Roadway Design Manual: Frontage Roads

Section 4: Frontage Roads

Overview

Table 4-4 and Table 4-5 show geometric design guidelines for 3R projects on rural and urban freeway frontage roads. These guidelines are acceptable for those projects involving either rehabilitation of only the frontage road or rehabilitation of the frontage road in conjunction with rehabilitation of the freeway mainlanes. 3R frontage road design guidelines should not be used when a freeway section is reconstructed from right-of-way line to right-of-way line, even though no additional frontage road lanes are added. Complete frontage road reconstruction projects should reference the applicable reconstruction guidelines for the appropriate criteria.

Frontage roads are built in some locations initially in a phased construction sequence with mainlanes to be built when traffic conditions warrant. If the frontage road is serving as the principal roadway pending future mainlane construction, apply the 3R design guidelines for rural multilane highways for rehabilitation work on these facilities.

Anchor: #CHDEFAADTable 4-4: 3R Design Guidelines for Rural Frontage Roads¹
Design Element	Guideline for Current ADT
Design Element	0 - 1,499		1500 or more
Design Speed (mph)	30		40
Lane Width (ft)	10		11
Shoulder Width (ft) Two-Way Operation	1		3
Inside Shoulder Width (ft) One-Way Operation	1		2
Outside Shoulder Width (ft) One-Way Operation	1		4
Clear Zone (ft)	7³		16
Bridges²: Width to be retained(ft)	24	24⁴
Notes: These values are intended for use on rehabilitation projects. However, the designer may select higher values to provide consistency with adjoining roadway sections, to provide consistency with prevailing conditions on similar roadways in the area, or to provide operational improvements at specific locations. Where structures are to be modified, bridges should meet approach roadway width as a minimum. (Approach roadway width is the total width of the lanes and shoulders.) Greater bridge widths may be appropriate if the rehabilitation project increases roadway life significantly or if higher design values are selected for the remainder of the project. Existing structure widths less than those shown may be retained if the total lane width is not reduced across or near the structure. For high-speed design (50-mph or greater), minimum clear zone is 16-ft. For current ADT exceeding 2,000, minimum width of bridge to be retained is 28-ft.

Anchor: #CHDHHEEJTable 4-5: 3R Design Guidelines for Urban Frontage Roads¹
Design Element	Guideline for All Traffic Volumes
Design Speed (mph)	30
Lane Width (ft)	10
Shoulder Width² (ft)	0 inside 2 outside
Clear Zone (ft)	Back of curb or outside edge of shoulder
Curb Offset (ft)	1 either side
Bridges: Width to be retained (ft)	Approach roadway not including shoulders
Notes: These values are intended for use on rehabilitation projects. However, the designer may select higher values to provide consistency with adjoining roadway sections, to provide consistency with prevailing conditions on similar roadways in the area, or to provide operational improvements at specific locations. For uncurbed shoulder widths see Table 4-4.