Impact of Speed Limit Changes on Urban Streets

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Creator
Date Created
2023-06
Report Number
2023-22
Description
In 2019 the Minnesota Legislature amended that state’s statutes to allow cities to set speed limits on city-owned streets. In February 2021 we surveyed 33 cities within the Twin Cities metro area and identified the city of St. Louis Park as planning to implement a city-wide change in speed limits, with a default speed limit of 20 mph but with selected roads being signed for limits ranging from 25 mph to 35 mph. Speed data was collected using road tube traffic recorders in the summer of 2021, 2-4 months before the speed limit change, and in the summer of 2022, 6-8 months after the change. There was considerable variability regarding what was seen at individual locations, with before/after differences in mean speed ranging from a decrease of 7 mph to an increase of 2.4 mph. On average, mean speeds were slightly lower (1-2 mph) in the after period, both on streets where the speed limit was lowered and on streets where the limit was unchanged. This pattern, modest reductions in mean speeds following a reduction in speed limit, with possible spillover, was consistent with what has been seen in other cities in North America and Great Britain.

Synthesis of Speed Control Devices

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Date Created
1992-03
Report Number
RIS-10
Description
Vehicle speed control is a concern for many neighborhood residents as well as city and county engineers. Residents are concerned with vehicle speed for many reasons including: safety of their children and pets, property values, noise, visibility, and dust control. Engineers have tried numerous devices and strategies to control vehicle speed. Many solutions appear to be effective, however, upon further evaluation they are not. This, coupled with success from one type of speed control used at one location and with failure found using the same type in a different location, makes it difficult for engineers to decide which type of speed control will work best in their community. This report will review a questionnaire sent to all the Minnesota county and larger city engineers, examine some common types of speed control, and explore some new techniques which may add to speed control options.

Guidelines for Determining Speed Limits on Municipal Roadways

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Date Created
2023-04
Report Number
2023RIC07
Description
The issue of reducing speed limits to increase public safety is an emotional, political, and controversial topic that has been debated by safety advocates, engineers, politicians, transportation officials, and the public for many years. A recent statutory change has put a spotlight on the topic, necessitating a deeper look into how speed limits are established and the effectiveness that lowering speed limits has on reducing vehicle traveling speeds, as well as the impacts on pedestrian and bicycle traffic. This document examines the history of speed limits, the recent statutory change, and the consequence of the change to communities. In addition, it examines the effectiveness of speed limit changes and outlines a process for agencies to follow when deciding to make a change, and offers alternative strategies for pedestrian and bicycle safety.

Speed Safety Cameras (SSC) Transportation Research Synthesis

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Date Created
2023-02
Report Number
TRS2303
Description
Since the mid-1990s, the use of Speed Safety Cameras (SSCs), also referred to as Automated Speed Enforcement (ASE), as a speed reduction countermeasure has been growing across the US. Minnesota does not currently permit SSCs by law, but recent interest from community leaders has led to the reconsideration of the use of SSCs on Minnesota roadways. The purpose of this TRS is to review relevant research regarding the impact of SSCs as a standalone countermeasure to: reduce and manage speeds, to reduce the severity and frequency of crashes, and to understand spillover or other unintended consequences. Just over 150 communities and 20 states within the US are currently using SSC systems. Of the 13 methodologically sound SSC studies and four literature reviews that evaluated the effects of SSCs on driver speeds, all found some level of speed reductions for mean, threshold, and/or 85th percentile speeds. Of the eight SSC studies and six literature reviews that conducted multi-year crash history analysis before and after the implementation of SSC programs, all found reductions in the number of fatal and severe crashes. Of the studies that reported both overall crashes as well as serious and fatal crashes, all concluded that SSCs resulted in the greatest reductions for serious injury and fatal crashes. No increase in crash rates or other adverse safety effects were reported. Results are consistent with other literature reviews published from 2005 to 2010. The research indicates that SSCs are an effective countermeasure for reducing speeds, crash frequency and crash severity.

School Zone Speed Limits (SZLSs) Transportation Research Synthesis

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Date Created
2023-02
Report Number
TRS2301
Description
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.