:50 mix of grid electricity and solar power.
- Also stated in: § 4.3 Net emissions saved from the operation of the metro system · plain
- Findingnone given
The operation of the metro line emits 389 tonnes of CO2 per day.
“the operation of the metro line will emit 389 t/day of CO 2 emissions”
Quote in the paperSubstantial claim- The authors state this as an assumption: The operational energy demand is estimated using the design specifications of Mumbai Metro Line 3.
- The authors state this as an assumption: The metro system sources electricity from a 50:50 mix of grid electricity and solar power.
- Findingown data
In terms of CO2, petrol cars account for 17% of the emissions reduction.
“In terms of CO 2 , the largest share of emissions reduction stems from taxis (21%), auto-rickshaws (19%), and petrol cars (17%).”
Quote in the paperNot a substantial claim- The authors state this as an assumption: A daily ridership of 1.6 million passengers is the baseline for calculations.
- The authors state this as an assumption: The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
- Findingown data
Shifting vehicles from cars contributed 4-29% of the emission reductions.
“The greatest emission reductions were achieved by shifting vehicles from two-wheelers (12-48%), auto-rickshaws (19-47%), and taxis (5-34%), owing to their high emission intensity, while buses (9-14%) and cars (4-29%) contributed moderately.”
Quote in the paperSubstantial claim- The authors state this as an assumption: A daily ridership of 1.6 million passengers is the baseline for calculations.
- The authors state this as an assumption: The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
- Findingown data
CNG cars contribute 10% of NOx emissions.
“The NOx emissions are largely contributed by taxis (34%), two-wheelers (28%), CNG cars (10%), with CNG buses accounting for another 7%.”
Quote in the paperNot a substantial claim- The authors state this as an assumption: A daily ridership of 1.6 million passengers is the baseline for calculations.
- The authors state this as an assumption: The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
- Findingown data
In terms of CO2, taxis account for 21% of the emissions reduction.
“In terms of CO 2 , the largest share of emissions reduction stems from taxis (21%), auto-rickshaws (19%), and petrol cars (17%).”
Quote in the paperNot a substantial claim- The authors state this as an assumption: A daily ridership of 1.6 million passengers is the baseline for calculations.
- The authors state this as an assumption: The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
- Findingown data
Shifting vehicles from two-wheelers contributed 12-48% of the emission reductions.
“The greatest emission reductions were achieved by shifting vehicles from two-wheelers (12-48%), auto-rickshaws (19-47%), and taxis (5-34%), owing to their high emission intensity, while buses (9-14%) and cars (4-29%) contributed moderately.”
Quote in the paperSubstantial claim- The authors state this as an assumption: A daily ridership of 1.6 million passengers is the baseline for calculations.
- The authors state this as an assumption: The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
- Findingreasoning
Scenario 1 shows the least overall mitigation.
“In contrast, scenario 1 shows the least overall mitigation.”
Quote in the paperSubstantial claim - Findingreasoning
Autorickshaws account for only 9% of the shift, yet they contribute 19-47% of avoided emissions.
“The results showed that the autorickshaws account for only 9% of the shift, yet they contribute 19-47% of avoided emissions.”
Quote in the paperSubstantial claim - Findingreasoning
About 67% of two-wheelers still belong to BS-III or BS-IV emission norms.
“about 90% of auto-rickshaws and 67% of two-wheelers still belong to these emission norms”
Quote in the paperSubstantial claim - Findingreasoning
The mode shift from two-wheelers reduces 12-48% of avoided emissions, despite their 20% share in the mode shift.
“Similarly, the mode shift from two-wheelers reduces 12-48% of avoided emissions, despite their 20% share in the mode shift.”
Quote in the paperSubstantial claim - Findingown data
Two-wheelers contribute 28% of NOx emissions.
“The NOx emissions are largely contributed by taxis (34%), two-wheelers (28%), CNG cars (10%), with CNG buses accounting for another 7%.”
Quote in the paperSubstantial claim- The authors state this as an assumption: A daily ridership of 1.6 million passengers is the baseline for calculations.
