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HOW TO SET ROUTING CLASS AND SPEED LIMITS ON ROADS




This article is on how to correctly set routing class and speed limits for Garmin GPS maps ©



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

 

ROUTING CLASS

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).


For 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

3.Principal HW

4.Major HW/Ramp


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.

As 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.


ROUNDABOUTS

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)

If you haven't selected this but have drawn a roundabout polyline type on the maps, nothing happens on the routing instructions on your GPS.


SPEED LIMIT

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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