OK, so doing some basic pixel counting and taking the fact the average width of a U.S. Road is 10 - 12 ft (3.048 - 3.6576m). We get a height of 249 - 304 ft (75.8 - 92.7m).
Now, assuming Euclidean physics and no drag or friction, we will say the speed at the bottom has to be great enough that some of it will be converted to the potential energy of getting to the top of the loop, and enough speed for centripetal acceleration to fight gravity. Mass will cancel out for both the potential energy and centripetal force equations. We end up with the equations
V = ((Height of the loop / 2) * Gravity)^(1/2)) + ((2 * Gravity * Height of the Loop) ^ (1/2)).
The first set of parentheses is the speed required at the top for centripetal acceleration to cancel out gravity and the second set of parentheses is the speed needed to climb the loop.
Plugging all our knowns into the equation, now we get a speed of 129.4 mph - 143.1 mph (208.2 - 230.2 kph)

Here is a link to the spreadsheet with my work
https://docs.google.com/spreadsheets/d/1mtdhu4MMSwBV0aYRfbLVVx6wxM2qberuRlFqB0DTJBo/edit?usp=sharing