- The authors state this as an assumption: The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
- Findingnone given
Buses contribute significantly to CO2, HC, and NOx reductions.
“Furthermore, the buses contribute significantly to CO 2 , HC, and NO x reductions.”
Quote in the paperNot a substantial claim - Findingown data
The vehicles shifted from the road would have emitted 544 tonnes of CO2 per day.
“compared to 544 t/day saved due to the shift of the vehicles”
Quote in the paperSubstantial claim- The authors state this as an assumption: A daily ridership of 1.6 million passengers is the baseline for calculations.
- The authors state this as an assumption: The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
- The authors state this as an assumption: An average trip length of 12 km per commuter is adopted from official reports for Mumbai Metro Line 3.
- Findingown data
Approximately 64% of the metro system's electricity is consumed for auxiliary functions.
“Approximately 64% of electricity is consumed for auxiliary functions, whereas the remaining is used for train operations.”
Quote in the paperSubstantial claim - Findingown data
Shifting vehicles from auto-rickshaws contributed 19-47% of the emission reductions.
“The greatest emission reductions were achieved by shifting vehicles from two-wheelers (12-48%), auto-rickshaws (19-47%), and taxis (5-34%), owing to their high emission intensity, while buses (9-14%) and cars (4-29%) contributed moderately.”
Quote in the paperSubstantial claim- The authors state this as an assumption: A daily ridership of 1.6 million passengers is the baseline for calculations.
- The authors state this as an assumption: The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
- Findingown data
In terms of CO2, auto-rickshaws account for 19% of the emissions reduction.
“In terms of CO 2 , the largest share of emissions reduction stems from taxis (21%), auto-rickshaws (19%), and petrol cars (17%).”
Quote in the paperNot a substantial claim- The authors state this as an assumption: A daily ridership of 1.6 million passengers is the baseline for calculations.
- The authors state this as an assumption: The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
- Findingown data
The metro system yields a daily net saving of 2526 kg of HC.
“2526 kg of HC”
- Also stated in: § 4.3 Net emissions saved from the operation of the metro system · plain
“The metro operation reduced other pollutants like CO and HC significantly by 3871 kg and 2526 kg, respectively.”
Quote in the paperSubstantial claim- The authors state this as an assumption: A daily ridership of 1.6 million passengers is the baseline for calculations.
- The authors state this as an assumption: The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
- The authors state this as an assumption: An average trip length of 12 km per commuter is adopted from official reports for Mumbai Metro Line 3.
- Also stated in: § 4.3 Net emissions saved from the operation of the metro system · plain
- Findingown data
The metro system yields a daily net saving of 82 kg of PM.
“82 kg of PM”
Quote in the paperSubstantial claim- The authors state this as an assumption: A daily ridership of 1.6 million passengers is the baseline for calculations.
- The authors state this as an assumption: The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
- The authors state this as an assumption: An average trip length of 12 km per commuter is adopted from official reports for Mumbai Metro Line 3.
- Findingreasoning
Scenario 3 delivers the highest NOx savings.
“Scenario 3 delivers the highest NO x savings, and the second-best for CO 2 .”
Quote in the paperSubstantial claim - Findingown data
If daily metro ridership drops below 1.1 million, the emissions avoided because of the shift from other modes will be lower than the emissions of metro operation.
“As shown in Fig. 4, if the daily metro ridership drops below 1.1 million, the emissions avoided because of the shift from other modes will be lower than the emissions of metro operation.”
- Also stated in: § 4.4 Scenario analysis · boosted
“The present study also concluded that when the daily metro ridership drops below 1.1 million, the emissions avoided because of the shift from other modes will be lower than the emissions of metro operation.”
Quote in the paperSubstantial claim - Also stated in: § 4.4 Scenario analysis · boosted
- Findingreasoning
Scenario 4 performs the worst across most indicators, including negative net savings for CO2 and NOx.
