Garmin 3598 aversion to using M4 / M48 bridges

[Dabri]

Tried to travel from England to Wales yesterday (about an hours drive for me), but the 3598 insisted that it would take 3 hours! Certainly there were traffic problems around Bristol, but 3 hours - why? It turned out that the 3598 wanted to go via Gloucester, until I drove over the M48 bridge. Even then it still insisted on avoiding both bridges on the return trip. I had another look at the 3598 today and it still had the same problem. When I tried the same route today on an older unit, 2460, it had no problems. I can't see any odd settings or preferences on the 3598. Has anyone else had a similar M4/M48 bridge avoidance recently, or know of a general Garmin oddity causing this? I don't feel that I can trust the unit when it does this.
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Dabri.
Navman iCN530T; Garmin 760T v4.80; Garmin 765T v4.00; Garmin 2460LMT v3.60; Samsung S3;
Garmin 3598LMT-D v5.50; Samsung J6; Garmin DriveSmart76 LT-D v6.80; Samsung A52.

[Kremmen]

There certainly are some SatNav oddities.

I've known major roads not being joined properly in the mapping so the SatNav logic refuses to route that way.

I used to travel up the M40 to Malvern. The SatNav would show I had over an hour to go and over 80 miles.

Once I turned off the M40 at J8 to use the Oxford bypass and via Woodstock it recalculated at took both distance and time off the journey.
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Satnav:
Garmin 2599 LMT-D (Indoor test rig)
DashCam:
Viofo A119 V3
Car Average MPG :

[sussamb]

Don't suppose you have avoid toll roads set on one and not the other?
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Where there's a will ... there's a way.

[Dabri]

Thank you for the thought, but no I haven't. P.S. There are no tolls on these bridges now.
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Dabri.
Navman iCN530T; Garmin 760T v4.80; Garmin 765T v4.00; Garmin 2460LMT v3.60; Samsung S3;
Garmin 3598LMT-D v5.50; Samsung J6; Garmin DriveSmart76 LT-D v6.80; Samsung A52.

[Kremmen]

I've never set off on any journeys in unknown territory without looking up the route first.

SatNavs are good once you get within 10 miles or so and need to navigate minor roads but for the majority of the journey, motorways and or A roads, I have it pre-planned subject to traffic reports.
_________________
Satnav:
Garmin 2599 LMT-D (Indoor test rig)
DashCam:
Viofo A119 V3
Car Average MPG :

[Dabri]

Mea culpa. sussamb was on the right lines. I had previously selected 'avoid motorways' for a journey, and not deselected it (although I thought I had). Duh.
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Dabri.
Navman iCN530T; Garmin 760T v4.80; Garmin 765T v4.00; Garmin 2460LMT v3.60; Samsung S3;
Garmin 3598LMT-D v5.50; Samsung J6; Garmin DriveSmart76 LT-D v6.80; Samsung A52.

[sussamb]

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