Audio Lane Guide
By Jason Lee
PREAMBLE: The voice prompt feature of the Garmin Nuvi GPS is under-utilised. It remains silent most of the time when routed to go straight and is thus not of much help to guide users through city streets when not routed to make turns. Particularly in certain cities, streets are fraught with danger of sudden changes without notice that can be both frustrating and costly for the unfamiliar motorist.
The Problem
Especially in Penang, many roads with more than one lane will suddenly change attributes without warning. Often the motorist sees both lanes painted with a white arrow that indicates going straight so if the motorist happens to take the inner lane and intend to keep going straight, the motorist may find that lane suddenly becomes an exclusive right-turn lane or U-Turn lane without warning. It is frustrating enough to be stuck behind traffic that is stopped and waiting for the lights to change while traffic in the outer lane is free flowing. To add insult to injury, if the motorist tries to change lanes in the last 100m, he may get a ticket because many of such lanes are segregated by double-white lines, making lane change a costly affair.
Is it safer then to keep to the outer lane? The answer is unfortunately no because often the outer lane may also suddenly change to a turn-left-only lane or they may be blocked by illegally parked cars or hawker carts. If the motorist is not familiar with the road it may leave him bitter with the city he's visiting.
What is Audio Lane Guide (ALG)?
This feature makes use of the voice prompt to guide an unfamiliar motorist when to change lanes (not to exit or turn) on hearing "KEEP LEFT" or "KEEP RIGHT" to stay out of trouble. Since the GPS voice prompt is rather rudimentary and can only say "KEEP LEFT" or "KEEP RIGHT" or stays silent, it works only for roads with not more than 3 lanes. When there are more than 3 lanes, the motorist will need Lane Assist or Junction View to help the motorist out. But as Lane Assist is not designed for guiding motorists while routed to go straight, this Audio Lane Guide can complement even GPSrs with Lane Assist.
ALG is applied to intersections with exclusive right-turn and/or U-turn lanes to make the voice prompt say "KEEP LEFT" to guide the motorist away from those exclusive lanes.
ALG only works when the GPS is routed to a destination.
The Principle Behind ALG
The algorithms of the GPS have sufficient logic to guide the user to change lane or direction when it encounters a new road or a change of road attribute. The principle is to present such a change in road attribute to force the GPS to issue a voice prompt of “KEEP LEFT”. When travelling straight along a one-way street which suddenly becomes a 2-way road what is the logical thing to do? Keep left of course (in countries that drive on the left side of the road). Keep right is not an option (unless driving is on the right side of the road). The GPS has been programmed to recognise that and issue the appropriate voice prompt.
The Technique
A. For dual-polyline roads
3 things need to be done to be done to trigger the voice prompt:
1. Provide a one-way branch to the one-way trunk polyline to represent the exclusive right-turn and/or U-turn lane.
2. The one-way trunk polyline must be split at the node where the branch is, to establish that the polyline that continues on straight after the branch node is ‘no longer the same road’.
3. The one-way trunk polyline must be split again about 10-15m from the branch node to be the trigger segment. This trigger segment’s routing attribute must be changed to two-way. To avoid confusing the user into thinking that something is wrong with the map, keep the Road Type attribute of ‘Polyline has direction’ checked (so the one-way arrow will still be displayed) and delete the road name and leave it blank (to reduce the clutter of road labels). The purpose of keeping this trigger segment short is to prevent accidental wrong routing against the actual traffic flow. The trigger segment must also not be connected to any node with a side road connected to avoid routing error.
T = two-way trigger segment (10-15m length)
Things to note:
i. The angle of the branch at the branch node must be around 30°. This is to make the GPS recognise the branch to ensure correct routing and to trigger the voice prompt of “KEEP RIGHT” when routed to drive along the branch. This is crucial. If the angle exceeds 45°, the voice prompt will say “TURN RIGHT” instead of “KEEP RIGHT”. If the angle is too small, the branch may not be recognised by the GPS and will not route into the branch. [When routed to go straight, the ALG prompt of “KEEP LEFT” will be issued.]
ii. It will be useful to label the branch appropriately as ‘right-turn only’ or ‘U-turn only’ or ‘right-turn or U-turn’ or it can also be left blank.
iii. The Road Type of the trunk should not be changed so as not to mess up the map. The road type of the branch can be anything but it is better to use a lower level road type (represented by a thinner polyline) so that it will not be so noticeable in the map (since there is no real branch road).