“In stark contrast, scenario 4 performs the worst across most indicators, including negative net savings for CO 2 and NO x .”
Quote in the paperSubstantial claim - Findingnone given
Net emissions saved per day are substantial when compared against emissions from metro operations.
“When compared against the emissions from metro operations, the net emissions saved per day are substantial.”
Quote in the paperSubstantial claim - Findingown data
CNG buses contribute 7% of NOx emissions.
“The NOx emissions are largely contributed by taxis (34%), two-wheelers (28%), CNG cars (10%), with CNG buses accounting for another 7%.”
Quote in the paperNot a substantial claim- The authors state this as an assumption: A daily ridership of 1.6 million passengers is the baseline for calculations.
- The authors state this as an assumption: The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
- Findingown data
Taxis contribute 34% of NOx emissions.
“The NOx emissions are largely contributed by taxis (34%), two-wheelers (28%), CNG cars (10%), with CNG buses accounting for another 7%.”
Quote in the paperSubstantial claim- The authors state this as an assumption: A daily ridership of 1.6 million passengers is the baseline for calculations.
- The authors state this as an assumption: The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
- Findingown data
The metro system yields a daily net saving of 3871 kg of CO.
“daily savings of 3871 kg of CO”
- Also stated in: § 4.3 Net emissions saved from the operation of the metro system · plain
“The metro operation reduced other pollutants like CO and HC significantly by 3871 kg and 2526 kg, respectively.”
Quote in the paperSubstantial claim- The authors state this as an assumption: A daily ridership of 1.6 million passengers is the baseline for calculations.
- The authors state this as an assumption: The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
- The authors state this as an assumption: An average trip length of 12 km per commuter is adopted from official reports for Mumbai Metro Line 3.
- Also stated in: § 4.3 Net emissions saved from the operation of the metro system · plain
- Findingown data
Emission reduction benefits are highly sensitive to energy mix and ridership levels.
“However, the scenario analysis showed that the emission reduction benefits are highly sensitive to energy mix and ridership levels.”
Quote in the paperSubstantial claim - Findingnone given
In PM emissions, two-wheelers (48%) and auto-rickshaws (40%) show similar dominance.
“A similar dominance of two-wheelers (48%) and autorickshaws (40%) is observed in PM emissions.”
Quote in the paperNot a substantial claim - Findingown data
The pattern of contributions shifts significantly when evaluating avoided carbon monoxide (CO) emissions.
“The pattern shifts significantly when evaluating avoided carbon monoxide (CO) emissions.”
Quote in the paperNot a substantial claim - Interpretationreasoning
The greatest emission reductions were achieved by shifting vehicles from two-wheelers, auto-rickshaws, and taxis, owing to their high emission intensity.
“The greatest emission reductions were achieved by shifting vehicles from two-wheelers (12-48%), auto-rickshaws (19-47%), and taxis (5-34%), owing to their high emission intensity, while buses (9-14%) and cars (4-29%) contributed moderately.”
Quote in the paperSubstantial claim - Interpretationown data
Incentivizing private car and two-wheeler users to adopt the metro rail offers the most substantial environmental benefit.
“It emphasizes that incentivizing private car and two-wheeler users to adopt the metro rail offers the most substantial environmental benefit.”
Quote in the paperSubstantial claim - Interpretationreasoning
Clean electricity sources play a critical role in enhancing the environmental performance of metro systems.
“This scenario underscores the critical role of clean electricity sources in enhancing the environmental performance of metro systems.”
Quote in the paperSubstantial claim - Interpretationown data
Metro operations that rely exclusively on carbon-intensive power sources are unsustainable.
“This scenario highlights the unsustainability of metro operations that rely exclusively on carbon-intensive power sources.”
Quote in the paperSubstantial claim - Interpretationown data
The metro effectively replaces emissions from a wide range of on-road vehicles.
“The metro effectively replaces emissions from a wide range of on-road vehicles.”
Quote in the paperSubstantial claim- The authors state this as an assumption: The mode shift to metro leads to a decrease in the equivalent number of on-road vehicles and suburban trains.
