IRC 106:1990 is the Indian Standard (IRC) for guidelines for capacity of urban roads in plain areas. IRC 106:1990 provides capacity analysis methodology for Indian urban roads — arterials, sub-arterials, collectors, and local streets. Capacity is the maximum sustainable flow of vehicles per unit time; Level of Service (LOS) categorizes quality of flow from LOS A (free flow, v/c < 0.30) to LOS F (breakdown, v/c > 1.00). Urban target is typically LOS C (v/c 0.60-0.75). Base capacity ideal: 1800 PCU/hr per lane of 3.5 m width; urban practical 1200-1500 PCU/hr due to adjustments for narrower lanes, lateral obstructions, bus stops, cross-traffic. PHF (Peak Hour Factor) typical 0.80-0.90 for urban India — means significant peaking requiring over-design. Intersection capacity (signalized and un-signalized) typically the limiting factor in urban arterial throughput — not mid-block capacity. Amendment No. 1 (2015) added microscopic simulation methods (VISSIM, SIMTRAFFIC) for complex urban networks. Amendment No. 2 (2022) updated PCU values reflecting changed Indian vehicle mix (more 2W and cars, fewer 3W). Urban road capacity analysis is critical for: road widening decisions, traffic signal design, intersection improvements, bus lane justification, and sustainable urban transport planning.
Specifies methodology for calculation of capacity of urban roads, arterials, and streets in plain areas — including level of service analysis, saturation flow, effective width factor, and peak hour factor for traffic design.
- Status
- Current
- Usage level
- Essential
- Domain
- Transportation — Traffic Engineering
- Type
- Guidelines
- Amendments
- Amendment No. 1 (2015) — microscopic simulation methods (VISSIM, SIMTRAFFIC); Amendment No. 2 (2022) — updated PCU for changed vehicle mix (more 2W/cars)
Also on InfraLens for IRC 106
Practical Notes
! LOS C (v/c 0.60-0.75) is typical urban design target. Design for LOS D in peaks; LOS E+ is congested and problematic. Major Indian cities often operate at LOS E-F during peaks.
! Mid-block capacity rarely limits urban arterials — signalized intersections are the bottleneck. Focus on intersection capacity for meaningful urban analysis.
! Peak Hour Factor (PHF) 0.80-0.90 means peak 15 minutes has 1.1-1.25× average hour volume. Design for peak, not average.
! Base capacity 1800 PCU/hr per lane is IDEAL. Urban practical: 1200-1500 PCU/hr after all adjustments. Indian conditions: lower due to heterogeneous traffic (mix of 2W, 3W, cars, trucks, buses).
! Lane width 3.5 m is standard. Narrower (3.0 m) causes 3-6% capacity reduction. Wider (4.0 m) marginal gain. Very narrow (2.75 m) typical on older roads — major capacity loss.
! Heterogeneous traffic: Indian roads have 2W (0.5 PCU), 3W (0.75 PCU), cars (1.0), buses (2.5), trucks (3.0), MAVs (4.5) all mixed. Total PCU count differs from vehicle count.
! 2W effect on capacity: high 2W proportion reduces effective capacity because 2Ws occupy less space but disturb lane discipline. Aggregate PCU analysis captures this.
! Intersection capacity: limited by green time × saturation flow. Signalized intersection typical 1800 vph per approach; un-signalized 300-900 vph.
! Signal coordination: 10-20% capacity gain on arterial via progressive green timing. Cost ₹5-15 lakh per corridor for coordination system.
! Bus bays: dedicated lane for bus stopping. Prevents bus-induced capacity loss (20-30% per stop). Cost ₹50 lakh-2 crore per bus bay.
! Cycle / pedestrian obstruction: 10-30% capacity reduction. Segregated cycle tracks (per IRC 11) mitigate this.
! Parking on urban roads: 20-40% lane capacity reduction if vehicles park on edge. Designated parking off-road preferred; parking prohibited on arterials.
! Vehicle lane discipline: Indian drivers often straddle lanes, overtake from wrong side. Reduces effective capacity below theoretical. Enforcement improves compliance.
! Micro-simulation (VISSIM, SIMTRAFFIC): models individual vehicle behavior for complex interactions. Identifies bottlenecks precisely. Cost ₹2-20 lakh per model.
! Adaptive signals (SCATS, SCOOT): real-time optimization based on traffic flow. 10-30% capacity gain over fixed timing. Investment ₹5-15 lakh per intersection.
! Urban capacity enhancement strategies: signal coordination + bus bays + signal timing + adaptive signals + micro-simulation-based design. Cumulative 30-60% capacity gain.
! Road widening as capacity solution: linear gain with lane addition but high cost and land requirement. Typically not preferred over other interventions in dense urban areas.
! Dedicated bus lanes: controversial due to perceived capacity loss but actually increases corridor capacity (buses carry more passengers per lane than cars). Delhi BRT and Mumbai BRTS examples.
! Weather impact on urban capacity: monsoon reduces capacity 20-30% due to wet pavement, reduced visibility, flooding. Design assumptions often ignore this.
! For Smart Cities Mission: real-time capacity management via ITS (adaptive signals, VMS, CCTV) gives 15-30% effective capacity gain. Much cheaper than road widening.