Bengaluru’s Hebbal Tunnel Under Scrutiny: IIT-Bombay Study Faces Questions Over Data And Traffic Claims | Bengaluru-news News
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A new IIT-Bombay study was commissioned after criticism of Bengaluru’s Hebbal tunnel project. Now, IISc experts have questioned its data, methodology and traffic assessment
With construction already in progress, the debate around the Hebbal short tunnel is increasingly focused on the assumptions and information underpinning the traffic studies. (Representative Image)
Work on Bengaluru’s proposed Hebbal short tunnel has been progressing since June, but a traffic assessment commissioned by the Bangalore Development Authority (BDA) is now facing questions from transportation experts.
The study, conducted in August 2026, was undertaken after the tunnel proposal drew criticism from sections of the public. The report, titled Integrated Traffic Microsimulation Study – Bengaluru: Hebbal Flyover & Hebbal Short Tunnel, was authored by IIT-Bombay professor Archak Mittal for Rithwik Projects Private Limited.
While the BDA has cited the study as evidence supporting the need for the proposed tunnel and an elevated corridor, experts who have examined the report have raised concerns about the data used, the modelling approach and whether all relevant traffic scenarios were considered.
Questions Over The Traffic Data
Prof Ashish Verma, Convener of the IISc Sustainable Transportation Lab, said the IIT-Bombay assessment relied on traffic information contained in the DPRs supplied by the contractor. One issue highlighted in his review is the difference between the traffic speeds projected in the IIT-Bombay study and those mentioned in the Hebbal Short Tunnel DPR.
For the 2027 peak-hour Base Case, the IIT-B study gives a projected traffic speed of 13.74 kmph, while the DPR puts the corresponding figure at 4.29 kmph.
Verma also noted that the report does not provide comparative queue-length figures showing conditions before and after the proposed interventions. He further questioned the level of detail provided about the methodology used for the traffic simulation.
Concerns About The Mehkri Circle Flyover
The proposed elevated corridor at Mehkri Circle has also become a point of discussion. According to Verma’s review, the planned elevated road does not have a ramp for vehicles travelling straight towards Windsor Manor. As a result, vehicles making the relevant turn from Mehkri Circle could use the elevated route, while many vehicles continuing straight would still have to use the existing underpass.
Verma also sought greater clarity on how this elevated corridor would connect with the proposed east-west corridor linking Yeshwanthpur and KR Puram.
He questioned what would happen to traffic on surrounding roads if the proposed infrastructure simply shifts congestion from one location to another. He also said the environmental consequences of such traffic redistribution should form part of the assessment.
Four Scenarios Were Expected, Expert Says
Satyajit Arikutharam, former chief technical adviser to the Directorate of Urban Land Transport (DULT), raised another concern about the scope of the IIT-Bombay exercise. According to him, the assessment should have compared four situations:
- Existing conditions, or the Base Case
- The short tunnel by itself
- The elevated corridor by itself
- Both projects operating together
Arikutharam said the study instead examined only the Base Case and a scenario combining the tunnel and elevated corridor.
He also argued that the project’s requirement cannot be properly assessed using older traffic information. The DPR data predates the opening of an additional ramp at the Hebbal flyover in January 2026, meaning traffic patterns in the area have since changed.
Debate Over Passenger Car Unit Values
Another issue concerns the Passenger Car Unit (PCU) values used for traffic calculations. PCU conversion factors allow different types of vehicles, such as cars, buses and two-wheelers, to be represented using a common measure when estimating road capacity and congestion.
Arikutharam said the DPRs and IIT-Bombay study rely on conversion factors dating from the 1990s. He pointed out that these values give two-wheelers a higher conversion factor than newer recommendations issued under Indian Roads Congress guidelines.
According to his assessment, this could result in the congestion contribution attributed to two-wheelers being overstated by approximately 30%.
Missing Origin-Destination Data
The IIT-Bombay report itself acknowledges that the two DPRs do not contain an origin-destination survey. Such a survey tracks where journeys begin and end and is used to understand how people are likely to distribute themselves across different routes.
Arikutharam said the absence of this information is significant because it becomes difficult to determine how traffic would actually use the tunnel and elevated corridor without knowing travellers’ destinations.
He also said the projections did not take into account the possible influence of a metro line and the proposed long tunnel.
Study Recommends Wider Gap Between Tunnel And Elevated Road
The IIT-Bombay assessment has proposed a change to the spacing between the elevated corridor and the tunnel. It recommends increasing the distance between the two structures from 80 metres to 250 metres, with the aim of allowing traffic to move more efficiently.
Arikutharam said implementing this recommendation could mean modifying aspects of the existing project design.
Why Did BDA Commission The Study?
The BDA has said the additional assessment was commissioned in response to the controversy surrounding the short tunnel proposal. A senior BDA official told The Times of India that the authority wanted an independent institutional assessment after the project faced strong public criticism.
The official said the IIT-Bombay study concluded that both the tunnel and elevated corridor would be required to cater to future traffic demand and described the findings as supportive of the proposal.
The BDA has stated that construction of the short tunnel is expected to be completed by the end of January 2028.
Earlier IISc Assessment Had Raised Different Concerns
The latest questions come after an earlier assessment by the IISc Sustainable Transportation Lab, led by Prof Ashish Verma, examined the likely traffic consequences of the tunnel.
That study found that while the tunnel could ease congestion at Hebbal Junction, traffic pressure could remain significant around its entry and exit points. Potential bottlenecks were identified near the Veterinary College and Esteem Mall, with the possibility of queues extending back towards neighbouring junctions.
The IISc assessment also considered issues relating to flooding and the structural implications of construction near Hebbal Lake.
Separately, the Karnataka High Court has sought information from the state government on whether the proposed tunnel could affect the lake’s inflow, outflow or underground water movement.
The project has also attracted objections from citizens over the proposed use of lake land and the cutting of trees.
Debate Now Centres On WhatThe Traffic Models Capture
With construction already in progress, the debate around the Hebbal short tunnel is increasingly focused on the assumptions and information underpinning the traffic studies.
The BDA maintains that the IIT-Bombay assessment supports the need for the tunnel and elevated corridor, while experts reviewing the study have questioned the age of the traffic data, the scenarios modelled, the absence of an origin-destination survey and the treatment of surrounding road networks.
The differing assessments leave the project’s traffic impact as a key issue as Bengaluru moves ahead with the proposed Hebbal infrastructure.
Quick Answers
Ask News18Transportation experts like Prof Ashish Verma and Satyajit Arikutharam have questioned the IIT-Bombay assessment’s reliance on older traffic data, modeling approaches, outdated Passenger Car Unit conversion factors, and the lack of an origin-destination survey.
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September 29, 2026, 13:45 IST
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