My Garmin 2450 gives a route from point "A" (Home) to point "B".

Fine, and then I would like to go from point "B" back to point "A"
(Home) on the same roads, but, my 2450 gives a somewhat different
route almost every time.  

Settings are "Shortest Time".

Why is the reciprocal route sometimes (almost always) different in
some way from the original route?

Anybody else experience this phenom?

Bob Flumere
rflum...@comcast.net

Yeah, me on a 200w.  I've always put it down to any of a number of
possible reasons including the time difference between routes being quite
small so more (or less) left (or right) turns might affect the timing, or
the type or junctions on the route, or maybe the time of day if the map
includes different average speeds on some or all of the route, eg mid-
morning as opposed to "rush"[1] hour.

I've even experienced different routes based on which way the car is
facing in the same parking spot when setting off home.  I have U turns
switched off so it will, I expect, calculate the route based on the
direction the car is facing at the time, only suggesting a U turn under
fairly extreme circumstances.

[1] Why is called rush hour when it usually last much more than an hour
and your rarely get to actually "rush"

--
DaveG
Lifetime member of the National Trust
6 years and counting.

On 26/05/2012 2:30 PM, Bob Flumere wrote:

  Yup. I've experienced the same thing. I live in a rural area and it
keeps wanting me to use  a longer travel distance to return home than
what it used to guide my to my destination. I thought maybe it would
eventually 'learn' after a few trips, but no, it keeps nagging me to use
it's selected return root every time I come to a cross road that
connects with it. The odd thing is, its desired return route is about
20km and 13 minutes longer than the route I normally use.

Gil

"Shortest time" means shortest time. Not shortest drive. The 2450 is a
trafficTrends unit, which means it takes notes about routes it sends you
down. Which means it learns which intersections take a long time to get
through at that time of day, which left turns are no big deal and which
take a long time get through, which roads that are posted as 45 MPH
really let you through at 45 MPH and which are congested enough that the
average is 30 (again, at that time of day), etc. It'll also try
different routes to see if they're better or worse than the detailed
information it has about the "obvious" fastest route. And it's picture
of where you drive and how much you speed routinely will also change
over time so that it can get better at selecting "fastest" for your
particular driving style and patterns.

As an example, my unit knows that the "obvious" direct route to the
interstate isn't the best. It's a six-lane US highway posted for 45
MPH that happens to also have six traffic lights on the length of it,
and three stop signs to get to it by the obvious route. If it takes a
zig-zag route out from my house that's "out of the way", it can skip
two stop signs and the one that it does encounter is a right turn. In
the afternoon, that 6-lane road's traffic lights are synced to traffic
flowing *into* town, not out to the highway. So in the afternoons, it
sends me down a 30 MPH semi-residential side street (instead of the 45
MPH main drag) that has comes out between the second-to-last traffic
light and the last one before the highway. It took me slavishly
following its directions, regardless of how dumb they seemed, for about
three weeks before it started working out to be faster ALL the time
instead of just most of the time, but now, yes, it really DOES know what
its doing better than I do most of the time, for that path.

--
"... I've seen Sun monitors on fire off the side of the multimedia lab.
 I've seen NTU lights glitter in the dark near the Mail Gate.
 All these things will be lost in time, like the root partition last
 week. Time to die...". -- Peter Gutmann in the scary.devil.monastery

On 5/26/12 2:30 PM, Bob Flumere wrote:

Obama's nanny DOT has mandated a different return route for added mental
stimulation and experience. On second thought, that's not it because
they want sheep, not thinkers...