Why don't we have higher platforms?
To support the development of the Platform Train Interface (PTI) Strategy, the railway industry undertook a range of investigations into the current situation and potential changes. This included assessment of the actual positions of current platforms and train floors, and the potential benefits and adverse consequences of changing the ‘standard’ height.
The mainline rail network in Britain has more than 2500 stations and around 6000 platforms. In an ideal world all platforms would be on straight track and all would be at the standard position. In the real world many GB stations are historic buildings and the platforms were built by different companies to different standards. Research project T866 used industry data to investigate the range of curve radii through our platforms as well as the actual height and lateral offset of each platform relative to the track.
Looking at these diagrams, around 30% of the existing platforms conform to current height standards, and around 20% conform for lateral offset - only 7% conform to modern standards for both height and offset. Train vehicle footstep heights and positions are similarly variable due to their historical introduction, with earlier rolling stock often tailored to specific routes, whilst more modern stock is specified and designed to ‘go anywhere’, to meet the requirements of today’s railway.
Clearance is required between the train and the platform to allow for:
- Geometrical effects on curves (22% of platforms are on curves sharper than 1000 m radius)
- Suspension movement of the train
- Movement of the track during the maintenance cycle
- Passing trains and speeds (freight and non-stopping passenger trains)
- Track maintenance trains
- A safety margin
The majority of platforms on our network have to allow the passage of freight trains as well as access for track inspection and maintenance trains. So, to help understand whether the passenger environment would be better with higher platforms, analysis looked at the lateral offset needed to allow these trains to pass a range of different heights of platform. This analysis used conventional freight trains, curve radii down to 500m (which would exclude 7% of existing platforms), and reduced clearances. The results are illustrated below, showing that any increase in the platform height, to reduce the vertical step to the train, would require an increase to the lateral offset, increasing the gap to be crossed by passengers. Evidence to date suggests that a larger gap would be an increased risk for the majority of passengers and so the target height remains 915mm.
There are specific examples of higher platforms or sections of platforms, but these are generally in locations where the range of trains is limited and there is no freight traffic. These include Heathrow Express, parts of London Overground and the central section of Thameslink (London St.Pancras to Blackfriars and London Bridge).
An alternative approach could be to lower the vehicle floor on new trains, and this approach (combined with a sliding step) is being taken by Merseyrail for the new trains being procured by Merseytravel. They have the advantage of a fleet that is developed specifically for their use combined with infrastructure investment to decrease the platform variability. However, with minor vehicle / infrastructure changes it would be possible to use the trains elsewhere on the network if, as often happens, they were to be ‘cascaded’ onto other routes. It is a broad policy objective for new trains to be built so they can normally ‘go anywhere’ in due course. Deployable steps or bridging plates fitted to the train or the platform are also being considered in some areas.