- Interpretationown data
The modal shift from conventional on-road transport to an electrified underground metro system presents a substantial opportunity for mitigating urban emissions in Mumbai.
“The modal shift from conventional on-road transport to an electrified underground metro system presents a substantial opportunity for mitigating urban emissions in Mumbai.”
Quote in the paperSubstantial claim - Premisecitation
The total operational energy demand of the metro system is 1207 MWh/day.
“The total operational energy demand of the metro system was estimated to be 1207 MWh/day [13].”
Quote in the paperSubstantial claim0 of 1 sources checked- cites [13] Shinde AM, Dikshit AK, Soni A. Environmental life cycle assessment of underground metro rail: a case study in Mumbai Metropolitan Region, India. Environ Impact Assess Rev. 2024. https://doi.org/10.1016/j.eiar.2024.107501. source
- The authors state this as an assumption: The operational energy demand is estimated using the design specifications of Mumbai Metro Line 3.
- Interpretationreasoning
Even limited reductions in usage of high-emission modes can lead to considerable emissions savings due to their poor fuel efficiency and high usage rates.
“This indicates that even limited reductions in usage of high-emission modes can lead to considerable emissions savings due to their poor fuel efficiency and high usage rates.”
Quote in the paperSubstantial claim - Interpretationreasoning
The true climate and air quality benefits of the metro system are maximized when it is coupled with a renewable power supply.
“The true climate and air quality benefits of the metro system are maximized when it is coupled with a renewable power supply.”
Quote in the paperSubstantial claim - Interpretationreasoning
The mitigation potential of metro rail could be profoundly enhanced by utilizing solar power for traction and auxiliary purposes.
“The mitigation potential of metro rail could be profoundly enhanced by utilizing solar power for traction and auxiliary purposes.”
Quote in the paperSubstantial claim - Interpretationreasoning
The metro rail system in congested urban areas like Mumbai has multifaceted environmental benefits.
“The overall emission reduction potential underscores the multifaceted environmental benefit of the metro rail system in congested urban areas like Mumbai.”
Quote in the paperSubstantial claim - Interpretationown data
The mitigation potential of metro rail is highly sensitive to modal shift, source of electricity used, and daily ridership levels.
“However, the mitigation potential of metro rail is highly sensitive to key variables, such as modal shift, source of electricity used, and daily ridership levels.”
Quote in the paperSubstantial claim- The authors state this as an assumption: Scenario 1 assumes a greater shift from public bus transport (70%) and a slightly reduced shift from the rest of the modes.
- The authors state this as an assumption: Scenario 2 assumes the metro's mode shift is dominated by cars and two-wheelers.
- The authors state this as an assumption: Scenario 3 models the metro powered entirely by solar energy.
- The authors state this as an assumption: Scenario 4 models the metro powered solely by conventional grid electricity.
- The authors state this as an assumption: Scenario 5 assumes a 10% rise in daily metro passengers compared to the baseline.
- Interpretationreasoning
Replacing already low-emission modes, such as buses and suburban trains, with metro use has limited marginal benefit.
“This outcome highlights a limited marginal benefit of replacing already low-emission modes, such as buses and suburban trains, with metro use.”
Quote in the paperSubstantial claim - Interpretationown data
The benefits of the new metro rail could be further increased by encouraging a larger mode shift from private vehicles compared to public transportation.
“The scenario analysis demonstrated that the benefits of the new metro rail could be further increased by encouraging the larger mode shift from private vehicles compared to public transportation.”
Quote in the paperSubstantial claim - Interpretationreasoning
The relatively low particulate and hydrocarbon outputs of the metro suggest strong mitigation potential in terms of air quality.
“The relatively low particulate and hydrocarbon outputs suggest strong mitigation potential in terms of air quality.”
Quote in the paperSubstantial claim - Interpretationreasoning
Taxis, auto-rickshaws, and petrol cars together account for more than half of the total CO2 emissions avoided.
