Executive Summary & Background

Regional branch lines often face a critical economic dilemma: they rely on traditional voice train control, which offers a limited safety level, yet full-scale European Train Control System (ETCS) solutions involve capital expenditures that are far too expensive to justify. To bridge this operational and safety gap, Global Navigation Satellite System (GNSS) based control systems can be effectively utilized as a supplementary layer on top of basic voice operations.

The purpose of the paper is to help railway decision-makers operating small and medium-traffic lines improve their operating safety levels by comparing three primary scenarios:

• Scenario 1: Over-Voice-Based Control — The baseline system where all movement authorities, instructions, and safety verifications are conducted manually via voice communication, paper logs, and operational procedures without decision-support software or trackside equipment.

• Scenario 2: GNSS-Based Control with Brake Integration — An intermediate technological upgrade that introduces onboard GNSS tracking, automated geofencing, and a direct interface with the locomotive’s braking system to mitigate human errors in position reporting and overspeeding.

• Scenario 3: GNSS-Based Control Combined with Trackside Infrastructure — A comprehensive configuration overlaying satellite tracking with physical trackside elements (such as axle counters and point position detectors) to provide absolute ground-truth infrastructure verification and fail-safe command enforcement.

  Safety Measurement Methodology

  One important method for measuring a system’s safety level is identifying its safety-related functions and mapping their interdependencies using a Boolean logic fault tree. Once this model represents the operational scenario, its top event indicates the aggregate safety level by combining all Tolerable Hazardous Rate (THR) values.

  Tolerable Hazardous Rate (THR) and Risk Evaluation

  The CENELEC standard EN 50126 defines risk as a combination of the frequency of occurrence of a hazardous event and the consequence severity of those hazards.

  Frequency Categories: Ranging from Category A (Frequent, ) to Category F (Incredible, ).

• Severity Levels: Ranging from Catastrophic () to Insignificant ().

Risk evaluation combines these frequency and severity dimensions to establish resulting risk levels from Negligible to Intolerable.
Operational Hazardous Scenario Representation

Operational hazardous situations are grouped into three core subsystems:

• Train Driving Fault: Overspeed, wrong train position, corrupted communication, and unauthorized occupation.

• Dispatching Fault: Wrong authorized route, corrupted communication, and wrong temporary restriction.

• Track Information Fault: Corrupted communication and failure to obey or display switch position.

Economic Evaluation & Investment Methodology
To determine the optimal pathway for capital allocation, the paper defines an Investment Safety Return (ISR) metric that correlates risk reduction with capital expenditure (CAPEX) per kilometre: