Every map site I can find (google, mapquest, AAA etc) says that quickest route is through Rawlins on I-80 and then up 287, rather than I-80 to Rock Springs and North on 191 to Jackson. By quickest, Google says the 287 route is almost 1 hour faster. I've never driven this stretch but my gut is 191 is faster, they're the same amount of miles and staying on I-80 longer seems to me to ensure a faster trip. Maps.google.com says to expect an average speed of 41 mph on the 191 route, can this be? Another negative of the untrained eye with 287 is having to drive the distance of Grand Teton to come south in Jackson. With my research both 287 and 191 seem to by 65 MPH speed limit roads.
What am I missing here? it's like all the mapping systems are drawing off a flawed assumption. Even my GPS says to go 287.
Another factor is there seems to be about 4 construction projects going on along the 287 route, which I would think I'd be best avoiding.
Can someone with experience help? I'm rolling through in 3 weeks.

Thanks much!

Mapquest should be on the money, but check with VT member KimberlyAnn. She lives in Cody and knows the roads well...

When I used to live in Rawlins and we would visit Jackson, we would go I-80 up to 191 in Rock Springs, through Pinedale, and then up to 189 to Jackson. It definitely took a few hours (Wyoming is vast and open). I believe that the speed limit on 191 is about 65 mph...but that could have changed since the last time I was there as well. But it could be winding roads and weather that effects that avg of 41 mph. (Make sure you bring a long a jacket and a blanket, you never know what the weather will bring you in the Tetons.)

Not sure if you've ever been there before, but just a quickie bit of advice, make sure that when you're getting down to half a tank of gas, fill up. Towns are few and far between, and you might not hit a gas station anytime soon. (Not unless they've changed it since I was there last.) Don't let it get to below a quarter tank, because it could be a few hours before you hit the next town.

Hope this helps! :)

Man, that's a boring drive!
191 is still 65, except for through the little towns, and I-80 is 75 most of the way. I think it's saying to take 287 because it's a little shorter distance-wise, but is probably not accounting for the fact that I-80 has a much higher speed.
On the way out of Cheyenne, consider taking the back way to Laramie, Happy Jack Road (State Highway 210). It's a little hard to find off of I-25, but it's a much prettier drive and, I think, worth it.

I can only give you my best guess and gut feelings about your question. Alan is correct, that I live in Wyoming, but I live in the NW section 50 miles east of Yellowstone and therefore take a much different route when we travel south from Cody. I have heard that hywy 191 has increasingly mountainous terrain after you have traveled north for a time. As I looked at the map, I saw that both 191 and 287 have an area designated as a Scenic Byway. In Wyoming these will mean mountainous driving. Hyway 191 has a longer stretch of this type of road than does 287. From our experience with Scenic Byways in Wyoming, this means slower driving, probably lots of curves and steep grades. Depending on how twisty this mountain road is, this could very well get you down into the 41 miles per hours range. Not having driven either of these, I could not tell you for sure what either one of the Scenic Byways looks like, but since all your research says 287 is faster, and seeing that there is a longer stretch of mountain roads on 191, my gut feeling is more mountains, more turns, therefore slower driving on 191.

A separate question: Which is the more scenic drive, route 191 or 287? I will soon be drivig from Yellowstone to Saratoga, WY, and want to take the most scenic route. -Thanks