Bengaluru’s proposed Hebbal short tunnel is now facing a more consequential challenge than public opposition: questions over whether the traffic evidence used to support it is sufficiently current, transparent and comprehensive. A study commissioned by the Bangalore Development Authority (BDA) after criticism of the project has been questioned by IISc and city-based mobility experts over its data sources, modelling method and assessment of traffic benefits.
The August 2026 study, titled ‘Integrated Traffic Microsimulation Study – Bengaluru: Hebbal Flyover & Hebbal Short Tunnel’, was prepared by Prof Archak Mittal of IIT-Bombay for Rithwik Projects Private Limited. Its stated purpose was to assess the traffic effects of the proposed Hebbal short tunnel and the associated elevated corridor near Mehkri Circle.
The study’s significance lies in the role such models play in infrastructure decisions. A traffic simulation does not merely describe existing congestion. It is used to compare possible interventions, estimate future movement and establish whether a project is likely to deliver the benefits claimed for it. If its baseline data, assumptions or scenarios are incomplete, the resulting recommendation can become difficult to test independently.
The evidence dispute is centred first on the study’s traffic data. Prof Ashish Verma, Convener of the IISc Sustainable Transportation Lab, reviewed the IIT-Bombay study and said the traffic information had been sourced from the detailed project reports provided by the contractor. His review noted a significant difference between the speeds reported in the documents.
For 2027 peak-hour traffic in the base case, the IIT-Bombay model reported a speed of 13.74 kmph, while the DPR for the Hebbal Short Tunnel Project reported 4.29 kmph. The supplied report does not establish which figure is more accurate. But the gap matters because forecasts of project performance depend on the starting conditions against which future improvements are measured.
Verma also said the study did not report queue lengths before and after the proposed interventions and did not explain its methodology in sufficient detail. Average speed can indicate movement across a network, but queue length is central to understanding how congestion is experienced at junctions, ramps and bottlenecks. Without both measures, it becomes harder to assess whether a project reduces delays at the critical locations or simply shifts congestion elsewhere.
The proposed road geometry raises another question. According to Verma, the elevated corridor at Mehkri Circle does not include a ramp for vehicles travelling straight towards Windsor Manor. Vehicles turning from Mehkri Circle would therefore be able to use the flyover, while a substantial share of vehicles travelling straight would continue to depend on the existing underpass.
That design feature makes the project’s traffic impact dependent on more than the capacity of the tunnel or flyover itself. It requires an assessment of how different traffic movements are separated, which vehicles are diverted and what happens to those remaining on existing roads. Verma also questioned how the elevated corridor would integrate with a proposed east-west corridor between Yeshwanthpur and KR Puram. The study, he said, did not clearly explain how traffic would be managed after congestion was shifted or how the projects would work together.
This is the institutional problem behind the technical criticism. Bengaluru’s major road projects are not isolated structures. A tunnel, flyover, underpass or elevated corridor changes turning movements and traffic distribution across adjoining roads. The evaluation therefore has to cover the full network affected by the intervention, including environmental consequences of traffic shifts. Verma said those impacts also required assessment.
Former Directorate of Urban Land Transport chief technical adviser Satyajit Arikutharam identified gaps in both the original DPRs and the subsequent IIT-Bombay study. He said the study was expected to examine four scenarios: the base case, each of the two projects separately, and both projects together. Instead, he said, it assessed only the base case and the combined tunnel-and-elevated-corridor scenario.
That distinction is important because a combined scenario cannot show what each project contributes independently. If both projects are presented as a package, decision-makers and citizens cannot easily determine whether the tunnel is necessary without the elevated corridor, whether the elevated corridor delivers most of the benefit, or whether one intervention produces adverse effects that are concealed by the other.
The timing of the underlying data is another concern. Arikutharam said the traffic data in the DPRs predates the opening of an additional ramp at the Hebbal flyover in January 2026. Since the traffic situation changed after that ramp became operational, he argued that fresh surveys are needed before the need for the short tunnel can be established.
The issue is not simply that old data may produce an outdated snapshot. New road connections can alter route choices, turning patterns and the distribution of traffic at nearby junctions. A model based on conditions before the ramp opened may therefore be measuring a network that no longer exists in the same form. The supplied report does not include a newer origin-destination survey or other independent traffic count to resolve that uncertainty.
Arikutharam also criticised the use of 1990-era Passenger Car Unit conversion factors in the DPRs and the IIT-Bombay study. PCU values convert different vehicle types into a common measure for analysing road capacity. He said the older factors assign two-wheelers higher values than newer Indian Roads Congress guidelines recommend, potentially inflating the estimated congestion contribution of two-wheelers by around 30%.
The implication is that technical assumptions can influence the perceived scale of a problem before any physical construction begins. Bengaluru’s traffic mix includes large numbers of two-wheelers, so the conversion method used in a model can affect estimates of road pressure, capacity and project benefits. The supplied report does not state whether the study tested how its conclusions would change under updated conversion factors.
The absence of an origin-destination study is equally significant. Arikutharam said neither DPR recorded the different destinations of passengers. Such information is needed to determine whether traffic is likely to use one project, both projects or neither. Vehicles approaching Hebbal may not all be part of the same movement, and a facility designed for one direction or travel pattern cannot automatically solve congestion created by another.
The study also did not consider the impact of a metro line and the proposed long tunnel in its traffic projections, according to Arikutharam. The report does not provide details of the metro project or long tunnel, but their omission points to a broader coordination challenge: road capacity decisions are being evaluated within a transport system that may also include other major interventions.
The IIT-Bombay study has recommended increasing the distance between the elevated corridor and the tunnel from 80 metres to 250 metres for more efficient traffic movement. Arikutharam said this could require changes to the existing project design. This recommendation illustrates how a review intended to support implementation may itself create a new design requirement, with implications for land, construction planning and project coordination.
BDA’s position is that the study was commissioned precisely because the tunnel project had faced public criticism. A senior BDA official told The Times of India that there had been “negative publicity and outcry” over the short tunnel road, prompting the authority to seek a third-party institutional evaluation. The official said the study found that the tunnel and elevated corridor were “very much required” for future traffic and described the report as positive for the project.
The BDA official also said the short tunnel project would be completed by the end of January 2028. That proposed timeline gives the data dispute an immediate administrative consequence. If design changes, updated surveys or additional modelling are required, the authority will need to clarify how those steps fit within the project schedule.
The central question is therefore not whether Bengaluru needs better movement around Hebbal. The supplied evidence establishes that the area has been the subject of major traffic interventions, competing forecasts and public criticism. The more precise question is whether the available assessment demonstrates that the proposed tunnel is the right intervention, at the right scale, and in combination with the right surrounding projects.
At present, the report documents a clear disagreement rather than a settled technical conclusion. BDA regards the IIT-Bombay study as confirmation of the project’s necessity. IISc and mobility experts have questioned its baseline speeds, queue analysis, scenario selection, survey vintage, vehicle conversion factors, network integration and treatment of future transport projects. The next significant evidence will be any updated traffic surveys, a fuller disclosure of the modelling methodology and clarification of how the design recommendation and January 2028 completion target are to be reconciled.