“These three vehicle categories together account for more than half of the total CO 2 emissions avoided.”
Quote in the paperNot a substantial claim - Interpretationreasoning
The significant contribution from two-wheelers and auto-rickshaws underscores their environmental burden on urban air quality.
“The significant contribution from two-wheelers and auto-rickshaws underscores their environmental burden on urban air quality.”
Quote in the paperNot a substantial claim- Rests on an assumption: HC emissions primarily result from unburned fuel and are a key component of ground-level ozone formation.
- May combine two claims. 12
- Classified as probably not a substantial claim. 13
May combine two claims.
InterpretationcitationThe sharp decline in vehicular emissions will improve air quality, reducing the risk of respiratory conditions such as asthma and bronchitis and mitigating the overall burden of air pollution-related health issues.
“The sharp decline in vehicular emissions will result in improved air quality, thus reducing the risk of respiratory conditions such as asthma and bronchitis, and mitigating the overall burden of air pollution-related health issues [29,51].”
Quote in the paperNot a substantial claim1 of 2 sources checked- cites [29] Abhijna M, Rao KVK, Perumal V. How new metro lines shape a sustainable future: a before-after study of travel behavior, perceptions, and emissions in Mumbai Metropolitan Region, India. Sustain Cities Soc. 2025. https://doi.org/10.1016/j.scs.2025.106431. source
- cites [51] Jain S, Barthwal V. Health impact assessment of auto rickshaw and cab drivers due to exposure to vehicular pollution in Delhi: an integrated approach. Environ Sci Pollut Res Int. 2022;29:5124–33. https://doi.org/10.1007/s11356-021-16058-9. source
The Introduction identifies vehicular emissions as a source of urban air pollution, and the Conclusion associates traffic emissions with respiratory problems including asthma. The paper does not establish that a sharp decline in emissions will improve air quality or reduce the overall health burden, and the cited passages do not mention bronchitis. (LLM, conf=0.85)
Experimental — accuracy not yet measured
May combine two claims.
Findingnone givenElectricity supplied solely from the grid could cause an additional emission burden compared to the baseline scenario, resulting in negative net savings for CO2 and NOx.
“However, the electricity supplied solely from the grid could cause an additional emission burden than the baseline scenario, resulting in negative net savings for CO 2 and NO x .”
Quote in the paperSubstantial claimMay combine two claims.
FindingreasoningScenario 2 demonstrates the greatest mitigation potential for CO2, CO, PM, and HC, but not NOx.
“Scenario 2 demonstrates the greatest mitigation potential for CO 2 , CO, PM, and HC, but not NO x .”
Quote in the paperSubstantial claimMay combine two claims.
FindingreasoningSuburban trains and buses account for more than half of the modal split, but they contribute only 19% of CO2 savings.
“Although suburban trains and buses account for more than half of the modal split, they contribute only 19% of CO 2 savings.”
Quote in the paperSubstantial claimMay combine two claims.
FindingreasoningFor avoided CO emissions, two-wheelers are the highest contributor (47%), followed by petrol cars (22%) and auto-rickshaws (20%).
“Here, two-wheelers emerge as the highest contributor (47%), followed by petrol cars (22%), and auto-rickshaws (20%), which would be saved due to the operation of metro rail.”
Quote in the paperNot a substantial claimMay combine two claims.
Findingnone givenFor HC emissions, auto-rickshaws are the largest contributor (47%), followed by two-wheelers (21%) and taxis (14%).
“For HC emissions, auto-rickshaws are the largest contributor (47%), followed by twowheelers (21%), and taxis (14%), resulting in the highest avoided HC emissions from auto-rickshaws, followed by two-wheelers and taxis.”
Quote in the paperSubstantial claimProbably not a substantial claim: may not pass S3 (load-bearing).
Interpretationown dataThe combined 29% share from cars emphasizes the importance of shifting personal vehicle users to the metro rail.
“The combined 29% share from cars also emphasizes the importance of shifting personal vehicle users to the metro rail.”
