Rail and airline operators want to provide their best service offer in a form that meets the needs of passengers across a spectrum of different routes and journey times. People come in all shapes and sizes with differing needs and preferences. What is perceived as soft and welcoming by one person may be considered lacking in form and support by another. This diverse range of use cases and personal preferences poses a multi-factorial problem when designing mass transit seating for comfort.
This ‘comfort conundrum’ is best tackled by a development team that embraces human factors, engineering, and creative design – supported by the ability to dynamically build, test and modify practical rigs. While no one element dictates that a seat will be comfortable, some key features can make a difference. It is the role of the designer to strike the right balance between these to achieve an optimal solution that will satisfy the largest number of people.
Comfort is a vital part of seat design and a key area with scope for innovation and differentiation. It is a topic that is currently experiencing renewed attention. The recent UK Rail Industry Guidance Note (GMGN2696; an updated version of RSSB report T1140) refers to Commitment 41 in the Williams-Shapps Plan for Rail, published in May 2021. This report acknowledges that, with an emphasis on accommodating more passengers, the designs of some new trains have compromised passenger comfort. The Guidance Note is clear that this balance needs redressing.
This reminder is timely, since in the post-Covid world, there has been a change in commuting patterns. Many people are now actively avoiding the traditional ‘rush hours’, opening up the possibility of fewer seats and more space in our public transport vehicles.
Perceived seat comfort
The challenges of designing for perceived seat comfort are summarised in the diagram below that breaks down the influencing factors into four distinct areas: the seat (Product), the journey type (Activity), the passengers (People), and the space (Environment). Our primary focus in this article is to consider the blue sector of this diagram (Product), which addresses the practical considerations directly within the control of the seat designer. We use the factors in the outer ring of this sector as sub-headings to highlight the key seat design issues, while acknowledging the impact of the other three sectors on our design decisions.
Before designing the detail of a seat, it is imperative to define the seat format. The seat format will be heavily informed by the journey type (the red Activity sector). The specification of the seat format will differ between very short sitting durations, such as those on metro services, often with frequent stops; medium length journeys on regional trains; and the extended sitting durations experienced on intercity trains.
Here we have chosen to focus on a generic passenger seat aligned with the direction of travel, facing forward or rearwards. However, the insights are generally transferable across all formats of transport seating.
Size and shape
The size and shape of the of the seat will be determined primarily by three factors:
• The passengers (the yellow People sector).
• The demands on space (the green Environment sector).
• The format of seating.
However, Guidance Note GMGN2696 simplifies the designer’s task in this respect by offering clear guidance on seat dimensions, while in the EU, a EuroSpec document has been released that provides a very similar approach and level of detail.
Materials and finishes
The materials that make up the various elements of a seat interact in a highly complex fashion to deliver a unique seating experience. When they sit down, most people appreciate a small amount of give from their seats. It is nice to feel the seat cushion beneath us absorb the impact, to respond in a welcoming fashion to the act of sitting down. However, if the seat cushion is too soft, we sink in too far and can end up in an uncomfortable postural position, particularly if we are sitting for long periods. Space and weight can also be major issues with soft seats. If they are not sufficiently deep, there is the risk of ‘bottoming out’ and hitting the rigid seat structure beneath the cushion.
Just like high-end mattresses, some of the most comfortable seating experiences are both soft and firm at the same time. They include a more compliant section integrated together with a stiffer supportive element. These soft and supportive elements can both be within the cushion itself and may be as simple as two layers of different density foam.
Alternatively, they may include a complex mix of materials, including springs, foams and meshes.
The seat frame itself can contribute to this complex blend of softness and support. It may include some form of spring or air suspension. Strapping or webbing can be incorporated. Or the frame itself may bend or deform elastically.
Seat adjustability adds a further level of complexity to the seat design compared with fixed solutions. As one element, for example the seat back angle, is adjusted, other elements, such as the seat cushion angle, should also be changed. If the seat back angle is adjusted in isolation, the occupant will become uncomfortable and is also likely to slide forward on the seat cushion. In some seats, such as high-end automotive seats, the occupant can control multiple elements independently to achieve their preferred combination of positions and geometries. In other cases, like some first class rail seats, multiple elements are linked and adjust together to maintain a preferred posture group.
To further complicate things, the optimum softness or firmness of the seat is not a fixed requirement. The ideal solution will vary depending on the way the seat is used, as well as who is using it (their size and shape; their weight and BMI) and the stage of their journey. It is also likely to change as the seat is adjusted, so that the optimal level of support will be different in an upright position compared to a more reclined posture. When we sit upright to eat or work, a notable proportion of our weight is in contact with the seat cushion. As we recline the seat, weight is transferred from the seat cushion to the seatback. As the mass on the cushion reduces, it is desirable to change the cushion’s firmness.
It is possible to envisage a seating system in which such firmness adjustment is achieved automatically to suit recline angles and other sensed variables. These could include occupant mass, the activities being conducted (is the infotainment system playing a movie, or is food being served?) or the duration of the journey completed. Alternatively, the option for manual adjustment could be provided – allowing passengers to dial the seat stiffness up or down to suit their current requirements. Such a system has the potential to transform a passenger’s experience of comfort when travelling.
Active comfort system
Inspired by this vision of active comfort control, DCA has been exploring ways that we might provide passengers with the ability to interactively change the physical characteristics of their seat cushion to control the firmness of the cushion support. Making this an adjustable feature allows each person to adjust the seat to suit their physical needs, and to do so dynamically as these needs change through their journey.
The resulting patent pending ‘Active Comfort System’ controls the cushion firmness experienced by the passenger via a variable tension fabric membrane positioned between two distinct cushioning layers, each designed to offer a different level of compliance, using a combination of springs, foam or non-woven materials. The tensioning system may be manually actuated or automated to adjust the tension in the membrane, thereby varying the degree to which the lower cushioning layer contributes to the seat cushion softness. Using the interaction of the tension membrane with this dual cushioning setup, each person can set the cushion firmness and compliance to suit their instantaneous preference.
We believe that the ‘Active Comfort System’ goes a long way to solving the comfort conundrum. One of the many advantages of active seat comfort control is the ability to adjust the feel of the seat over time. At the start of a journey, the seat cushion can be soft and pliable. Then, as the journey progresses and perhaps tiredness sets in, the seat cushion can be made firmer and more supportive. Placing this level of control into the hands of the user means that we can cater for their individual and changing requirements, both physical and psychological.
We presented a proof of principle demonstrator of the system at the Rail Interiors Show in Prague in October 2023 to a very positive reception and it has been short listed for the Technological Innovation of the Year Award at the RedCabin Railway Interior Innovation Summit hosted by OEBB in Vienna.