iv. To further conceal this branch, you can tack it to run close to the parallel polyline which it connects to for turning right or U-turn. If the branch allows a U-turn, the angle where it connects to the parallel polyline must also be around 30°. If configured this way, the voice prompt will say “KEEP RIGHT THEN TURN SHARPLY RIGHT” when making a U-turn instead of saying “TURN RIGHT THEN TURN RIGHT”. Unfortunately I have not learnt how to make it say “KEEP RIGHT AND MAKE A U-TURN”. If turning right, the voice prompt will say “KEEP RIGHT THEN TURN RIGHT”.
v. Make sure all node attributes are verified to produce the correct routing and test the routing in MapEdit for both faster time and shorter distance. Ensure that it works at least for faster time.
vi. The length of the branch must reflect the actual road conditions so that the voice prompt timing will be correct. The exclusive right-turn lane is usually about 100m. An average motorist may need 6-7 seconds to respond and change lanes successfully. If travelling at 80kph, this means about 150m. Hence the point at which the final voice prompt is heard must be about 250m from the point the branch makes the turn to the parallel polyline. The GPS issues the final voice prompt of “KEEP LEFT” about 70-80m before reaching the branch node. Hence the branch length should be around 250m-70m = 180m. A length of 180-200m will produce good results. This length should be adjusted to the actual road conditions – sometimes shorter and sometimes longer may be necessary.
B. For single-polyline roads
This technique can also be applied to roads which actually have 2 lanes on each side but represented by a single polyline because it is not a true dual-carriageway with a divider in the middle.
If the inner lane is used for turning to side roads, then using this technique, the GPS can advise the motorist to “KEEP LEFT” and use the outer lane as a bypass lane to avoid the traffic waiting to turn right in the inner lane.
The technique to create the trigger is the same as for dual-polyline roads except it is now created on a virtual Bypass Lane.
Things to note
i. The trigger segment follows the same configuration as for dual-polyline roads.
ii. Consider the Bypass Lane as the branch but the branch angle at the branch node can be smaller - around 10-20°. After that, the rest of the branch can be tacked close to the original polyline to conceal it as the branch is also a virtual road so should not be seen on the map. The Bypass Lane must be one-way and the trigger two-way but disguised as a one-way.
iii. The Road Type of the branch can be the same as the original road or of a lower level but as long as it is tacked close the original polyline, it will not be seen.
iv. It is crucial that the node(s) along the original polyline which connects to a side-road must be edited to prevent straight through traffic flowing in the same direction as the Bypass Lane (to force straight-through traffic into the Bypass Lane) while straight-through traffic from the opposite direction is allowed and the polyline remains a 2-way polyline and allow traffic to enter or exit the side-road from both directions (if that was originally allowed).
v. Test routing in MapEdit and increase the speed limit of the Bypass Lane (or reduce the speed limit of the original polyline or both) to ensure Faster Time routes through the Bypass Lane successfully. It is more tricky to get Shorter Distance to route through the Bypass Lane because the branch angle will make the Bypass Lane naturally longer (unless the original polyline is a curve) but it is possible to introduce a gentle and imperceptible zig-zag to the original polyline to make it longer and allow Shorter Distance to also route through the Bypass Lane. This technique is necessary when there is more than 1 right-turn intersections to bypass and obviously then through traffic to the second or subsequent intersections must be allowed at the first right-turn node thus removing the mechanism to force routing through the Bypass Lane. The length of the Bypass Lane is not important (as long as it bypasses the right-turn lanes) so the mapper can decide on the length based on the layout of the original polyline (depending on how many intersections it has to bypass) however, since it is a virtual road, keeping it short will help to conceal it. Several shorter ones can be created instead of one very long one (and helps to remind the motorist to keep left as there are more triggers).
This is a new and unusual feature so to make it work you must be prepared to think out of the box and do things a little differently from the usual way you draw maps.
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2. The one-way trunk polyline must be split at the node where the branch is, to establish that the polyline that continues on straight after the branch node is ‘no longer the same road’.
3. The one-way trunk polyline must be split again about 10-15m from the branch node to be the trigger segment. This trigger segment’s routing attribute must be changed to two-way. To avoid confusing the user into thinking that something is wrong with the map, keep the Road Type attribute of ‘Polyline has direction’ checked (so the one-way arrow will still be displayed) and delete the road name and leave it blank (to reduce the clutter of road labels). The purpose of keeping this trigger segment short is to prevent accidental wrong routing against the actual traffic flow. The trigger segment must also not be connected to any node with a side road connected to avoid routing error.
