Obviously TOC’s might order end - gangway door trains because they give flexibility regarding splitting/joining at junctions and increasing/decreasing length according to expected demand. I wonder how much the almost vertical surfaces increase fuel consumption compared to a streamlined train like a Class 800 when travelling at speed? Does the increased wind resistance cause problems at speed v a streamlined train? Do end gangway trains create a greater pressure wave in tunnels? Which type of front end is safer? Do drivers feel rather confined in the small cabs of end gangway trains and prefer those with cabs the width of the unit?
The answer to this question is…
…it depends!
The resistance of a train to motion may be described in mathematical terms by an equation which has three components - one is a fixed value, one varies directly with speed and the third varies with the square of the speed. This can be written as
Resistance = A + Bv + Cv^2
where A, B and C are constants and v is the speed.
Thus the aerodynamic drag is around half as much again at 125mph as it is at 100mph. This is why high speed trains need such high levels of installed power.
As a rule of thumb a longer nose (or streamlined front if you will) makes a noticeable difference to the drag above 80 to 90mph. A long nose has the benefit of reducing the pressure wave generated when entering or leaving tunnels at speed, look at some photographs of Japanese and some European very high speed trains.
It is also important to consider the shapes of the parts of the trains. Sharp corners generated vortices which add drag. BR found that even at speeds of around 60mph and above rounding off the corners of the cab fronts reduced drag from this source, that is it reduced the value of ‘C’ in the equation above. Doing this at the design stage costs nothing but is difficult afterwards. Most train design from the late 1960s onwards, as speeds rose, used rounded corners in one form of another .
This ‘rounding’ is also effective in the inter-coach gaps, and even more effective is reducing the inter-vehicle gap as much as possible - some Swiss trains have been very good at this.
The nose drag is but one component of the total aerodynamic drag. ‘Form drag’ caused by air passing the train also plays a significant role (this depends on the total area of the side, roof and bottom of the train and its ‘roughness’) as well as do eddies dragged along at the rear of a train travelling at speed. So the longer the train the less significant is the part played by the drag caused by the nose shape.
It is difficult to put a figure for improved fuel consumption on all this, but the attention paid to detail in the HST design, including totally enclosing the gubbins under the coaches in a smooth casing, meant that the drag came out significantly lower than originally calculated. This meant that with the same installed power 8 coach (and later 9 coach) trains could be operated with the same top speed (although with somewhat slower acceleration in the higher speed ranges) as the original 7 coach trains. So it does make a difference.
Regarding accident protection. All new trains, whatever the shape of the front, now have to meet the requirements of EN 15227,
Railway applications - Crashworthiness requirements for railway vehicle bodies.
I can’t answer the questions about how drivers feel!
