Planning and designing streets, corridors and networks so vehicle speed is appropriate to a given function and context. Topics include: Traffic Calming, Traffic Calming and Target Speed.
[The ITE-CNU guide] recommends replacing design speed with a “target speed.” A lower target speed is an essential characteristic of thoroughfares in walkable, mixed-use urban areas. Target speed is the highest speed at which vehicles should operate on a thoroughfare in a specific context, consistent with the level of multi-modal activity generated by adjacent land uses, to provide both mobility for motor vehicles and a safe environment for pedestrians, bicyclists, and public transit users. The target speed is intended to be used as the posted speed limit. In some jurisdictions, the speed limit is established based on measured speeds. In these cases, it is important for the design of the thoroughfare to encourage an actual operating speed that equals the target speed.
Source: Fact Sheet 3 Design Factors to Control Speed (ITE/CNU)
“The selected design speed should be appropriate for the specific street being designed, including consideration of the anticipated vehicle operating speeds and the anticipated level of pedestrian activity.”
Source: Guide for the Planning, Design, and Operation of Pedestrian Facilities (AASHTO)
Speed limits are selected to balance travel efficiency versus safety. It can be argued that a rational speed limit is one that is safe, that most people consider appropriate, that will protect the public, and can be enforced. Many practitioners also feel that better methods are needed to identify appropriate speed limits especially in urban roads having higher traffic volumes, a mix of road users, and more roadside activity. Many practitioners and researchers have argued that a knowledge-based expert system can provide assistance to the practitioner in setting the appropriate speed limit for specific conditions on a road section.
Source: USLimits2 (FHWA)
Design Factors That Influence Target Speed Establishing a target speed that is artificially low relative to the design of the thoroughfare will only result in operating speeds that are higher than desirable and that are difficult to enforce. The design of the thoroughfare should start with the selection of a target speed, which is then applied to geometric design elements. The following design factors contribute to speed reduction and should be incorporated into thoroughfare designs as appropriate in urban areas:
Source: Fact Sheet 3 Design Factors to Control Speed (ITE/CNU)
The Factors Influencing Operating Speeds and Safety on Rural and Suburban Roads report provides information on design details, safety effectiveness, speed reduction effectiveness and cost, for speed reduction techniques such as:
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