**Track spacing and curvature issues**

I would like to extend the topic of track spacing and curvature to include modern European standards and recommendation which I believe apply to any other continent. My comments are based on handbook "Linie Kolejowe" ("Railroads") published in 2002 by Warsaw Polytechnic, Poland for students of faculty of Railway Transport Technology, year 3 and 4. As Poland is now part of European Union, it uses very similar if not exact criteria in designing rail roads what other European countries, such as Germany, Austria, Italy and some non-European countries like Japan. I believe these standards are not too far away from standards used nowadays in USA and Australia. This book proves that almost every route I got with TRS2006 or TC or from DS is NON-prototypical in general, not too mention in detail. Unfortunately I don't know if this book was translated into other languages and cannot refer an English version of it.

- Track spacing

It is not just so simple to state that the track spacing should be 3.5 m or 6 m or some other value. In a straight track the distance may be 3.5 m, but you need to add to it an extra length on curves; the smaller radius, the bigger distance between the tracks. One of the advantages of laying double track close to each other is that you save space when adding turnouts. If you plan to run trains with speed of 100 km/h in each direction, then you should use turnouts of angle of at least 1:18.5. The angle and the space between the track determines the minimum distance between two adjacent turnouts. If the distance between the tracks is 3.5 m then distance between two adjacent turnouts is 3.5 x 18.5 = 64.75 m. But if the distance between the tracks is 5.7 m (as required by some of TRAINZ bridges or other objects), then distance between two adjacent turnouts should be at least 105.5 m. So you need an extra 40 m just to add one turnout. The good news is that you need to do it only for the main track. For additional tracks you can lower speed to 60 or 40 km/h and increase turnout angle to 1:12 and 1:9 respectively. Then the distance will drop to 42 m and 68.4 m for 1:12 turnout and 31.5 m and 51.3 m for 1:9 turnout. Of course, if you want your route to emulate a real railway you should space additional tracks at least 6 m (for newly built lines recommendation is 6.5 m) and increase the gap between the turnouts accordingly. Similar principles apply to adding track side objects, platforms, etc. For simplicity I space tracks at around 5.7 m regardless whether it is the main line track or additional tracks on a station. This simplifies route design, speeds up implementation and eliminates the need for gantry which I found quite inflexible in terms of placing it over a track.

- Track curvature

In my opinion even the most spectacular and breath taking routes suffers from three major problems when considering realism and accuracy of track curvature:

1/ Imbalanced curves

2/ Spline spacing

3/ Insufficient (too small) curve radius to run trains within the speed limit.

Perhaps these problems are not a fault of route designer, but a general trend that TRAINZ emulate a model (carpet) railway like HO, TT, N, etc, rather than a real railway.

1/ Imbalance curves.

I use this term to describe the curves in which a singe spline shows completely different reading on each side. Say on left side I get reading of 500 m and on right side I get 50 m. This problem can by largely minimised by moving splines along the track until the reading is within 5-10% on both sides of the spline. More accurate spline positioning is not possible in TRAINZ without using some third-party tools, of which I would like to hear, if they exist. This makes difficult to design track for trains travelling with speed 400 km/h or higher where radius must be at least 8000 m, but slight touching of a spline changes the radius beyond acceptable error.

2/ Spline spacing.

I found that for some unknown reason if two adjacent splines on a curve are spaced too far away they are likely to cause a train to jitter, i.e.to move with an excessive and visible friction sideways. I think that the friction is caused, because the driver is not able to accurately plot direction of a train moving on a curve where nearby splines are too far away. This can be fixed by separating splines by no more than say 100 m (an exact value seems impossible to calculate). But it requires lots of extra work, so in my own routes I space splines at around 190 m. At this length there is no visible friction, unless you zoom in on undercarriage of cars or trucks.

3/ Curves radius.

A TT scale model train can run on a kitchen table with speed of 400 km/h on a curve of 50 m, which is hardly suitable for even roughest tram lines. So do TRAINZ! Isn't it wonderful? If you not happy with it, you can stick to the standards of European Union and calculate minimum radius of the curve from the formula:

R >= (Vmax / k) ^ 2

where R is the minimum radius of the curve in meters;

Vmax is the maximum speed of train;

k is a "magic number", equal to 4.6 or to 4.5 on some railways (Japan, Poland). The number is calculated from rather complex formula taking into account width of the track, track profile, earth gravity at the very point the track is laid and maximum centrifugal acceleration allowed, so I stop here. It is good enough to remember that the lover the number the less comfortable drive for passengers and safe carriage of the goods. If the number is too low, train will leave the track and become airborne.

So, if you want your train to travel with maximum speed of 160 km/h, calculated minimum radius of the track is (160 / 4.6) ^ 2 = 1210 m. If you already laid track in which the sharpest curve has only 150 m and you wonder at what speed trains should negotiate this curve, you can reverse the above formula

Vmax <= k * SQRT(R)

where SQRT is sqare root function of the argumet inside ()

and calculate max. speed as 4.6 * SQR(150) = 56 km/h.

Apart of it, there are two major concerns when laying curved track on a real railway:

- Curve with radius smaller than 1500 m result in significantly faster wear of rails and rolling stock

- Curve with radius less than 600 m make impossible to weld separate rails into longer section or they will break after a short time.

As to transitional curves - they are not needed in TRAINZ, but necessary on a real railway in order to minimise the impact of CF (Centrifugal Force) on the rolling stock, track and passengers or load. It is actually not the magnitude of CF that is so damaging, but the rate with which this force grows when a train moves from a straight track into a curve. Theoretically, on a straight track CF is zero. As soon as train enters even most gentle curve, CF grows to some value and we know that if something grows from nothing in an instant, it grows with infinite rate. If trains were 100% rigid they would break up on any curve, at any speed. But in reality some of CF is absorbed by couplers, boogies, wheels and undercarriage. Despite TRAINZ are totally CF resistant (they do not have mass, they exist only in computer memory), I believe you can still notice that a train runs a little smoother if you add transitional curves. There is no tool to build transitional curve in TRAINZ and if you connect two sections of a straight track using curve track, Surveyor tends to do exactly the opposite - it makes curve near the straight sections sharp and the one in the centre of the curve smooth. On a real railway this method would be disastrous! People would fly out of the windows and coal hoppers would arrive empty if arrive at all. It can be fixed by pulling the inner splines (i.e. splines not adjacent to the straight section) slightly away, i.e. in the direction opposite to the centre of the curve. What I do is to make sure the inner splines hold the minimum radius and I allow the splines connecting straight track to have radius 50% or even 100% bigger. In this method, when you run a train you will notice that it engages the curve in a very smooth motion. Of course the longer the transitional curve the less space you have for the remaining track, so you need to balance your design.

This is all for now, I leave more for later on. Sorry for this longish reply, but for me writing about TRAINZ is almost as much fun as building or driving them.

I wish you all good luck in never ending TRAINZ struggle,

Legia