Ignoring "Preferred" Routing

[RVTravelerNTechie]

I'm working on a cross-country trip plan, breaking up travel into daily segments so the ETA info under GPS navigation will be accurate. I set a route from Eastland, TX to Shreveport, LA. All road types are "standard" except Limited Access as "preferred". SA2009 refuses to make the route I-10 to I-20, instead continuing on I-10 and then using US/State routes to head north to Shreveport. I was able to force it with a Via, but my mind is boggled about why it would ignore a valid Limited Access route and create one (both "quickest" and "shortest") that adds 100 miles to the route. Am I doing something wrong? Missing a trick? Thanks...

[wfooshee]

It appears that I-20 is not flagged in the map database as limited access. Going from Eastland, it took me to Dallas on I-20, picked up I-30, and then turned South to Shreveport on US-71.

It REALLY got weird if I told it to start in El Paso. Then it was I-10 to San Antonio, I-35 to Dallas, then again i_30 to US 71.

Setting Limited Access to standard gave me the expected I-20 all the way. Like I said, apparently I-20 isn't in there as "limited access" so it doesn't qualify as preferred, even though the El Paso to Shreveport route was almost 200 miles longer, and the Eastland to Shreveport route was 75 miles longer.

In your post, though, I'm not sure what I-10 has to do with Eastland. Nowhere near! (That's why I tried the El Paso start, just to see.)

[txyank]

Is there more than 1 Eastland, TX? I put in to route from Eastland, TX to Shreveport, LA and it took me on I-20 all the way. The Eastland my program pulled up was slightly Southwest of Ft. Worth.

[Dan Lawyer]

Actually, I think I heard something like this lately from someone else. If you leave the Route Prefs at default, and don't set Limited Access to Preferred, it will use I-20 all the way. There definitely is something wrong with this, and it's happening in 2010 too.

[John Moran_2]

If I recall correctly, a Delorme route will stay on I-20 for (almost?) its entire length using default settings in the latest Topo versions. To me this sounds good, but it is possible that it does this because of the long distance 'hub" routing that was created for the PN-40.

I know this seems off topic to Street Atlas users, and maybe it is for SA2009. On the other hand I-20 is a pretty straight road, and maybe the routing engine is just doing its job correctly from end to end of that particular route.
JM_2

[wfooshee]

Yes, with default settings it routes his route correctly using I-20. When he sets "Limited Access" to "Preferred" is when it all goes to hell. It works very hard then to avoid I-20, which makes it a problem with how I-20 is flagged in the database.

[John Moran_2]

Not exactly. It seems that the ramp at the interchange from I-10 eastbound to the beginning of I-20 eastbound is the culprit, if we are talking routing from I-20 from the beginning. I have seen no comment on whether another Eastland Texas may exist in the area of the I-10 to I-20 interchange, but perhaps any onramp that did not fit the "Limited Access Hwy" Preferred criteria might cause a problem.

Coordinates N31.089463°,W104.052840°

Usually a reset to Default in Advanced Routing Preferences will get the routing engine working pretty well again.
JM_2

[Dan Lawyer]

FWIW...
The standard routing will by default, "prefer" limited access roads for the quickest route, simply because their speed for any distance is faster. The only case where you might need to set limited access roads to preferred would only be if you weren't near interstates and it had to go out of it's way to get to one. In most cases, this isn't an issue and the Quickest routing will work with road types left at the default settings.

When you get an obvious weird route (usually a road break or classification error), then inserting a VIA will normally solve the problem without messing with the road type defaults.

DeLorme is aware of this issue in 2010, but it's not something they can fix until the next version.....If you have Topo 8, it does your route properly.

[John Moran_2]

.....If you have Topo 8, it does your route properly.

Sorry, Dan, but Topo8 has the problem also. I used it in my tests, as I have no Street Atlas versions past SA2008+.
JM_2

[xapie128]

DeLorme is aware of this issue in 2010, but it's not something they can fix until the next version.

This error is present in SA2008, SA2009, SA2010, Topo 7, and Topo 8.
Most likely before that, but that's all the versions I have available to check right now.

Since this Routing error has been around for years, and they haven't fixed it for five versions, I have serious doubts they are going to fix it the next time around.

[John Moran_2]

A few Ramp vector reclassifications might fix the "problem".
JM_2

[xapie128]

A few Ramp vector reclassifications might fix the "problem".

A good place to ask, again, that we can be given the ability to do that, so we can fix all the database errors and make a better program.
That and allowing us to define the Road Type to user added routable roads.

[Dan Lawyer]

Opps..my bad. When I tried it in T8 I forgot to set Limited Access to Preferred....duh..

Well, you would think since John found what is most likely the problem, maybe they will fix this one since they don't have to look for it.

[John Moran_2]

Opps..my bad. When I tried it in T8 I forgot to set Limited Access to Preferred....duh..

Well, you would think since John found what is most likely the problem, maybe they will fix this one since they don't have to look for it.

John votes for leaving it alone, as ramps are a necessary evil in routing in both SA apps and the PN-40. It does route correctly in the one available routing mode on the PN-40. It seems that anyone who is smart enough to find advanced routing in the SA apps is should be willing to take a little time to see how things work before driving 400 miles out of the way. YOMV. Your opinion may vary.

I don't slavishly follow PN-40 routing either, now that they sped up calculations by routing me south through the Los Angeles I-405/US101 interchange when I want to create a route northwest through Bakersfield. But the I-405/US101 Interchange works nicely for calculating routes through El Paso to Dallas.
JM_2

[xapie128]

~

I'm not sure if this is related to the "preferred routing" discussion here or not, but I did find something strange happening on I-20 eastbound . . .

• With Limited Access Route Prefs set to Standard, create a Route using the following . . .
  
  
• Place Start on I-20 eastbound anywhere between Dallas and the onramp at exit 556 (i.e. anywhere before N32.468336, W95.384226)
  
  
• Place the Finish, also on I-20 eastbound, anywhere between exits 560 & 562 (I used a point at N32.455654, W95.300863)
  
  
• Zoom in to the segment near exits 560 & 562, note that the Route follows the interstate, just like you'd expect it to
  
  
• Set Limited Access to Preferred and allow it to recalculate
  
  
• Click attachment below to see whole graphic with no scroll bars

Using "Preferred," the Route actually goes over top the Finish point, gets off the next offramp, double-backs on westbound, gets back on
eastbound, and ends at the Finish that it had previously passed over

One odd thing, and the reason I said I wasn't sure if this is related to the topic discussed here, is that if you move the Finish east of exit 562 then it doesn't act strange.
.