Service Road affects routing?

[AggieJM]

I've noticed an odd routing behavior, but I'm not sure if I'm seeing the right cause.

If you're on the far north side of Dallas, TX (Frisco) and heading to a destination south of Dallas on I-35E, the fastest route is to take the Dallas North Tollway south to I-35E in downtown. At the end of the DNT, there is a ramp that you leave the DNT that puts you onto the I-35E service road, then a few feet later you take the ramp onto I-35E. Service road segment highlighted in this permalink:

https://www.waze.com/editor/?zoom=3&lat ... s=49823859

Whenever I route through here, Waze will always suggest DNT to I-635 west, to I-35E south. But as I drive down the tollway and get within a few miles of I-635, the routing will update to skip I-635 and use DNT all the way into downtown.

Is this cause by the longer route opting to not use the Service Road, then as I get further down the DNT, the route is shorter and the Service Road becomes an option? Or is there something else that I should be looking for?

[CBenson]

I don't know, but think that it is a very plausible theory. I don't have much experience with the routing properties of service roads, but have always been told that they are similar to street segments. I would be very interested to know if the long distance routing changed if that segment were changed to ramp type.

[ncc1701v]

Waze has utilized service roads well for me in Queens NY - they can be noticeably faster than the main freeway - but that's for short trips, only about 10 miles. I have two speculations about the routing algorithm:

(1) It doesn't deal with a fine level of complexity until you get close because it doesn't want to take traffic into consideration for the whole distance. Once you get close it's willing to do so.

(2) It has a rule about using freeways on trips above a certain rule-of-thumb distance; once you get below that distance it is free of that rule.

[jasonh300]

A service road will route just like a Primary Street, so it likely will be avoided on a very long route. It sounds from what you describe that the section of service road should be set to a highway type...probably a minor highway to prevent this from happening.

[CBenson]

Would not ramp type also prevent this from happening? The segment is between two ramp segments and it would seem to me to be much less likely to be "corrected" as a ramp segment than as the only minor highway segment within a half mile of that location. Either way, I would be interested to confirm that the long distance routing changes with a change to the road type here.

[jasonh300]

A ramp would probably look not-as-bad-as minor highway.

[AggieJM]

If we just change that one segment of the service road, will it negatively affect any other routing along that service road? I'll make the change and test the routing after the next update, just wanted to make sure it wouldn't break any routing that uses a longer portion of that service road that includes that one segment.

[WeeeZer14]

If it wasn't for the parking lots between the two exiting ramps, I'd say to just extend the off-ramp further east so that it actually connects to the on-ramp. Then ramp to ramp traffic only sees ramp and service road through traffic only sees service roads.

The problems:
- coming off the off-ramp and having a decision between ramp and service road means the on-ramp will probably be the "best continuation" and you will NOT get a stay or exit left. Workaround: make the on-ramp branch off at a 90 degree angle to force a TURN left in all cases.
- if anyone maps those parking lot roads, they will either only connect to the service road or someone will make a huge mess.
- close parallel roads usually scream "mistake!" and someone will think it needs to be fixed.

[bgodette]

A better question would be: Why are you using "Service Road" for what's called an Urban Collector (eg Primary in Waze) under Functional Classification. Service Roads route exactly like Street and are subject to the same pruning rules.

[AggieJM]

A better question would be: Why are you using "Service Road" for what's called an Urban Collector (eg Primary in Waze) under Functional Classification. Service Roads route exactly like Street and are subject to the same pruning rules.

Wasn't my choice. All of the frontage roads to the major highways in the Dallas area are set as the 'Service Road' type. It's been that way since before I started editing. I just noted the problem it was causing on my trips through the area.