See Design 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.
– From ITE/CNU Fact Sheet 3 Design Factors to Control Speed *
* References soon to be out of date design controls
“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.”
– From AASHTO Guide for the Planning, Design, and Operation of Pedestrian Facilities
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.
– From USLimits2 – A tool to aid Practitioners in Determining Appropriate Speed Limit Recommendations
USLIMITS is a web based tool designed to help practitioners set reasonable, safe, and consistent speed limits for specific segments of roads. USLIMITS is applicable to all types of roads ranging from rural local roads and residential streets to urban freeways.
User-friendly, logical, and objective, USLIMITS2 is of particular benefit to local communities and agencies without ready access to engineers experienced in conducting speed studies for setting appropriate speed limits. For experienced engineers, USLIMITS2 can provide an objective second opinion and increase confidence in speed limit setting decisions.
– From FHWA USLIMITS2 A Web-Based Tool for Setting Appropriate Speed Limits
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:
– From ITE/CNU Fact Sheet 3 Design Factors to Control Speed
Factors Influencing Operating Speeds and Safety on Rural and Suburban Roads
This report provides information and background to transportation agencies and professionals so that they can apply the most appropriate technical knowledge about quantitative safety performance—crashes, their outcomes, and causal factors—to develop projects for a range of highway, street types and contexts. With such input, professionals can compare and contrast safety data with other measurable data about the environment, costs, traffic operations, and other factors, and they can make fully informed decisions.
Of particular interest to CSS practitioners, 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:
Roundabouts, curb bulb-outs, and speed humps are all forms of traffic calming, which offer promise if properly applied to curb speeding and some forms of aggressive driving. Pedestrians especially benefit from traffic calming. Traffic calming employs physical changes to the roadway, signage or operation changes, and can be thought of as a “silent policeman” enforcing speed limits where no law enforcement are present.
The Federal Highway Administration has financially supported the Institute of Transportation Engineers to develop a Traffic Calming Website in the interest of information exchange.
Within the traffic calming website:
See the NACTO Urban Street Design Guide for more information about:
Costs and Benefits of a Road Diet Conversion
FHWA Boost Safety by Going on a Road Diet
FHWA Signalized Intersections: An Informational Guide
