Zwieschutzweiche
A Zwieschutzweiche (Zw) is a switch that is required by two routes , which can be set at the same time because they are otherwise not hostile to each other, in different positions as flank protection .
function
If there is such a double protection case, the switch can only give one of its strands edge protection, the other remains unprotected by the switch. To cross journeys to avoid on the other strand course, must be a spare protection be found. This is taken over by a guideway element in front of the point of the switch. Since this is further away from the protective journey, one also speaks of remote protection .
An intermediate switch can be used as a flank protection for a single route or for several routes. In the first case (so-called self - locking switch ), the switch is usually locked in the position in which a larger flank protection area is created for the protective route. In the second case (so-called real intermediate switch ), the switch in older signal boxes is only locked in the route that is driven on at higher speeds. The remote protection is permanently assigned to the other route. Most types of relay or electronic interlockings recognize the occurrence of double protection and only then close the remote protection. As a rule, the locking of the intermediate switch is then released.
In some countries, it is possible to dispense with direct flank protection for intermediate safety switches, so that neither the switch nor a replacement protection must be locked for the setting of some routes.
Situation in Germany
In Germany, interlocking systems for federal railways have only been approved since 1980 if intermediate switches to routes in main tracks are securely locked with signaling . For non-federally owned railways, in side tracks and before 1980, simpler, sometimes country-specific regulations apply. If a double protection lock is not technically possible, the restriction can be set that only one route can be set at a time. If routes are used a lot, this has a negative effect on capacity.
Situation in the Netherlands
In the Netherlands , the intermediate gate is deliberately not locked. The flank protection is determined that would apply in most cases. This was decided due to the very high train density in connection with the required reliability of the signal system and the available routes / station capacity.
Situation in Great Britain
In Great Britain , in individual cases, the intermediate switch is equipped with one switch drive per tongue. This means that if a train drives unauthorized on the secured route, it would derail in the intermediate switch.