9.1.3A Design Exceptions Form

The following information supplements PDDM Section 9.1.3.

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 (The standard values shown in the Park Road Standards are based on the 1984 Green Book and so are outdated).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

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