DESIGN MEMORANDUM NO. 8-98

TO:                                           Chief District Engineers
                                                  Active Consultants
                                                  Design Engineers

FROM:                                     John B. Sacksteder, P.E.
                                                  Director, Division of Highway Design

DATE:                                      February 3, 1999

SUBJECT:                               Geometric Design Criteria
                                                  English Update

In follow-up to Design Memorandum 11-98, the Geometric Design Criteria have now been updated in English units to meet criteria established in the 1994 AASHTO "A Policy on Geometric Design of Highways and Streets," otherwise known as the Green Book. As you are aware, this publication is written entirely in metric terms. Therefore the criteria established in this memo’s attachments are based on the Department’s best translation of the charts and equations contained in the Green Book with conversion to more rounded, English acceptable numbers.

Lane and shoulder widths have been retained as shown in the older, pre-1994 Geometric Criteria. However the radii and sight distance requirements have many revisions. Some revisions have also occurred in the maximum grade permitted.

The metric Geometric Design Criteria, contained in the current Design Manual, may continue to be used for those projects already developed in metric terms and intended to be let to construction with the metric usage. The Design Manual is currently being updated in accordance with our directives to convert back to English. More detailed information on such items as the superelevation charts will be included in the manual update.

Any questions regarding this memo or our shift back to English should be directed to this office.

JBS:jad

Attachment

GeDesCri.doc (Microsoft Word 97 Document)