With the introduction of Class 450 Desiro trains on the Portsmouth line services, South West Trains has received criticism from some passengers on the basis that the seating layout is uncomfortable and presents a potential risk to health including, but not limited to, the occurrence of back pain and deep vein thrombosis.

In response to this, South West Trains commissioned Interfleet Technology Ltd. to undertake an independent assessment of the seating design and layout and to benchmark it against that of comparable classes, together with a review of existing evidence and research relating to the link between seating design and health.

The review used existing appropriate anthropometric data based on an estimated male/female ratio of 90:10, which is believed to be more representative of the commuter population than the traditional 50:50 ratio.

The seating on Class 450 trains is manufactured by Grammer, and is in use on several other vehicles on similar types and lengths of route. The seating is within the RVAR specifications and falls within the general best practice set out for the provision of seating for a number of different applications, not just trains.

With increasing passenger numbers, there is a trend towards higher seating capacity on regional routes, commonly including the adoption of 3+2 seating in standard class. This allows more passengers to be seated, with fewer being required to stand, whilst still enabling trains to be designed within the limitation of the infrastructure on which they run.

Space constraints in the carriage, together with a requirement to keep a suitable aisle width make ideal seats impractical. 3+2 seating is a compromise based on the current carriage width constraints.

A seat that is judged to be “comfortable” may lead to back pain in the long term. Conversely, a seat that is judged “uncomfortable” may not be causing physiological damage.

Summary of findings

The review indicated that the risk of travel related DVT is negligible without the existence of predisposing risk factors in the individual. Furthermore, no studies identified the occurrence of DVT on journeys of the length of those taken on the Waterloo – Portsmouth route.

As part of the study the issue of “whole body vibration” (WBV) was explored. There is some evidence to suggest that WBV may be a contributory factor in the development of back pain. The level of whole body vibration experienced is the result of seating design, vehicle design and track quality. There are no U.K. rail industry standards for acceptable level of exposure, but guidance issued by RSSB (Rail Safety and Standards Board) in response to European Union Directive 2002/44/EC suggests that the level of exposure to staff working on trains is unlikely to reach levels requiring action. Given the level of exposure to passengers is very unlikely to be greater than that of employees who work on trains, the likelihood of WBV causing medical harm to passengers is considered to be minimal.

As with all of the vehicles surveyed there are some elements of the class 450 design that limit the percentage of the population that are physically accommodated.

The literature review looked at current best practice for provision of seating for a number of different applications not just trains. The following table summarises the results for the class 450 when compared to the results of the literature review.


Best practice	How 450 compares
Seat height should not be greater than the length of the lower leg, nor should it be too low. However a seat that is too low is preferable to one that is too high.	The class 450 seat height is comparable to other vehicles surveyed in terms of representing a compromise between the needs of the smaller and larger users.
Seat depth should be less than the distance from the back of the buttocks to behind the knee (popliteal area).	The class 450 and 360 seat depth is larger than most vehicle classes, whilst still resulting in only 4% of the population not being accommodated. As such it supports more of the leg whilst still accommodating more than 95% of the population.
Seat width should be comparable with body width	The seat width of the class 450 is comparable to that on other vehicles surveyed.
Seat should have a rounded front edge.	All of the seats surveyed had a rounded front edge.
Seat should be appropriately contoured	All of the seats surveyed had slight contouring.
Seat cushioning should not be too soft.	All of the seats surveyed had slight contouring.
Seat should be tilted by 4-10 degrees	The tilt on the 450 is 7.5 degrees and therefore falls in the mid range of design parameters.
Smooth low friction seat covers should be avoided	None of the rail vehicle seats surveyed had a low friction seat covering.
Back tilt should be 10-15 degrees from the vertical	The seat back tilt is 9.9 degrees and therefore falls just outside the recommended best practice. The angle therefore between the seat base and back does result in a more upright sitting position in the class 450 than on some other designs. There is no evidence to suggest that this in itself is harmful, but comfort may be affected by the posture adopted and secondary tasks being undertaken by the passenger.
Seat should not push the shoulders and head forwards	None of the seats surveyed push the head and neck forward.
Backrest should support the lumbar region.	All of the seats provide a degree of lumbar support.
Arm rests should be considered.	None of the rail vehicles surveyed provided arm rests in standard class, except where seats were in a declassified first class area.

Best practice	How 450 compares
Feet should be supported	Seat height is comparable to other vehicles surveyed. None of the vehicles surveyed provide solutions to the trade off between designing for the larger and smaller users.
Knee clearance should be determined by buttock-knee length.	Knee clearance largely fell into two ranges, of which the class 450 is in the better group.
Foot room should be provided underneath the seat.	All of the vehicles surveyed had occasional limitations to foot space, but were otherwise unrestricted.

Conclusion

The independent assessment confirms that there is nothing ergonomically wrong with the Class 450 seating and that it meets current best practice for the provision of seating, in many areas at the better end of the scale.

When comparing seat width to hip breadth, the assessment identified that approximately 84% of the population would be accommodated by the Class 450 seat pan design. However, it does recognise that there are some issues with seat width, and based on the available anthropometric data that when all seats are occupied, based on the 90:10 population, 59% of the population will exceed their seating envelope with their elbows. This however is a comfort issue and not a health risk.

As part of the assessment exercise 19 other Train Operators were contacted and asked if they had any seating health issues reported. No instances of DVT or back pain were found to have been reported by Train Operators operating 3+2 seating on comparable routes to South West Trains.

It is therefore reasonable to conclude that the criticism received is due more to comparison between the class 444 and 450 than the actual design of the class 450 seating.