Analysis of Class 175 Fleet Reliability

 Analysis of Class 175 Fleet Reliability and Service Reintroduction

This briefing document examines the historical reliability challenges and the current reintroduction strategy for the Class 175 Coradia diesel multiple unit (DMU) fleet. It details the technical failures experienced under previous operators and the measures currently being implemented by Great Western Railway (GWR) and Alstom to ensure operational stability.

Technical Specifications: Class 175 Coradia

Built between 1999 and 2001 by Alstom at Washwood Heath, Birmingham, the Class 175 fleet consists of 27 trainsets owned by Angel Trains.

Specification	Class 175/0 (2-car)	Class 175/1 (3-car)
Format	DMSL-DMSL	DMSL-MSL-DMSL
Service Weight	49.75 tonnes (per car)	146.761 tonnes (total)
Length	23.713 m (Driving vehicle)	70.45 m (Total unit)
Width	2.73 m	2.73 m
Seating Capacity	134	206
Maximum Speed	100 mph	100 mph
Body Construction	Steel	Steel

Historical Reliability Issues (2000–2024)

Since entering service in May 2000, the Class 175 fleet has been characterized by significant mechanical and electronic failures. These issues persisted through tenures with First North Western (FNW), Arriva Trains Wales (ATW), and Transport for Wales.

Mechanical and Structural Failures

Early operations were marred by fundamental hardware deficiencies that required extensive remedial work:

• Bogie Defects: The fleet required significant modifications to its bogies to meet safety and performance standards.
• Braking Systems: Problems with the original braking systems necessitated engineering interventions to improve stopping performance and reliability.
• Engine Efficiency: The units are described as replacing "heritage" DMUs but eventually became viewed as less efficient compared to modern standards, contributing to GWR's decision to utilize them only as a "rejuvenation" measure for regional services.

Passenger Information System (PIS) Malfunctions

A recurring issue involved the automated announcement and display systems, which were often non-functional:

• System Errors: Internal problems with the Alstom-fitted PIS led Arriva Trains Wales to cease using the system entirely upon acquiring the fleet.
• Display Issues: Because the PIS was disabled, the external LED destination displays on the front and rear of the trains remained unlit, causing passenger confusion.
• 2007 Reprogramming: The system eventually required a total overhaul in 2007 to introduce new routes, Welsh spellings, and audio chimes to signal announcements.

Great Western Railway (GWR) Reintroduction Strategy

In March 2024, GWR signed a lease for 26 Class 175 units to bolster services in South West England, specifically targeting routes between Exeter St Davids, Penzance, Barnstaple, and Okehampton. To address the fleet's historical reputation for unreliability, a £75 million Technical Support and Spares Supply Agreement (TSSSA) was established.

Predictive Maintenance via Alstom HealthHub

The primary strategy for improving reliability under GWR is the implementation of the HealthHub digital solution. This represents the first time a GWR fleet has utilized condition-based and predictive maintenance technology.

• Real-Time Data Analysis: Each train transmits data on more than 200 parameters every 30 seconds.
• Monitored Metrics: Parameters include train speed, internal carriage temperature, and GPS coordinates.
• Incident Prevention: The system is designed to alert maintenance teams to anomalies in real-time, allowing for repairs before mechanical failures impact passenger service.

Operational Support and Infrastructure

• Maintenance Hub: Ongoing support is centralized at GWR’s Laira depot in Plymouth.
• Specialized Staffing: The contract supports 15 dedicated roles, including material planners and engineers, specifically to manage the Class 175 reintroduction.
• Fleet Modernization: GWR intends to use these units to facilitate the removal of its "oldest and least efficient" diesel trains, aiming for a tangible boost in regional punctuality.

Conclusions on Fleet Status

The Class 175 fleet has transitioned from a troubled introduction in the early 2000s—defined by bogie, brake, and electronic failures—to a highly monitored regional asset. The success of the current reintroduction depends heavily on the HealthHub digital suite's ability to shift maintenance from a reactive to a predictive model. While remedial work in the mid-2000s improved core mechanics, the £75 million investment by GWR and Alstom underscores the ongoing high cost of maintaining the operational integrity of these Alstom Coradia units.

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