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Author Topic: How to deal with changing speed limit rules.  (Read 276 times)

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Offline Vladki

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How to deal with changing speed limit rules.
« on: October 23, 2020, 05:11:05 PM »

this is a bit of theoretical question about speed limits.

Top speed limit of a given way, is given not only by it's physical features (materials, construction, maintenance, age), but also by security limits imposed by government. While the physical limits are getting better over the time, the security limits have sometimes been made more strict recently.  E.g. road speed limits in towns in Czechoslovakia went like this: 1905: 15 km/h; 1935: 35 km/h; 1961: 50 km/h; 1975: 60 km/h; 1997: 50 km/h.   Similarly for roads outside towns, there was no limit between 1960 - 1979. Also during the times different limits applied for passenger cars, trucks and buses, different limits on normal roads and motorways.  If the limits would be rising only, that would be fine. One could introduce new ways (and vehicles) with higher limits, but what to do when the limits were reduced. One could retire the way in question, but the existing ways would still allow faster speed.   

For city limits, this could be implemented as timeline for the limit (like timeline for city roads), instead of one limit valid forever. But how about intercity roads? Also the higher limit for motorways is not only due to the better quality, but especially because the road is one-way. Could this be a way to implement out-of town limits, one that would apply to bidirectional roads, and one for one-way roads? Then it would be possible to have 3 separate time dependent speed limits (city, two-way, one-way). And the limits in dat files would represent only the physical limits of given way. Also different limits would be needed for private cars (and even some players vehicles), buses and trucks.

Similar are the speed limits at railway crossings, although AFAIK here the limits have been only raised, not lowered.

I found similar problem with railway signalling. Current Czech rules limit train speed to 100 km/h on tracks without cab signalling (either the old Czechoslovak system, or ETCS). Probably since 1995. But trains and tracks capable of >100 km/h were available since 1930's long before the cab signalling was invented. So the top speed for old signals would have to be cca 120 km/h before 1995 and then reduced to 100 km/h. So again a situation where a speed limit for existing infrastructure would have to be reduced.

Any ideas how to deal with these situations?