Why do trains go 79 mph?

The 79 mph Speed Limit for Passenger Trains: A Shared Track Challenge

Passenger trains, while often a preferred mode of travel for their efficiency and environmental friendliness, frequently operate at a maximum speed of 79 mph (or less). This seemingly arbitrary limit stems from a crucial aspect of modern rail infrastructure: shared trackage with freight trains.

The reality of railway networks is that passenger and freight trains often share the same tracks. This shared use is economically essential, allowing for efficient use of existing infrastructure. However, different train types require different operating parameters. Freight trains, designed for hauling large quantities of goods over long distances, are typically optimized for lower speeds.

Crucially, the braking and acceleration characteristics of passenger trains and freight trains differ considerably. Passenger trains, carrying a high number of passengers and often travelling at a more consistent speed, must maintain a shorter stopping distance compared to freight trains. The maximum speed of passenger trains is therefore often determined by the ability of the infrastructure to safely accommodate the differing braking and acceleration profiles of both types of trains. If passenger trains were to operate at much higher speeds on shared tracks, the safety implications become significant, particularly during situations requiring rapid deceleration or emergency stops. The risk of collisions or near-misses with freight trains increases exponentially with increased passenger train speeds.

Going beyond 79 mph necessitates dedicated, separate tracks for passenger trains. This significantly increases the capital expenditure required to develop and maintain a railway network. Building entirely new lines, or upgrading existing tracks to accommodate faster passenger trains, is a complex and costly undertaking, often constrained by geographical factors and existing land use.

In conclusion, the 79 mph speed limit for passenger trains is not a mere arbitrary constraint. It’s a consequence of the complex interplay between passenger train needs and the practical realities of shared rail infrastructure with freight trains. The significant costs associated with dedicated tracks highlight the economic considerations that underpin the design and operation of modern railway systems.