Vehicles top polluters in Delhi during Diwali week, says latest CSE assessment

High peak traffic for long hours due to surge in vehicle numbers 

Despite vehicles becoming the top polluter, action on transport remains the weakest

  • Among local pollution sources in Delhi, vehicles caused half of Delhi’s own contribution to PM2.5 during Diwali week (21-26 October)
  • When pollution concentration from all sources (local, NCR and beyond) are added, Delhi’s vehicles account for nearly 17 per cent of total PM2.5 concentration
  • High traffic load during Diwali week increased congestion for long hours -- from 12 noon to 8 pm -- flattening the congestion peaks
  • With high traffic on pre-Diwali days, average speed plummeted to 27 km per hour against the design standard of 60 km/hr or regulated speed of 40 km/hr. On some stretches this reduced to 17 km/hr
  • Nitrogen dioxide coming largely from vehicles correlates well with traffic peaks and congestion though dispersion helped to dilute it in the afternoons
  • A city with 1.4 crore vehicles and generating at least 276 lakh travel trips a day does not have scalable transportation solutions yet to reduce traffic volume
  • What is needed: public transport augmentation and integration, electrification of fleet, walking and cycling infrastructure, low emissions zones, vehicle restraint measures like parking caps and pricing, and transit-oriented development
  • Lack of sustainable alternatives blocking effective emergency measures to control vehicle usage during severe smog episodes in winter 

Find the complete analysis Click here

New Delhi, November 2, 2022: A CSE assessment of Diwali pollution levels in Delhi this year says that among the local pollution sources in the capital, vehicles were the main reason behind half of Delhi’s own contribution to PM2.5 concentration in the week of October 21-26. The substantial role of vehicles was evident in the day-long congestion that nearly erased the difference between peak and non-peak hours during that week. These indicative findings for the Diwali week of 2022 is also consistent with the findings of a similar analysis carried out for different phases of the previous year’s (2021) winter. 

“A city with 1.4 crore registered vehicles (as per the VAHAN database) and an annual addition of five lakh vehicles a year (of which 97 per cent are personal vehicles, mainly two-wheelers and cars), has failed to build transportation strategies to scale for transformative changes. With more than 200 lakh population (estimate of World Population Prospect by the UN, 2018), the city is estimated to be generating at least 276 lakh daily travel trips. If most of these commuting trips have to be self-organised with personal vehicles, Delhi cannot meet the clean air target or the benchmarks for liveability,” says Anumita Roychowdhury, executive director, research and advocacy, CSE. 

CSE’s assessment includes the following:

  • An analysis of the dynamic estimation of hourly source contribution to PM2.5 concentrations done by the Decision Support System (DSS) for Air Quality Management of the Indian Institute of Tropical Meteorology (IITM), Pune. This provides quantitative information on the contribution of emissions from Delhi’s own sources and the surrounding 19 districts in the National Capital Region (NCR) and beyond. This is an indicative trend as the data for October 22 and 26 is available until 14:30 hours and data for October 23 is available from 15:30 hours.
  • An analysis of hourly traffic speeds with the help of real time data from Google Maps to assess the level of congestion on 15 major arterial roads. The speed has been taken as a proxy for congestion and not to advocate high speed motorised traffic.
  • An analysis of real time hourly air quality data from the portal of Central Pollution Control Board to correlate pollution with the traffic build-up in the city. 

Key highlights of the CSE assessment 

Vehicles’ contribution to Delhi’s PM2.5 concentration was maximum during the week: Taken together with other sources (such as biomass and pollution from NCR and other districts plus Delhi’s own local sources), vehicles contributed nearly 17 per cent of the total PM2.5 concentration in the city. But if only Delhi’s local sources are considered, the transport sector topped the ranks (see Graph 1 in report), with vehicles contributing around half of the PM2.5 concentration from local sources. The indicative data shows that their daily share varied between 49.3 per cent to 53 per cent during that week. 

This was followed by household pollution (residential) at 13 per cent, industries at 11 per cent, construction at 7 per cent, waste burning and the energy sector at 5 per cent each, and road dust and other sources at 4 per cent each. “This observation is consistent with the trends evaluated during the previous winter in Delhi,” says Vivek Chattopadhyay, principal programme manager with CSE’s Clean Air and Sustainable Mobility unit.  

Combustion sources together have contributed more to PM2.5 concentration than dust sources: “The CSE report indicates that the overall share of all combustion sources – including vehicles, peripheral industries, the energy sector, waste burning and residential cooking -- have a higher share than the dust sources that include construction and road dust,” says Shambhavi Shukla, Programme Manager with CSE’s Clean Air and Sustainable Mobility unit. The report has used the DSS of IITM, which has provided the information on potential emission sources in Delhi, to reach at this conclusion. 

Sizeable pollution is coming from outside Delhi, requiring action at a regional scale -- but vehicles remain a challenge: The DSS estimation shows that during this phase, NCR districts accounted for 32.77 per cent of the concentration; other districts contributed 25.84 per cent, while biomass burning was responsible for 9.52 per cent. Says Roychowdhury: “This once again underscores the fact that the action will have to be scaled up across the region. But among all sources, transport is a substantial contributor in Delhi.” 

