9.1.3A Design Exceptions Form
FHWA Controlling Criteria
The following chart summarizes the ten FHWA controlling criteria with typical sources for the specific values. Actual values depend on the design standard chosen. Use this information to fill out the Highway Design Standards form.
GB designates the AASHTO Green Book (2011 version). NPS indicates the Park Road Standards. For NPS roads only use the Park Road Standards for the Design Speed, Lane Width, and Shoulder Width criteria. Use the AASHTO Green Book or applicable state or local standards for other criteria. (The standard values shown in the Park Road Standards are based on the 1984 Green Book and so are outdated).
A "High Speed" road is defined as having speeds greater than or equal to 50 mph [80 km/h] or a freeway. Note that only two controlling criteria apply for non-High Speed roads.
|Criteria||High Speed Only||Source||Explanation|
|Design Speed||GB Tables 5-1 & 6-1 & Section 7.2; NPS Table 1||Minimum design speed met based on the functional classification|
|Lane Width||✔||GB Tables 5-5, 6-5, 7-3; NPS Table 10||Minimum lane width achieved based on functional classification and chosen design speed|
|Shoulder Width||✔||GB Tables 5-5, 6-5, 7-3; NPS Table 10||Minimum shoulder width achieved based on functional classification and chosen design speed|
|Horizontal Curve Radius||✔||GB Table 3-7||Minimum horizontal curve radius achieved based on chosen design speed and maximum superelevation rate|
|Superelevation Rate||✔||GB Table 3-8 to 3-12||Was the correct superelevation rate chosen for each curve? Identify curves with insufficient superelevation.|
|Stopping Sight Distance||✔||GB Tables 3-1, 3-2, 3-34||Is stopping sight distance available along the horizontal alignment and for crest vertical curves? Use k values to assist calculation.|
|Maximum Grade||✔||GB Tables 5-2, 6-2, 7-2||Are all grades below the maximum grade?|
|Cross Slope||✔||GB Table 4-1||Selected cross slope falls within the appropriate standard range|
|Vertical Clearance||✔||GB Section 5.2.3, 6.2.3, 7.2.5||Minimum value achieved|
|Design Loading Structural Capacity||GB Section 5.2.3, 6.2.3, 7.2.5||Is structural capacity achieved|