The Use of Invalid Carriages on Highways Regulations 1988 (SI 1988/2268) defines three classes of invalid carriages:
- Class 1 - not mechanically propelled
- Class 2 - mechanically propelled at no more than 4 mph
- Class 3 - mechanically propelled, capable of exceeding 4 mph but not exceeding 8 mph
Most of the differences are irrelevant to this discussion, this is a UK-only concept and, indeed, many users will not know what Class their powerchair or scooter is. Indeed, I wonder how many Class 3 users know that the law requires them to engage a speed limiter to hold their speed below 4 mph when operating on a footway (i.e. pavement) and that their chair must be registered with DVLA (though it does not have to display registration plates, be taxed or have third-party insurance). A rear-view mirror is compulsory on Class 3, but most Class 3 powerchair users take the mirror off because it gets in the way and does not give an especially useful rear view.
The 1988 Regulations originally set the maximum unladen mass as 113.4kg for Classes 1 and 2, and 150kg for Class 3. However, The Use of Invalid Carriages on Highways (Amendment) (England and Scotland) Regulations 2015 (SI 2015/59) raised the limit for all classes to 200kg when the usual user has a clinical, postural, hygienic, caring or nursing need for additional equipment. The 2015 amendment was primarily to allow for chairs with multi-axis powered seating systems or sit/stand systems, which can exceed 150kg - some chairs have lift, tilt, recline and powered footrests.
The nameplate on a wheelchair will typically contain the maximum user mass and the maximum total loaded mass, but it is very unlikely to contain the unladen mass of a particular chair. Most modern powerchairs are modular - the prescriber or user selects a base model, then the configuration for that particular chair. As modular chairs can be reconfigured after leaving the factory, the manufacturer will not show a nameplate unladen mass as it could be inaccurate. If you add powered lift to a chair that did not have it before, you are going to add a fair amount of mass to the chair for the lift mechanism and the actuator that drives it. Upgrading the batteries on a chair will also add a significant amount of mass - most chairs still use lead-based batteries (gel cells or AGM that are rated for deep discharge).
On top of all this, many users will not know their mass accurately, especially those whose mobility is most affected. It can be quite an ordeal to weigh someone who cannot transfer without being hoisted.
Most chair/user combinations are going to be under 300kg - most chairs are under 150kg and so are most users. However, I can think of one chair that is up to 180kg from the factory with a 160kg maximum user mass - and that is before you add on heavy accessories such as gel-filled pressure relief cushions. It would be better if PSVAR lifts and tiedown systems were rated at 350kg, but I appreciate this will increase costs whilst only making the vehicle accessible to a small number of additional users.
There will always be some who cannot fit on an accessible coach, especially bariatric users using heavy duty chairs, who are likely to be too heavy and too wide.