Choking congestion: CSE has further analysed the real time data from Google Maps for 15 major arterial roads to assess the hourly traffic speeds. The length of the roads selected are representative of the geographical spread. The travel time from origin to destination was noted for every hour from 8 AM to 9 PM for the period, which was later converted into speed in km/hour. The data was further analysed for traffic accumulation during peak and off-peak hours in the day. What the analysis shows: 

  • High congestion on all roads: Average speed on Delhi roads ranged from 27 kmph to 32 kmph in this week. The mean speed was 28 kmph against a designed speed of 60 kmph and regulated speed of 40km/h. Says Anannya Das, programme manager, sustainable mobility, CSE: “Here, speed has been taken as a proxy to understand the level of congestion and not to advocate high-speed vehicles or infrastructure in support of them.” This should not lead to more car-centric high speed corridors to promote motorised personal vehicles, but to augment public transport infrastructure to reduce volumes of traffic on road.
  • No distinct peak hours due to high traffic for long hours: Instead of two distinct traffic peaks during morning and evening, the duration of the congestion extended from 12 pm to 8 pm indicating high traffic accumulation. An 8-hour long traffic congestion indicates significant traffic accumulation and intensity.
  • Traffic build-up highest on pre-Diwali days: October 21 (Friday) and October 22 witnessed heavy congestion and average speed was observed at 23.7 and 23.8 kmph, respectively. On Diwali day of October 24 and post-Diwali day of October 25, when overall traffic reduces normally, average speed on road was relatively higher at 33 and 32 kmph, respectively. Diwali day had the least traffic build-up.
  • Congestion hotspots: While congestion had built up on all corridors, GT Karnal Road and Guru Ravidas Marg witnessed more congestion compared to others. The average speed on both was 17 kmph -- much lower than the mean speed observed on other roads during the period. Guru Ravidas Marg connects some of the densest settlements and is witness to ongoing metro construction. GT Karnal Road connects multiple business districts and high density residential settlements of north-west Delhi. Comparatively lower congestion was observed on MG Road and the Ring Road that had an average speed of 44 kmph and 41.7 kmph, respectively.
  • Hourly nitrogen dioxide levels correlate well with congestion in the city: CSE has further analysed the real time hourly nitrogen dioxide level as vehicles are responsible for substantial NO2 pollution in the city. The hourly level of NO2 correlated with congestion levels, though there have been dilutions due to dispersion during afternoons. Hourly NO2 levels in evenings were high, ranging between 73 µg/m³ to 86 µg/m³. This is the time when congestion is also high. There is also an inversion effect as the early morning and evening hours recorded high NO2 

Next steps: Need verifiable and measurable shift to public transport

Even though vehicles are the top polluters in Delhi, action to control their explosive numbers and usage have remained the slowest. Even the air emergency measures enforced for the very poor and severe categories of Air Quality Index (AQI) under the Graded Response Action Plan (GRAP) do not include action, barring increased parking charges, to reduce vehicle numbers on road to control smog episodes. This is primarily because of inadequate public transport systems, poor quality services, lack of last mile connectivity and restraint measures. 

Says Roychowdhury: “Even though action on transportation is underway, it is too little too late. Sustained and stringent action is needed for mobility transition. Otherwise, explosive vehicle numbers will negate the air quality gains of the leapfrog to Bharat Stage VI emissions standards.” 

Augment and improve service quality of buses: Steps have been taken to add new buses to the existing fleet recently, but the numbers are still inadequate. Retirement of old buses also limit the net addition. Delhi, with 7,320 buses currently, has close to 37 buses per lakh of population against the recommended 60 buses per lakh population (as per the service level benchmark of Ministry of Housing and Urban Affairs). Time-bound augmentation of the bus fleet and modernisation of bus services and infrastructure is needed to improve the quality of passenger services across the city. 

Ensure physical and fare integration of bus and metro systems: Though the process of physical integration of major metro stations with other modes of transport has started for seamless transfer, fare integration has not been possible yet and last mile connectivity with safe at-grade access for people needs immediate attention. 

Scale up walking and cycling infrastructure to connect neighbourhoods and implement low emissions zones: The Delhi government plans to redesign 500 km of PWD roads by 2023; the Delhi Development Authority (DDA) will add 200 km of dedicated corridors for pedestrians and cyclists. But the implementation that is underway needs scale and speed. The city also needs extensive networks of walking and cycling infrastructure to connect different neighbourhoods for functional usage at local levels. Though there are proposals to pedestrianise more streets/commercial areas, the full implementation has been possible only in Ajmal Khan Road and Shahajanabad. 

Immediately implement parking management area plans with parking caps and pricing in all municipal wards: Increasing parking rates during severely polluted days cannot work if the notified parking rules as a demand management measure and the Supreme Court directives to implement parking management area plans and parking pricing as per the rules are not implemented. This has not progressed beyond the three initial pilot schemes. Follow the parking rules under the Transit Oriented Development Policy within the influence zones of metro stations. Delhi needs congestion and pollution pricing and other restraint measures to control traffic volumes. 

Meet all milestones and targets set for implementation of electrification of the new vehicle fleet: The target for 25 per cent fleet electrification by 2024 is a good step forward. This needs acceleration. Promote low emissions zones linked to electric vehicles, walking and cycling and public transport access.

For more information, interviews etc, please contact Sukanya Nair:, 8816818864