Sample Size (N) Determination for Speed Studies
		N =	S2 x z2 (2 + U2)
			2 x E2
	Souce
	Iterate if necessary	S =	Estimated Sample Standard Deviation (Start with 5.3 mph)
	Table 2.6 in Book	z =	Standard Normal Deviate = 1.96 for 95% Confidence
	Table 2.7 in Book	U =	Constant = 1.04 (for 85th% Speed)
	Usually between 1 and 5 mph	E =	Permitted Error (Start with 3.0 mph)
		N =	5.32 x 1.962 (2 + 1.042)		=	18
			2 x 3.02
We collect 40 speeds to be safe and then calculate the true sample standard deviation
Let's say the result is 6.7 mph.  Since 6.7 > 5.3, we must recalculate N
		N =	6.72 x 1.962 (2 + 1.042)		=	30
			2 x 3.02
Since 30 < 40 we can stop and calculate speed summary information (mean, 85th%, etc.)
Jeffrey Buckholz, P.E. - University of North Florida - TTE 4004