Traffic calming

Roadway geometries, vehicle type and traffic flow characteristics are factors commonly referred to in discussions of freeway capacity, primarily because they are significant and can be influenced by the application of traffic engineering techniques. There is another factor, or rather group of related factors, that can be classified under the broad term "weather," which have often been ignored in the sense of quantitative studies, although traffic engineers and motorists alike have cursed and praised many a day's weather. One reason weather factors have been largely neglected is chat they are, unlike geometries, not directly in the control of engineers. They also are discontinuous and therefore difficult to plan on or respond to - after all, if there was always two inches of snow on the pavement, or if it continually rained, we could make adjustments. As it is, one common reaction to bad weather is simple despair. Recently, attention has been paid to flexible traffic management techniques which, although still not putting engineers in control of the weather, allow management personnel to at least positively respond to weather conditions. An example of such flexible traffic management is the use of a metered freeway system, such as that along I-35W south of Minneapolis in Minnesota. Although it cannot hold off a snowstorm, such a system allows the input to the freeway to be controlled so that the reduced capacity is not exceeded and the accidents connected with bad weather are avoided. The question which management personnel must answer to respond appropriately to a particular weather situation is, "given this much rain (or snow or wind) how much will traffic flow be affected; that is, how severe should my response be?" Unless system operators know to what extent a particular situation threatens to reduce traffic flow, they can not respond confidently and appropriately. Because flexible traffic management is becoming increasingly common as a way to maximize the use of highway facilities when energy costs are high and construction dollars dwindling, it is time to take a quantitative look at the impact of weather on freeway capacity.

This final report covers the first phase of a research project to evaluate the effectiveness of selected traffic calming implementations in Richfield, Minneapolis, and Bloomington. The project's first phase included the development of criteria for traffic calming applications and the application of those criteria to sites in the above three cities. As one way to involve citizens in selecting traffic calming options, researchers also completed a survey of residents in Richfield and Minneapolis. Researchers also calculated traffic volumes for Richfield. City engineers selected the following sites for the project: residential areas in Richfield and Bloomington and a crossing of Willow Street in Minneapolis, which connects the Greenway with Loring Park. Each city plans to use the following techniques: buildouts or "blisters" in Richfield, a raised and striped platform in Minneapolis, and a no-left-tum sign for peak hours in Bloomington. The report also includes a comprehensive annotated bibliography on traffic calming. This report is unpublished. 15 copies were produced and distributed.

This report details a project to study the relationship between highway design and human behavior as influenced by roadside environments. In a visualization phase, computer simulation modeled an actual segment of urban highway planned for reconstruction in Tofte, Minn. Using a driving simulator, project design team members test drove the highway reconstruction project and evaluated the planned elements. In an experimentation phase, researchers tested drivers' responses to different design scenarios to identify the architectural and aesthetic elements with the greatest potential for calming or slowing traffic. Results indicated that the visualization phase increased communication among project team members and state agencies, facilitated problem identification-resolution strategy development, and contributed to decision making concerning potential design options and design elements. Data also indicated that white pavement treatments produced desirable traffic calming effects. Analyses of drivers' speed patterns indicated a consistent speed profile, characterized by both decreases and increases in speed. The report concludes with recommendations for the expanded use of visualization in general, and the implementation of white pavement treatments in the target reconstruction project specifically. It also recommends further consideration of landscape architecture treatments

Traffic calming alters the appearance or geometry of a roadway in an attempt to reduce traffic volume and speeds. This report will assist engineers with the evaluation, implementation, and application processes as they relate to traffic calming. It provides a “toolbox” containing purpose, cost, pros and cons, and effectiveness of various applications, as well as specific examples of projects in Minnesota. The success of traffic calming often hinges on the approval of residents and business who will be directly affected. To ensure success, engineers must work with the public to first define the problem, explore options, and then work with the residents and any service providers to decide the best solution. Temporary devices should be installed whenever possible. It is also crucial that engineers consider the overall design plan, since traffic calming is often retrofitted to existing roadways. Engineers must also be sure to collect any before/after data, Average Daily Traffic (ADT), 85th percentile speed, and related information to better document the outcome of installing a traffic calming device.

