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The two-lane rural highway version of the PRM contains 20 highway geometric design checks. Only 16 of these checks are available in the current release of IHSDM. Checks are organized into four categories: cross section, horizontal alignment, vertical alignment, and sight distance.
In the above list, asterisks denote elements included among the 13 controlling criteria established by FHWA in the Federal-Aid Policy Guide (Transmittal 23, dated June 17, 1998). PRM checks include 9 of the 13 controlling criteria. The controlling criteria that are not checked by the PRM are: design speed, structural capacity, vertical clearance, and horizontal clearance. The designation of elements as controlling criteria is relevant to projects covered by the Federal-Aid Policy Guide; this designation may not be relevant to other projects.
Section 4., Cross Section Checksthrough Section 7., Sight Distance Checks of the PRM Engineer's Manual describe the details of these components for each check. For each policy check, the engineer's manual provides the following information: overview of the check, input data requirements, the PRM process, boundary conditions and rounding, special conditions, and output. The inputs required to perform a check are listed in the input data requirements section. The PRM process section identifies the source of the policy values against which designs are checked and describes how the comparison between road and policy values is made. Policy tolerance values and rounding are detailed in the boundary conditions and rounding section. The special conditions section contains information about policy values for special cases addressed in AASHTO policies and describes how the PRM handles anomalies in the policy. Lastly, the output section describes the format of the output tables, detail about the road and policy values for a specific check, and a listing of output comments and a description of the situations they represent.
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