T = two-way trigger segment (10-15m length)
Things to note:
i. The angle of the branch at the branch node must be around 30°. This is to make the GPS recognise the branch to ensure correct routing and to trigger the voice prompt of “KEEP RIGHT” when routed to drive along the branch. This is crucial. If the angle exceeds 45°, the voice prompt will say “TURN RIGHT” instead of “KEEP RIGHT”. If the angle is too small, the branch may not be recognised by the GPS and will not route into the branch. [When routed to go straight, the ALG prompt of “KEEP LEFT” will be issued.]
ii. It will be useful to label the branch appropriately as ‘right-turn only’ or ‘U-turn only’ or ‘right-turn or U-turn’ or it can also be left blank.
iii. The Road Type of the trunk should not be changed so as not to mess up the map. The road type of the branch can be anything but it is better to use a lower level road type (represented by a thinner polyline) so that it will not be so noticeable in the map (since there is no real branch road).
iv. To further conceal this branch, you can tack it to run close to the parallel polyline which it connects to for turning right or U-turn. If the branch allows a U-turn, the angle where it connects to the parallel polyline must also be around 30°. If configured this way, the voice prompt will say “KEEP RIGHT THEN TURN SHARPLY RIGHT” when making a U-turn instead of saying “TURN RIGHT THEN TURN RIGHT”. Unfortunately I have not learnt how to make it say “KEEP RIGHT AND MAKE A U-TURN”. If turning right, the voice prompt will say “KEEP RIGHT THEN TURN RIGHT”.
v. Make sure all node attributes are verified to produce the correct routing and test the routing in MapEdit for both faster time and shorter distance. Ensure that it works at least for faster time.
vi. The length of the branch must reflect the actual road conditions so that the voice prompt timing will be correct. The exclusive right-turn lane is usually about 100m. An average motorist may need 6-7 seconds to respond and change lanes successfully. If travelling at 80kph, this means about 150m. Hence the point at which the final voice prompt is heard must be about 250m from the point the branch makes the turn to the parallel polyline. The GPS issues the final voice prompt of “KEEP LEFT” about 70-80m before reaching the branch node. Hence the branch length should be around 250m-70m = 180m. A length of 180-200m will produce good results. This length should be adjusted to the actual road conditions – sometimes shorter and sometimes longer may be necessary.
B. For single-polyline roads
This technique can also be applied to roads which actually have 2 lanes on each side but represented by a single polyline because it is not a true dual-carriageway with a divider in the middle.
If the inner lane is used for turning to side roads, then using this technique, the GPS can advise the motorist to “KEEP LEFT” and use the outer lane as a bypass lane to avoid the traffic waiting to turn right in the inner lane.
The technique to create the trigger is the same as for dual-polyline roads except it is now created on a virtual Bypass Lane.
Things to note
i. The trigger segment follows the same configuration as for dual-polyline roads.
ii. Consider the Bypass Lane as the branch but the branch angle at the branch node can be smaller - around 10-20°. After that, the rest of the branch can be tacked close to the original polyline to conceal it as the branch is also a virtual road so should not be seen on the map. The Bypass Lane must be one-way and the trigger two-way but disguised as a one-way.
iii. The Road Type of the branch can be the same as the original road or of a lower level but as long as it is tacked close the original polyline, it will not be seen.
iv. It is crucial that the node(s) along the original polyline which connects to a side-road must be edited to prevent straight through traffic flowing in the same direction as the Bypass Lane (to force straight-through traffic into the Bypass Lane) while straight-through traffic from the opposite direction is allowed and the polyline remains a 2-way polyline and allow traffic to enter or exit the side-road from both directions (if that was originally allowed).
v. Test routing in MapEdit and increase the speed limit of the Bypass Lane (or reduce the speed limit of the original polyline or both) to ensure Faster Time routes through the Bypass Lane successfully. It is more tricky to get Shorter Distance to route through the Bypass Lane because the branch angle will make the Bypass Lane naturally longer (unless the original polyline is a curve) but it is possible to introduce a gentle and imperceptible zig-zag to the original polyline to make it longer and allow Shorter Distance to also route through the Bypass Lane. This technique is necessary when there is more than 1 right-turn intersections to bypass and obviously then through traffic to the second or subsequent intersections must be allowed at the first right-turn node thus removing the mechanism to force routing through the Bypass Lane. The length of the Bypass Lane is not important (as long as it bypasses the right-turn lanes) so the mapper can decide on the length based on the layout of the original polyline (depending on how many intersections it has to bypass) however, since it is a virtual road, keeping it short will help to conceal it. Several shorter ones can be created instead of one very long one (and helps to remind the motorist to keep left as there are more triggers).
This is a new and unusual feature so to make it work you must be prepared to think out of the box and do things a little differently from the usual way you draw maps.
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