Why in news?

The Centre has approved adding a third and fourth rail line on the 32 km Badlapur–Karjat stretch in Maharashtra, extending the Mumbai Suburban Corridor and strengthening a key segment of the 1,238-km Mumbai–Chennai High Density Network (HDN).

This corridor—one of India’s most saturated—links Mumbai to Chennai via Pune, Solapur, Guntakal and Arakkonam.

The decision is part of Indian Railways’ broader plan to decongest all seven High Density Network corridors, which make up just 16% of the total network but carry 41% of all rail traffic.

As passenger and freight demand surges, expanding and improving the HDN has become crucial to ensuring smoother, more efficient railway operations.

What’s in Today’s Article?

• About High Density Network (HDN)
• India’s Seven High Density Rail Corridors: Nationwide Coverage
• Future Congestion Projections
• Line Expansion: The Core Strategy for Decongestion

About High Density Network (HDN)

• The HDN comprises passenger–freight corridors where train operations are running beyond optimal capacity, causing congestion, delays, and reduced efficiency.
• Out of 69,181 route-km of Indian Railways, the HDN accounts for 11,051 route-km (15.97%).
• These highly saturated corridors are divided into 237 sections, each with varying levels of utilisation.
• HDN Is Overloaded
  • A rail network ideally functions at 70–80% capacity for smooth operations.
  • The HDN far exceeds this:
    • Only 4.60% of HDN routes operate below 80% capacity
    • 18.89% operate at 80–100%
    • 32.75% at 100–120%
    • 29.53% at 120–150%
    • 14.11% run at over 150% capacity
  • This means 95% of the HDN runs above the optimal threshold, many well beyond designed limits.
  • A majority of HDN sections operate at stress levels where delays and bottlenecks are unavoidable.
• An Example: The Overburdened Karjat–Lonavala Section
  • On the 28-km Karjat–Lonavala stretch (part of the Mumbai–Chennai HDN):
    • 67 trains run each way per day
    • Maximum capacity: 40 trains
  • This results in 167% capacity utilisation — far above ideal levels.
• How HDN Compares With the Overall Indian Railways Network?
  • According to the National Rail Plan (2051 vision document):
    • 45% of the entire Indian Railways network operates below 70% utilisation
    • 29% operates at 70–100%
    • 25% runs at 100–150%
    • Only 1% exceeds 150% utilisation
  • In contrast, the HDN is severely overloaded, highlighting why expansion and decongestion of these seven corridors is a top priority.

India’s Seven High Density Rail Corridors: Nationwide Coverage

• The High Density Network (HDN) spans all four regions of India, consisting of seven highly saturated corridors:
  • Howrah–Delhi (1,422 km) - Only 31.34 km (just two sections) operate below 80% capacity. The entire remaining corridor is heavily saturated.
  • Howrah–Mumbai (2,039 km) - Only 85.2 km operates below 80% capacity. Most of this Golden Diagonal corridor faces high congestion due to intensive freight and passenger load.
  • Mumbai–Delhi (1,322 km) - One of the only two HDNs without any section exceeding 150% utilisation. The Western Dedicated Freight Corridor (WDFC) runs parallel, absorbing freight pressure.
  • Delhi–Guwahati (1,876 km) - A staggering 96% of the corridor operates above 80% utilisation. Faces both heavy passenger movement and significant freight demand.
  • Delhi–Chennai (2,037 km) - Nearly 52% of the corridor is running at 120–150% capacity, one of the highest saturation ratios in the network.
  • Howrah–Chennai (1,117 km) - 50% of this corridor operates at 120–150% utilisation, indicating tight capacity.
  • Mumbai–Chennai Corridor - Almost 90% of the corridor sees utilisation in the 80–120% range. This corridor remains extremely busy, with several sections nearing saturation.

Future Congestion Projections

• The National Rail Plan warns that without major upgrades, HDN congestion will rise dramatically:
  • By 2051, no HDN section will operate below 100% capacity utilisation.
  • 92% of the HDN will exceed 150% utilisation, far beyond safe or efficient levels.
• Near-Term Outlook: Heavy Overload by 2031
  • By 2031, the HDN is projected to be severely overstretched:
    • 50% of HDN will operate above 150% utilisation
    • 39% between 100–150%
    • Only 9% will remain within 70–100% capacity
  • This indicates that demand growth is outpacing infrastructure expansion.

Line Expansion: The Core Strategy for Decongestion

• While multiple operational reforms help improve train movement, line expansion—doubling, tripling, quadrupling, and even penta/hexa lining—is the most critical decongestion measure.
• Recent Progress in Line Expansion
  • Indian Railways has aggressively expanded capacity:
    • 1,983 km completed in 2021–22
    • 3,185.5 km in 2022–23
    • 2,244 km in 2023–24
    • 2,900+ km in 2024–25
  • This is helping, but far more expansion is needed given HDN congestion levels.
• Role of Dedicated Freight Corridors (DFCs)
  • The Eastern DFC (fully operational) and Western DFC (96.4% complete) are expected to divert freight traffic away from HDN, freeing capacity for passenger trains.
  • This is one of the most impactful steps in reducing HDN load.