![\"Traffic](\"https:\/\/www.newsbeep.com\/au\/wp-content\/uploads\/2026\/10\/Barapullah_traffic_1790929447948_uGAZ_1790929462775_tT7e_ee9e0f9e-8b7e-49d3-b337-9592024445bc_Mo70.j.jpeg\" "\\"Traffic")
Traffic jam from Ashram to Lajpat Nagar after Barapullah Phase-III elevated corridor opened, in New Delhi. (Arvind Yadav\/HT Photo)<\/p>\nThe capital’s newest flyover needed two days to jam half of south Delhi.<\/p>\n
Traffic jam from Ashram to Lajpat Nagar after Barapullah Phase-III elevated corridor opened, in New Delhi. (Arvind Yadav\/HT Photo)<\/p>\n
Barapullah Phase-III, linking Mayur Vihar to the existing elevated corridor, opened to the public on Wednesday. By Thursday evening, HT reported, the 8 km drive from Safdarjung Hospital to Sarai Kale Khan was taking over an hour<\/a>, with queues across the Ring Road, Outer Ring Road, Mathura Road, the DND flyway and Bhairon Marg.<\/p>\n A Delhi Traffic Police drone survey found two faults<\/a>. At several points, two three-lane roads feed into one three-lane corridor. Where the new spur joins the existing flyover over Sundial Park, a lane ends abruptly. Construction, a college fest and a broken-down bus near Ashram made Thursday worse, but police and engineers pointed to the merges.<\/p>\n Traffic obeys physics that scientists have studied since the 1950s, and design manuals worldwide turn that physics into rules. Barapullah’s merges break several of them, and the science shows how predictable this jam was. A Public Works Department (PWD) official told HT the project’s planning studies were more than 20 years old.<\/p>\n Delhi\u2019s drivers then make a bad design worse. Lane-cutting and queue-jumping turn every merge into a scrum, and there are no policemen to enforce any discipline.<\/p>\n Also read: India’s road safety blind spot: Why road design goes without scrutiny<\/a><\/p>\n Cars flow like a liquid, up to a point<\/p>\n In 1955, British mathematicians James Lighthill and Gerald Whitham proposed treating traffic as a fluid; the American engineer Paul Richards reached a matching model independently a year later.<\/p>\n Their model makes a simple prediction. Add cars to an empty road and the number passing any point each hour rises, but after a critical density, drivers slow down to keep a safe gap, each car then spends longer on every stretch, and the hourly count falls until traffic crawls. Engineers plot this as an inverted U called the fundamental diagram. The top of the U marks a road’s capacity, the most cars it can move in an hour. Below that peak, any given flow can come from light traffic moving fast or heavy traffic crawling, and once a road tips past the top, every extra car cuts the number getting through.<\/p>\n Anyone stuck on a Delhi flyover has watched the next part play out. Cars moving freely reach the back of a queue and brake hard, then the car behind them brakes, then the one behind that. The tail of the queue creeps backwards up the road, car by car, even as the cars at its front inch forward. Physicists call this moving edge a shock wave, borrowing the term for the sharp jump in pressure that races through air from an explosion or a supersonic jet. In traffic the jump is from sparse, fast cars to packed, slow ones, and it travels against the direction of driving. That is how a merge over Sundial Park can stall cars kilometres away at Ashram.<\/p>\n The jam with no cause<\/p>\n The best demonstration of this physics was in 2008. Japanese physicists put 22 cars on a single-lane circular track 230 metres around and asked drivers to hold 30 km\/h with even gaps. There was no junction, closure or breakdown.<\/p>\n Within minutes, small differences in spacing grew until a cluster of cars stopped, and the jam rolled backwards around the ring “like a solitary wave”, the team wrote in the New Journal of Physics. “A bottleneck is only a trigger and not the essential origin of a traffic jam,” they concluded.<\/p>\n Drivers supply the instability. Each reacts a fraction of a second late and brakes a little harder than the car ahead, so a tap on the brakes at the front of a line becomes a stop twenty cars back. A road near capacity can jam with no trigger at all; give it a bottleneck and a jam is close to certain. A year later, an MIT-led team named these waves “jamitons” and showed their equations match those of detonation waves in explosives.<\/p>\n Three rules the merges break<\/p>\n Lane balance. The American AASHTO Green Book, a design reference used worldwide, says lanes after a merge should be “not less than the sum of all the lanes on the merging roadways less one”, and roads should drop “only one lane at a time”. Two three-lane roads need five lanes beyond the merge. Barapullah has three.<\/p>\n “The merger leads to a deadlock where six lanes try to merge into three,” Dinesh Kumar Gupta, additional commissioner of police (zone-II traffic), told HT.<\/p>\n Tapers. A lane that ends should narrow over a long stretch so drivers can find gaps at speed. An abrupt end forces everyone in it across within metres. Researchers Jorge Laval and Carlos Daganzo showed in 2006 that “lane-changing vehicles create voids in traffic streams, and that these voids reduce flow.” Each forced lane change sets off a fresh backward wave.<\/p>\n “Auxiliary lanes are created here but are poorly designed, which lead to sudden merging of vehicles,” said S Velmurugan, former chief scientist and head of traffic engineering and safety at the government’s Central Road Research Institute (CRRI).<\/p>\n Capacity drop. Once a queue forms, a bottleneck discharges fewer cars than it did just before, an effect traffic engineers call the capacity drop. A jammed merge feeds its own queue.<\/p>\n