This research examines the extent of traffic calming activity in Minnesota and the degree of actual and perceived success of such projects. Traffic calming activities, which range from traditional actions such as tum prohibitions and stop signs to changes in roadway width and appearance, have gained popularity as neighborhoods attempt to reduce traffic, reduce speeds, and create a safer and more attractive street environment. The research objectives included determining how widespread traffic calming activities have become in the state; determining whether implemented traffic calming strategies have achieved their purposes; and determining whether proposed design changes are compatible with local and state design standards, and--if they are not--to suggest guidelines for future applications. A comprehensive survey was sent to cities, counties, and agencies. Fifty-three percent responded and identified 67 projects, both implemented and planned. The great majority of respondents report satisfaction with project results. However, quantitative information--in the form of before-and-after data--in support of these results is limited. Perceived results, while positive, do not always reflect the achievement of the initial project objectives. A handful of projects are being considered for implementation on minor arterials, which are designed to carry higher volumes of traffic, at higher speeds, than neighborhood streets and collectors. It is on these roads, primarily, where the objectives of traffic calming can conflict with the function of the roadway and its design elements.

Annually, thousands of highway workers risk serious injury and death from drivers who enter work zones too fast or accelerate after entering the zone and then, because of their excess speed relative to the environmental limitations, have insufficient time to avoid accidents in the zone. Slow-moving vehicles are a problem in reducing traffic flow. This research investigated the effectiveness of a system of pulsing lights, that gave the illusion of movement (Phi phenomenon), in causing drivers to unknowingly synchronize their vehicle speed with the light pulses. Forty drivers participated: 20 young (10 female, 10 male; 21-42 years) and 20 older adults (10 female, 10 male; 55-87 years). Each participant made 15 passes through the work zone: a control pass with stationary white lights, two control passes with no lights, and 12 passes of test conditions -- 2 colors (red & green) x 3 apparent pulse speeds (-80, 0, & +80 mph) x 2 zone entry speeds (40 & 70 mph). Age, sex, and zone entry speed differences were found, but overall, (1) backward moving lights (-80 mph) caused drivers to reduce their vehicle speed, (2) forward moving lights (+80 mph) caused drivers to increase their vehicle speed, (3) stationary light and control lights had little or no effect, and (4) green produced stronger effects than red. Backward moving lights caused the greatest slowing in the young while forward moving lights caused the greatest acceleration in the old males and young females.

Minnesota statute provides for a wide range of school zone speed limits (SZSLs) from which local authorities may select. This Transportation Research Synthesis summarizes the current research regarding setting SZSLs, effective methods and procedures for setting school zone speed limits and known spillover or other unintended consequences for setting improper school zone speed limits to provide guidance on SZSL best practices. The majority of states use a statute to define a SZSL, with over half of these states having a statutory SZSL set at 15, 20 or 25 mph. Many allow jurisdictions to lower SZSLs further based on an engineering and traffic study. Minnesota statute allows for a larger range than any other state. Based on available research, SZSLs consistently reduce mean and 85th percentile speeds, however the extent of the reductions and statistical significance varies. In many cases, a SZSL resulted in lower compliance with speed limits, however, lower overall speeds and tightening and leftward shift of speed distributions indicate overall safety benefits. Crash histories through school zones overwhelmingly found reductions in crashes, in particular, reductions in fatal and serious injury crashes involving vulnerable roadway users. The speed differential between the approach speed limit and the SZSL has an impact on compliance and safety, with a recommended differential of 5 to 10 mph and speed buffer zones on high-speed roadways. The layering of additional countermeasures such as flashing beacons and geometric changes to the roadway are recommended as best practices to achieve lower speeds in school zones. No unintended consequences on vehicle speeds nor user safety were identified.