Why different distances & ETA: Streets & Trips, Google, Trailer Life Directory

I am from Europe and I am planning our trip to the North-west of the US. I bought the Streets & Trips software and started to plan. Before I bought the software I planned our trip with the Google Maps. During the planning I realized, that I sometimes get completely different figures regarding trip time. Here is an example: Trip from Columbia Falls, MT to Butte, MT (via MT-83)

Street & Trips 2010
Approximate Trip Mileage: 247 Miles
Approximate Trip Time: 3 hours, 42 Minutes

Google Maps:
Approximate Trip Mileage: 233 Miles
Approximate Trip Time: 5 hours, 26 Minutes

RV Camping, RV Parks, RV Campgrounds & Travel Guides - Trailer Life Directory
Approximate Trip Mileage: 234.92 mi.
Approximate Trip Time: 4 hours, 48 minutes

Does anybody know why I have this big difference between the different map software? Streets & Trips is at least one hour less than the other ones?

I can make it 4:03 if I slide the S&T route options driving speeds down to the slowest available.

As this is a pretty-straightforward route, I can only assume that the others use real slow speeds. The google route is slightly longer and goes through more towns and that will slow you down. Or it would slow ME down.
Ken in Regina
I tried it with:

Streets & Trips 2010:
235mi, 3hr 26min (MT-83S, I-90E)

Garmin Mapsource 2010:
235mi, 3hr 42min (MT-83S, I-90E)

Google Maps:
*233mi, 5hr 26min (MT-83S, I-90E)*
242mi, 5hr 1min (MT-35E, I-90E)
316mi, 6hr 12min (MT-28W, I-90E)

I have been using Garmin Mapsource and Garmin navigation devices for a number of years and I have found Garmin's routing calculations are generally useful for estimating just the driving time. When they say "driving time", that's exactly what they mean.

Based on my experience with Garmin's route calculations and the fact that I used maps that are from the same supplier (Navteq) as Microsoft uses for Streets&Trips, I would say that Streets&Trips route time is also useful for estimating driving time.

In both cases, I think they are a bit optimistic unless you drive fast and steady. If you assume a 65mph speed limit you would have to average 65mph to do it in the 3hr 42min Garmin thinks it will take..

I usually do a sanity check based on the mileage divided by my usual driving habits rather than just assume the routing program knows anything useful about driving speed. For a 233mi distance through that part of Montana I would expect to spend closer to four hours of actual driving time, not including any stops. That would allow for driving mostly at 65mph which for me would yield an average speed over that distance of about 60mph.

You will have to factor in the way you plan to travel to get anything useful from any of these estimates. That is, if the trip is long enough and at a time of day that will include a meal stop and/or fuel stop, you need to add that. If you plan to do some sightseeing you will need to add that.

I have too little experience with Google Maps to have any idea about their time estimate. From the distance of the MT-83/I-90 route it's obvious they have the distance correct so they are clearly making different assumptions about driving speeds. The 5hr 26 min driving time estimate seems to allow for a liesurely meal or some sightseeing along the way.

Originally Posted by Ken in Regina
...If you assume a 65mph speed limit you would have to average 65mph to do it in the 3hr 42min Garmin thinks it will take..
That may indeed be the case... If I recall correctly the speed limit on interstate highways in Montana is 70 mph, and may possibly be 75 on places.

...and most traffic seems to exceed it!
Ken in Regina
I can remember riding my motorcycle down there in the 70's when there was no speed limit.

I live in Montana. The speed limit is 75 on almost all interstate highways. It is 70 on most other highways. You can get away with going MUCH faster in central and eastern Montana, just don't try it in the "more populated" western part.
Montana had NO speed limits until the late '90's! They had to start imposing speed limits or lose highway funding.
BTW, a passenger could have open containers of alcohol until 3 yrs ago!
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