Putting rollingstock glare in the spotlight
While supporting the design of the Hitachi Class 800 train (also known as the IEP or, in the case of LNER, Azuma), we developed and published a new method for assessing glare within train cabs. Ten years later, we discuss how we have adapted this method to work across a diverse range of train cabs at various stages of the design process.
Similar to automobiles, glare can significantly affect a driver’s performance and overall experience. This glare can originate from illuminated objects inside the cab, such as displays, controls and lights, as well as from external sources like the sun, other trains and external lighting. Additionally, glare can be caused by reflections from these light sources, both inside and outside the cab.
The design of the cab plays a significant role in the likelihood of glare becoming an issue. Several key factors influence how glare is perceived and its impact on visibility within the cab:
- The size and location of the windows.
- The geometry of the cab desk, including the angles of the panels and whether it has cowling.
- The positioning and angles of light sources, such as displays, controls and lights.
- The colours, materials, and finishes (CMF) of the cab interior, which affect its light reflection.
- The presence and positioning of blinds.
- The treatments applied to the windows.
The factors above are listed in approximate order of how difficult they would be to modify in later stages of the project. For instance, adding a film to tint the side windows is a relatively simple change compared to altering the size and position of the windows, which would probably necessitate revisiting crash-worthiness calculations. Therefore, it is crucial to understand how glare will affect the cab’s design as early as possible in the design process.
Our method significantly enhances assessment rigour. More importantly, it provides crucial insights early in the design phase, enabling cost-effective modifications without disrupting project timelines
How the method works
Several factors influence glare, including the intensity and location of the light source, ambient light conditions, atmospheric conditions, and the characteristics of the driver’s eyes. Due to the multiple factors involved, it is impractical to physically simulate and assess every possible glare condition. Therefore, the method adopted has been developed as a practical approach to provide indicative information about the cab design’s likely glare performance.
The assessment is divided into two stages to evaluate:
- Internal light sources
- External light sources
To evaluate internal light sources, it is essential to eliminate all external light from the cab. The easiest way to achieve this is by attaching blackout fabric to each window outside the train. Once the cab is completely dark, the internal light sources can be turned on in a controlled manner, allowing each one to be assessed individually.
The assessment process is both structured and subjective. It requires the assessor to identify any sources of glare and rate their severity using a nine-point Likert scale (the De Boer rating scale). If glare is identified, potential mitigations, such as masking light sources or repositioning them in different locations, should be explored.
The assessment of external light sources follows a similar procedure. The blackout fabric is removed from the windows, and a repositionable light source is set up on a boom. This light source can be moved around the train and aligned with predefined points on the windows. For each position of the light source, a subjective assessment of glare is conducted. If glare is detected, it is noted whether it is direct glare or reflective. The effectiveness of potential mitigations, such as lowering the sunblind, is also explored and recorded, as well as temporarily trialling design options such as the addition of cowlings to the desk or the adjustment of screen locations and/or angles.
How we have applied it
To date, we have implemented this approach across five different train cabs, including full-width intercity cabs and gangway cabs. The assessments were conducted at various stages, from early mock ups to production vehicles. While the assessment methodology was generally consistent across these trains, minor adjustments were made to accommodate different window shapes and sizes, particularly for gangway cabs.
To address challenges related to the subjectivity of the assessments, we often involved multiple assessors in our evaluations. These assessors were carefully selected to represent a range of ages and eye conditions, including those with and without spectacles. Additionally, where multiple assessors took part, they were encouraged to adopt their natural driving postures rather than the default centralised position typically used by a single assessor.
In most cases, the glare evaluations led to design changes in the rolling stock. However, the extent of these changes varied. The modifications included adjustments to desk panels to alter screen angles, changes to the design of the cowling around the cab desk, recessing lights, adjusting lighting angles, modifying interior colours, and applying films to the side windows. When appropriate, we repeated the assessments after making these modifications to ensure the changes achieved the desired outcomes.
Summary
The glare assessment approach outlined in this article was developed to address a critical gap in the field of rolling stock design. At the time of its inception, no formal methods existed for evaluating glare in this context. To bridge this gap, we established a rigorous, repeatable and practical assessment method, which was later published in Applied Ergonomics. Since then, it has been cited in several key rolling stock design documents, solidifying its impact on the industry.
As outlined in our original paper, this method was designed to be practical and effective in mitigating glare from internal and external light sources. Over the past decade, it has proven invaluable - not just for optimising design but also as a vital tool for demonstrating regulatory compliance.
While the approach has its limitations - such as the lamp representing the sun and the tests typically being conducted on clean, dry windscreens (rain, ice, or dirt may influence light scattering) - it remains a powerful component of a robust glare assessment process. When combined with dynamic testing, this method significantly enhances assessment rigour. More importantly, it provides crucial insights early in the design phase, enabling cost-effective modifications without disrupting project timelines.
The original article was published in Applied Ergonomics, in March 2015, available with this link:
