Changing a line for my train

Hey,
I’ve been making a trainkit using physics, and I’ve stumbled on a problem. The problem is that whenever I hold down the “R” key and let go, the throttle sits at that which is what I want to change.

What I want to achieve is that when a user hits R the train should start to roll on the tracks and going up makes it faster.

ThrottleValue = math.clamp((1-Deltatime) * Current + (Deltatime * Goal), 0, MaxThrottle)

The line above is making it so that when you hit the key it goes up and when you release it stays on that number.

What can I change to make it so it continues so speed up when only pressed once?

here is the relevant code for this:

local ThrottleDirection = train.Important.Throttle.Value or 0
local ThrottleValue = train.Important.Current.Value or 0
local MaxThrottle = 100
local ThrottleIncPerSecond = 20 -- 4 seconds to get to 100.

-- inside the update function
	ThrottleDirection = (KeysDown.LShift and 1 or 0) + (KeysDown.LCtrl and -1 or 0)
	local Current = ThrottleValue; -- hold our current state
	local Goal = Current + (ThrottleIncPerSecond * ThrottleDirection)
	ThrottleValue = math.clamp((1-Deltatime) * Current + (Deltatime * Goal), 0, MaxThrottle)

thanks.