Drawing roundabouts can cause some confusion because the Polyline Circle tool intersects itself at the top and is unable to connect as a routing node. This tutorial aims to guide you through to correct that as otherwise, routing will fail through the roundabout.
The roundabout in Indera Mahkota, Kuantan will be used as an example in this tutorial. The coordinate is 3.828454 103.272614.
1. Draw roundabout with Create Object > Polyline : Circle > Give it a label, if any
2. Select Tool > Double click on roundabout > Properties Tab > Check Polyline has direction > Routing Tab > Check One way
3. Since we live in a left hand drive country, you need to change the direction of your roundabout to clockwise: Select Tool > Right click on roundabout > Reverse Polyline
4. Select Tool > Right click > Modify > Routing > Routeclass > Roundabout/Collector
5. Select Tool > Right click > Modify > Routing > Speedlimit > 40kph (Maximum 60kph)
6. Select Tool > Right click > Modify > Extend Elements up to level > 1 (since roundabouts cover a small area it does not need to be extended to a higher level)
7. Select Tool > Right click > Modify > Postal address > City > Choose corresponding city
8. Modify Tool > Right click at one of the Routing Node at the bottom > Split polyline
The roundabout has to be split into more than one polyline because a polyline cannot intersect itself. This will cause a never ending loop for routing.
The split can be done anywhere along the roundabout polyline, preferably at one of the exit or entry intersections.
9. Right click at all roundabout intersection > Connect to nearest nodes (including where the roundabout intersects itself). As a general rule, all routing nodes on a roundabout should be yellow in colour. If it isn’t, disconnect the nodes and reconnect.
If where the roundabout intersects itself is at the top but there aren’t any roads going into the roundabout at this location, consider moving the routing node to the nearest intersection. This saves on the number of routing nodes.
How not to draw a roundabout
Roads going into a roundabout should never be joined with the next road exiting the roundabout as this will prevent the GPS from announcing the roundabout exit correctly.
