Routing Class & Speed Limits
So far this affects the drawing (and drawing order on GPS) of the roads and highways on maps.
In order to “adjust” or control how auto routing calculations behave, we still have to make changes in the Object Properties – Routing tab
Click on the polyline/road, right click, select Properties.
Then select the Routing tab.
Two main things to adjust here are:-
Routing Class and Speed Limit
Ever had the uncanny experience of GPS unit reporting your ETA at a destination and arriving almost exactly on time!
Well, this is all "controlled" on the maps here on this tab by a mapper.
This is independent of the polyline type code used (which is for display/drawing purposes only).
routing calculations, there are only four main types that can be
selected in spite of more road types available at a map display level
shown earlier above.
0.Residential Street/Unpaved road/Trail
1.Roundabout / Collector
2.Arterial St / Other HW
This determines the routing priority for the maps and the polyline type should match routing class.
If you used a Major Highway polyline type used (0x01) then you should also change the Route class to 4. Major HW/Ramp under the Routing tab
You may have noticed on your GPS unit and Mapsource, an option to select "Shorter Distance" or "Faster Time", well here is where it all starts.
explained earlier in the tree and leaf analogy, routing calculations
will place higher priority on 4 and then go in descending order to get
you to your destination faster as far as practicable on the polylines
and routing settings defined on the maps.
An item, not covered earlier is Route class 1 – Roundabout/Collector.
If you have roundabouts drawn, this route class should be selected in order for GPS unit to either alert you with routing instructions that includes something like:-
“…take second exit at roundabout…”
(speech instructions in speech capable units like Garmin Nuvis or text instructions in auto routing capable Garmin units)
you haven't selected this but have drawn a roundabout polyline type on
the maps, nothing happens on the routing instructions on your GPS.
Forget about the usual connotation around speed limits.
This is not the actual speed limit on the real roads (but can be sometime!)
Garmin and GPSmapedit has limited this to seven speed categories as shown below
0. 3 mph / 5 kmh
1. 15 mph / 20 kmh
2. 25 mph / 40 kmh
3. 35 mph / 60 kmh
4. 50 mph / 80 kmh
5. 60 mph / 90 kmh
6. 70 mph / 110 kmh
7. No speed limit
It is more about a setting that can be used by mappers to more accurately
route you to a destination based on known traffic conditions and / or
road conditions prevailing at the time and location.
Sometimes on a particular stretch of road due to certain traffic conditions and obstructions (eg, roundabouts and traffic lights), it is possible that a mapper may choose to break up a road into different speed limit classifications to enable a more accurate GPS routing calculation and hence more accurate ETA.
Sometimes a Major HW that on the open highway road may have a speed limit of "6. 70mph / 110 kmh" but can be reduced down to "3. 35 kmh / 60 kmh" if it goes through a city or town and then "speeds up" again to 80kmh and then up to 100kmh leaving the city or town (this is very common in places like New Zealand).
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