Quote in the paperNot a substantial claimProbably not a substantial claim: may not pass S3 (load-bearing).
PremisecitationSoni and Chandel [25] found that the reduction in CO2 emissions would be greater if the shift were from private vehicles to the metro.
“Soni and Chandel [25] also found that the reduction in CO 2 emissions would be greater if the shift were from private vehicles to the metro.”
Quote in the paperNot a substantial claim0 of 1 sources checked- cites Soni and Chandel [25] Soni AR, Chandel MK. Assessment of emission reduction potential of Mumbai metro rail. J Clean Prod. 2018;197:1579–86. https://doi.org/10.1016/j.jclepro.2018.06.216. source
Classified as probably not a substantial claim.
InterpretationreasoningElectric traction minimizes tailpipe-related pollutants.
“This also reflects the advantage of electric traction in minimizing tailpipe-related pollutants.”
Quote in the paperSubstantial claimMay combine two claims.
InterpretationreasoningThe highest avoided NOx emission is contributed by taxis, followed by two-wheelers and CNG cars.
“Therefore, the highest avoided NOₓ emission is contributed by taxis, followed by the two-wheelers and CNG cars.”
Quote in the paperSubstantial claimMay combine two claims.
Interpretationown dataA greater shift from private vehicles and increased reliance on renewable electricity can further enhance mitigation.
“Scenario analysis revealed that a greater shift from private vehicles and increased reliance on renewable electricity can further enhance mitigation.”
Quote in the paperSubstantial claim- The authors state this as an assumption: Scenario 1 assumes a greater shift from public bus transport (70%) and a slightly reduced shift from the rest of the modes.
- The authors state this as an assumption: Scenario 2 assumes the metro's mode shift is dominated by cars and two-wheelers.
- The authors state this as an assumption: Scenario 3 models the metro powered entirely by solar energy.
- The authors state this as an assumption: Scenario 4 models the metro powered solely by conventional grid electricity.
- The authors state this as an assumption: Scenario 5 assumes a 10% rise in daily metro passengers compared to the baseline.
Classified as probably not a substantial claim.
InterpretationreasoningSustaining and increasing ridership is important to maximize the metro's climate and air quality benefits.
“This finding emphasizes the importance of sustaining and increasing ridership to maximize the metro's climate and air quality benefits.”
Quote in the paperSubstantial claimMay combine two claims.
InterpretationreasoningSuburban trains and buses have lower fuel consumption and emissions per passenger-kilometer.
“This reflects their lower fuel consumption and emissions per passenger-kilometer.”
Quote in the paperSubstantial claimProbably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.
InterpretationreasoningThe sharp decline in vehicular air pollution will result in improved health of the people in Mumbai, reducing the risk of respiratory conditions such as asthma and bronchitis, and other air pollution-related health issues.
“The sharp decline in vehicular air pollution will result in improved health of the people in Mumbai, reducing the risk of respiratory conditions such as asthma and bronchitis, and other air pollutionrelated health issues.”
Quote in the paperNot a substantial claimClassified as probably not a substantial claim.
Study design and conductreasoningThese projections may not accurately reflect actual commuter behavior.
“However, these projections may not accurately reflect actual commuter behavior.”
Quote in the paperSubstantial claim- Rests on an assumption: Actual ridership can vary due to factors such as service reliability, affordability, connectivity, and commuter preferences.
Classified as probably not a substantial claim.
Study design and conductnone givenThe present study relied on secondary mode shift data obtained from a recent study of the Mumbai Metro.
“The present study relied on secondary mode shift data obtained from a recent study of the Mumbai Metro.”
Quote in the paperSubstantial claimProbably not a substantial claim: may not pass S3 (load-bearing).
Study design and conductnone givenThe exclusion of fuel production impacts might have underestimated the emission reduction potential of the metro.
“The exclusion of fuel production impacts might have underestimated the emission reduction potential of the metro.”
Quote in the paperNot a substantial claimClassified as probably not a substantial claim.
Study design and conductnone givenThe present study also relied on projected ridership figures obtained from earlier studies.
