Is there a way to plan a trip showing speed limits of the route?

If you can't calculate that then why ask someone else?

14.5 is driving time. Google also shows total distance. Take the total distance and divide that by what ever speed you think you can average and this will be the new drive time.

Keep in mind drive time does not include necessary stops. Every two hours (or less) a driver should take at least a fifteen minute break. Fuel stops are needed every 300 miles or so. A meal break about every four hours.

Plan on the grades! If you are from Washington state you should know what I mean. Also depending on the route, 60 miles per hour would be impossible. The drive down the snake river is not a sixty mile per hour road! Not that you will have to go that way. Even from San Fran it will take about two days driving to get to Wyoming.

When you use the Internet, try mapquest.  It give you the travel time and distance.  Divide the distance by the travel time and you get mph...miles per hour.

Yes, there is a way, I know of a way, and so do many other people, which answers your question. If you would like to know HOW, you should have phrased your question a bit differently.  

 Just plan for an average of 50 mph. This will take into account all the stops

DUH!   60 mph is mile a minute -- miles is same as minutes.  A 900 mile trip will take 900 minutes.  If you can't figure the math, that is 15 hours.

That is "windshield time" actual on the road.  Figure two hours a day with lunch break, gas breaks, rest breaks, kids dropped things out the window go back and get it back breaks....

Simply take the trip length and divide by your speed to get hours.

Example, 1085/55=19.72

Keep in mind you will average a speed lower than intended due to fuel, food, or rest stops etc.

you might be able to get that info online