The game has evolved to where simple WALK/RUN is outmoded.
You're either WALKING (a set numeric movement rate) or RUNNING going at MAXIMUM movement rate.
What they really need is a slider that would represent a percetange of your maximum movement rate.
0-100% Slider with 10% increments
0% = WALK to 100% = fastest possible rate
This would address problems people are now having when navigating areas which were never intended for the speed at which people can now travel. I've seen at least a half-dozen guys fall to their death in Velks Lab because they had RunSpeed3 and just couldn't make the corners unless they were walking.