“The present study also relied on projected ridership figures obtained from earlier studies.”
Quote in the paperSubstantial claimMay combine two claims.
PremisecitationThe operational energy demand includes 437 MWh/day for traction and 770 MWh/day for auxiliary functions.
“This includes 437 MWh/day for traction (train movement) and 770 MWh/day for auxiliary functions”
Quote in the paperSubstantial claim0 of 1 sources checked- cites [13] Shinde AM, Dikshit AK, Soni A. Environmental life cycle assessment of underground metro rail: a case study in Mumbai Metropolitan Region, India. Environ Impact Assess Rev. 2024. https://doi.org/10.1016/j.eiar.2024.107501. source
- The authors state this as an assumption: The operational energy demand is estimated using the design specifications of Mumbai Metro Line 3.
Probably not a substantial claim: may not pass S3 (load-bearing).
InterpretationreasoningThe distribution of CO emissions reflects the dominance of small, gasoline-powered engines in Mumbai's vehicle fleet.
“This distribution reflects the dominance of small, gasoline-powered engines in Mumbai's vehicle fleet.”
Quote in the paperNot a substantial claimProbably not a substantial claim: may not pass S3 (load-bearing).
PremisecitationIn Delhi, CO emissions were mostly contributed by two-wheelers and cars.
“Singh et al. [49] reported similar findings where CO emissions were mostly contributed by two-wheelers and cars in Delhi, India.”
Quote in the paperNot a substantial claim0 of 1 sources checked- cites Singh et al. [49] Singh V, Sahu SK, Kesarkar AP, Biswal A. Estimation of high resolution emissions from road transport sector in a megacity Delhi. Urban Clim. 2018;26:109–20. https://doi.org/10.1016/j.uclim.2018.08.011. source
Probably not a substantial claim: may not pass S3 (load-bearing).
InterpretationreasoningThe relatively lower CO contribution from buses and taxis suggests a more regulated CO emission profile for these commercial vehicles.
“The relatively lower CO contribution from buses and taxis suggests a more regulated CO emission profile for these commercial vehicles.”
Quote in the paperNot a substantial claimProbably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.
Interpretationnone givenSmall gasoline-powered vehicles are often poorly maintained and exhibit inefficient combustion, resulting in high CO emissions.
“These vehicles are often poorly maintained and exhibit inefficient combustion, resulting in high CO emissions.”
Quote in the paperNot a substantial claim
The authors state this as an assumption.
A daily ridership of 1.6 million passengers is the baseline for calculations.
“A daily ridership of 1.6 million passengers (as projected by official reports) is considered as the baseline for calculations.”
The authors state this as an assumption.
The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.
“The mode shift shares from cars, buses, suburban trains, two-wheelers, autorickshaws, and taxis are adopted from a recent mode shift study for the Mumbai Metro.”
The authors state this as an assumption.
BS-VI emission factors are derived by applying the percent reduction reported for BS-IV vehicles in official government reports.
“Since emission factors for BS-VI vehicles are not readily available, this study adopts an estimation approach.The percent reduction reported for BS-IV vehicles in official government reports is applied to derive BS-VI emission factors.”
The authors state this as an assumption.
Occupancy rates for private and public transport modes are taken from existing literature and government datasets, and no significant seasonal variation in occupancy levels is assumed.
“Occupancy rates for private and public transport modes are taken from existing literature and government datasets.No significant seasonal variation in occupancy levels is assumed in this study.”
The authors state this as an assumption.
An average trip length of 12 km per commuter is adopted from official reports for Mumbai Metro Line 3.
“An average trip length of 12 km per commuter is adopted from official reports for Mumbai Metro Line 3.”
The authors state this as an assumption.
The operational energy demand is estimated using the design specifications of Mumbai Metro Line 3.
“The operational energy demand is estimated using the design specifications of Mumbai Metro Line 3.”
The authors state this as an assumption.
The metro system sources electricity from a 50:50 mix of grid electricity and solar power.
