FAQ: daytime dependent routing

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FAQ: daytime dependent routing

Postby Bernd Welter » Tue Jul 31, 2018 8:39 am

Hi there,

as the topic daytime dependent routing becomes more and more important and raises a large variety of expectations I'd like to gather some core facts for you. Feedback is welcome as well as further questions we might have to answer!

Best regards,
Bernd

  • Our routing is based on FL_SpeedPatterns. Looks like the speed is too optimistic in most cases. Is there any possibility to apply a correction factor to the dynamic speed manually? Answer:
    We also experienced such behaviour of the daytime dependency in some research projects. Our conclusion was that the variation of the speed values is too small. Our data department is working on that topic and we know that the speed values in the speed patterns are a bit too high. We also discussed this with our data providers. Besides the regular PTV_SpeedPatterns for cars we also offer truck based speed patterns (PTV_TruckSpeedPatterns) which contain downgraded speed values based on the regular car patterns.

    Within one research project we experimented with a "stretching factor" approach but this concept never made it's way into the servers. Within xServer1 we offer the so-called "speed mapping" in the profile: Routing/Course/DynamicRouting. This enables you to define piecewise linear functions which can be used to manipulate the speed values from the feature layers. This mapping is used to transfer the FL speed to the effective speed. Attention: this works with xServer1 only. If you want to benefit from this in tour optimization you have to activate it in the DistanceMatrix calculation. Also check the FreeFlowSpeed: The speed mapping can be applied also together with the free-flow speed, see also the last answer.
  • Can we apply this routing in xTour to be part o sequencing or tour optimization?
    At the moment there's only one dima per vehicle but we work on prototypes enabling us to handle time dependency in a more flexible way. We want to provide some features dealing with this in late 2018.
  • What is the meaning of FREEFLOW? I see strange odd values (instead of speed limits) Answer:
    The data itself contains the free flow speed in km/hour and a integer based percentage value between 0 and 100 depending on the time of the day (interval precision of 15minutes). The original free flow data comes from our major providers such as TomTom and we do not know how they are related to the legal traffic signs. Maybe the source of the data is the set of mobile navigation devices of TomTom. The data department later derives the truck speed patterns from the original car patterns. The definition of the correction is not public.

    Further info about the freeflow definition by provider:
    TOMTOM: 1.2.1 Freeflow Speed
    Used as a limit to Maximum speed values. Any probe value exceeding this speed is topped to
    the Freeflow Speed. This speed reflects the average speed measured during a period of least
    traffic congestion; most often these reflect nighttime speeds.
    HERE: no definition found so far.
  • How can I activate the FREEFLOW speed? Answer:
    Use the Routing/Course/DynamicRouting/@useFreeFlowSpeed parameter in xServer1.
    XServer 2 offers a specific time consideration mode know as „OPTIMISTIC“. Not 100% the same as with xServer 1 but likewise.
Bernd Welter
Manager Technical Consulting & Requirement Engineering
Senior Technical Consultant Developer Components
PTV GROUP - Germany

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