3.5 Speed, Mobility and Access Considerations

Issues associated with users should be considered to achieve a proper contextual design solution. Driver accommodation is one area that defines the context-roadway interaction for drivers considering target speed
and the balance between mobility
and access
.

3.5.1 Target Speed

The use of target speed for roadways recognizes the influence of driver desire and expectation. The target speed is the operating speed that the designer intends for the drivers to use. A goal of the expanded functional and context classification system is to develop a facility where the target speed is in the proximity of the design speed. The target speed should consider both existing and future volumes and contexts.

Section 4.2.4

provides additional guidance for the determination of target speed.

3.5.2 Mobility and Access

Mobility
is defined as function of congestion level:

Low: (congested conditions);

Medium: (some congestion); and

High: (no congestion; free flow).

Mobility levels are based on general concepts of the level of service (LOS) for a facility and correspond to broad values of all roadways.

Access
is defined as the frequency of driveways or intersections and are grouped into three categories based on distance between access points:

Low: (> 0.75 mile)

Medium: (0.75 – 0.25 mile)

High: (< 0.25 mile)

Definitions of mobility and access are derived from

NCHRP Web-Only Document 230: Developing an Expanded Functional Classification System for More Flexibility in Geometric Design

Table 3-5

shows how driver expectations change based on the different combinations of context and roadway functional classification. Refer to Chapter 1 of the

Access Management Manual

for additional information on this topic.

Table 3-5: Speed, Mobility, and Access Considerations
Functional Class	Context
Functional Class	Rural	Rural Town	Suburban	Urban	Urban Core
Freeway	Speed: High Mobility: High Access: Low	N/A	Speed: High Mobility: High Access: Low	Speed: High Mobility: High Access: Low	Speed: High Mobility: High Access: Low
Arterial	Speed: High Mobility: High Access: Med	Speed: Low/Med Mobility: Med Access: High	Speed: Med Mobility: Med Access: Med	Speed: Low/Med Mobility: Med Access: Med/High	Speed: Low Mobility: Med Access: Med/High
Collector	Speed: High/Med Mobility: Med Access: Med	Speed: Low Mobility: Med Access: High	Speed: Med Mobility: Med Access: High	Speed: Low Mobility: Med Access: High	Speed: Low Mobility: Med Access: High
Local	Speed: Med Mobility: Med Access: Med	Speed: Low Mobility: Med Access: High	Speed: Low Mobility: Low Access: High	Speed: Low Mobility: Low Access: High	Speed: Low Mobility: Low Access: High