“The metro system is assumed to source electricity from a 50:50 mix of grid electricity and solar power.”
The authors state this as an assumption.
The mode shift to metro leads to a decrease in the equivalent number of on-road vehicles and suburban trains.
“It has been assumed that the mode shift to metro leads to a decrease in the equivalent number of on-road vehicles, as well as suburban trains.”
The paper relies on this without support.
Many on-road vehicles are equipped with advanced after-treatment technologies such as selective catalytic reduction and diesel particulate filter, which effectively reduce NOx and PM emissions.
“This is primarily because many on-road vehicles are equipped with advanced after-treatment technologies such as selective catalytic reduction and diesel particulate filter, which effectively reduce these emissions.”
The authors state this as an assumption.
Scenario 1 assumes a greater shift from public bus transport (70%) and a slightly reduced shift from the rest of the modes.
“Scenario 1 assumes a greater shift from public bus transport (70%) and a slightly reduced shift from the rest of the modes, as shown in Table 6.”
The authors state this as an assumption.
Scenario 2 assumes the metro's mode shift is dominated by cars and two-wheelers.
“In scenario 2, the metro's mode shift is assumed to be dominated by cars and two-wheelers.”
The authors state this as an assumption.
Scenario 3 models the metro powered entirely by solar energy.
“Scenario 3 models the metro powered entirely by solar energy.”
The authors state this as an assumption.
Scenario 4 models the metro powered solely by conventional grid electricity.
“Conversely, scenario 4 presents the worst-case scenario, in which the metro system is powered solely by conventional grid electricity.”
The authors state this as an assumption.
Scenario 5 assumes a 10% rise in daily metro passengers compared to the baseline.
“It assumes a 10% rise in daily metro passengers compared to the baseline.”
The paper relies on this without support.
Actual ridership can vary due to factors such as service reliability, affordability, connectivity, and commuter preferences.
“The actual ridership can vary due to factors such as service reliability, affordability, connectivity, and commuter preferences.”
The paper relies on this without support.
HC emissions primarily result from unburned fuel and are a key component of ground-level ozone formation.
“HC emissions primarily result from unburned fuel and are a key component of ground-level ozone formation.”
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Cited by
Sorted by citations
Das, A., David, J. R., Swaminathan, P. P., Chandrasekarabarathi, S., Sudarsan, J. S., & Parthiban, P. (2026) · Scientific Reports · doi:10.1038/s41598-026-45731-7
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- Authors
- Aryan, Y., Shinde, A. M., & Dikshit, A. K.
- Affiliations
- Indian Institute of Technology Bombay (IN)
- Manipal Academy of Higher Education (IN)
- Corresponding author
- Shinde, Amar Mohan
- Venue
- Discover Sustainability
- Published
- 2025-10-31
- Volume
- 6
- Issue
- 1
- ISSN
- 2662-9984 (ISSN-L)
- OpenAlex
- W4415728767
- Semantic Scholar
- 00e1d97c6763f832bcf611045cb0e21b4cf7f4b4
- Cited by
- 3
- References
- 29
- Citations by year
- 2026: 3
- FWCI
- 0.73
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Locations
- Discover Sustainability (publishedVersion, cc-by)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
- Topics
- Physical Sciences › Engineering › Automotive Engineering › Vehicle emissions and performance
- Social Sciences › Transportation › Transportation Planning and Optimization
- Physical Sciences › Energy › Renewable Energy, Sustainability and the Environment › Energy, Environment, and Transportation Policies
- Keywords
- modal shift, greenhouse gas emissions, air pollutant emissions, avoided emissions, on-road vehicle emissions, grid electricity, ridership, vehicle occupancy, two-wheeled vehicles, auto-rickshaws, taxis, buses, carbon dioxide, nitrogen oxides, particulate matter, sustainable urban mobility, scenario analysis
About these checks
Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.
Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-11-06.
Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-11-06.
Cited sources are checked by gpt-6-sol.
Statistics and arithmetic are recomputed, not judged.
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