If after an investigation of the project grade line, it is found that the critical length of
grade must be exceeded, an analysis of the effect of the long grades on the level of service
of the roadway should be made. Where speeds resulting from trucks climbing up long
grades are calculated to fall within the range of service level D or lower, consideration
should be given to constructing added uphill lanes on critical lengths of grade. Refer to the
“Highway Capacity Manual” (Ref. 10) for methodology in determining level of service.
Where the length of added lanes needed to preserve the recommended level of service on
sections with long grades exceeds 10 percent of the total distance between major termini,
consideration should be given to the ultimate construction of a divided multilane facility.