Literature Review Matrix
A summary of research and literature related to speed limits.
The goal of the Minnesota Statewide Speed Limit Vision Project is to develop a consistent and unified message related to speed limits supported by cities, counties, special interests, public safety and enforcement. Various types of research efforts were conducted to gather the latest and most relevant information available. The literature review matrix summarizes, in chronological order, both state and nationwide publications of this relevant speed limit information.
See the table below or download the Literature Review Matrix (PDF).
|1993||The ITE Committee 4M-25 draft guidelines Recommended Practice||ITE Committee 4M-25||
|1998||Synthesis of Safety Research Related to Speed and Speed Management||FHWA|
|Past research has shown that the 85th percentile speed coincides with the lowest accident rates and reflects a safe speed for existing conditions as perceived by the majority of motorists. This research and approach are based on the Solomon Crash Risk Curve developed in the 1960s for rural highways. Solomon reported that the results of his study showed that “low speed drivers are more likely to be involved in accidents than relatively high speed drivers.”
This 1998 study concluded that “there is evidence that crash risk is lowest near the average speed of traffic and increases for vehicles traveling much faster or slower than average. In general, changing speed limits on low and moderate speed roads appears to have little or no effect on speed and thus little or no effect on crashes. This suggests that drivers travel at speeds they feel are reasonable and safe for the road and traffic regardless of the posted limit. However, there is limited evidence that suggests the net effect of speed limits may be positive on a system wide basis. More research is needed to evaluate the net safety effect of speed limit changes.”
|2007||Review of 20 mph zones in London Boroughs||Webster, D. and R. Layfield||A 2007 review of half of the 20 mph zones which had been implemented in London (78 zones) found that they reduced injury accidents by about 42% and fatal or serious accidents by 53%.|
|2007||USLIMITS2||FHWA and the National Cooperative Highway Research Program (NCHRP)||FHWA and NCHRP released USLIMITS2 to assist practitioners in setting speed limits that are safe, credible, consistent and enforceable. When used to determine appropriate speed limits, this web-based expert approach provided a systematic, consistent method for examining and weighing factors in addition to vehicle operating speeds.|
|2008||Study and Report on Speed Limits||MnDOT||Recommended some changes to the definition of Urban District, Rural Residential District, and Residential Roadway.
Recommended no change to the basic Urban District speed limit of 30 MPH based upon the following:
|2011||Impact Speed and a Pedestrian’s Risk of Severe Injury or Death||AAA Foundation for Traffic Safety||The study used data from a federal study of crashes that occurred in the United States in years 1994 – 1998 in which a pedestrian was struck by a forward‐moving car, light truck, van, or sport utility vehicle.
Results showed that the average risk of severe injury for a pedestrian struck by a vehicle reaches increases by vehicle speed.
|2012||NHTSA Summary of State Speed Laws, 12th Edition||National Highway Traffic Safety Administration (NHTSA)||States surrounding Minnesota all have a statutory speed limit of 25 MPH unless otherwise posted: Iowa, Wisconsin, North Dakota, South Dakota, and Nebraska. The most common speed limit in the U.S. for local city streets is 25 MPH.|
|2012||Methods and Practices for Setting Speed Limits: An Informational Report||Gerald Forbes as part of the Federal Highway Administration (FHWA) Safety Program||Four general methods for setting speed limits
Engineering, Expert Systems, and Optimization are generally used for adjusting speed limits on a street by street basis. The Safe System Approach is more commonly applied at the city, county or state level to adjust a state statutory speed limit across the board.
The 85th percentile speed or engineering approach is just one of the methods used in current practice, although it is the most common.
|2012||Methods and Practices for Setting Speed Limits (TRS 1204)||MnDOT||A synthesis of pertinent research to be used for further study. Focused on national resources, consultation with state practitioners, state practices, international practices, and related research.|
|2013||A Model for Setting Credible Speed Limits in Urban Area||Institute of Transportation Engineers (ITE) Journal||This article presents a new model for setting credible speed limits exclusively in urban areas by setting limits from 25 to 43 mph by increments of 6 mph. The model is based on research in Quebec, Canada. The model uses eight key parameters whose cumulative effects significantly affect the 85th percentile speeds, giving more weight to certain factors. Parameters include: number of lanes, width of visual clearance, length of zone, type of surroundings, access points, on-street parking occupancy, pavement width, and number of commercial buildings.|
|2015||Traffic Safety Fundamentals Handbook||MnDOT||Data showed the relationship between speed limit and average crash rates for urban highways on the State’s system. This data indicates that in Minnesota crash rates go down as speed limits increase along urban highways.
|2017||Evaluation of Bicycle Traffic Control Devices and Street Design Elements in Minneapolis||City of Minneapolis||This report documents the evaluation of 16 bicycle treatments and street design elements installed by Minneapolis Public Works in 2011 and 2013.
|2017||“Reducing Speeding Related Crashes Involving Passenger Vehicles”||National Transportation Safety Board (NTSB)||
|2018||“Studies Say Lower Speed Limits will Help Improve Road Safety”||American Association of State Highway and Transportation Officials (AASHTO) Journal||Documented the Insurance Institute for Highway Safety (IIHS) study on Boston, Massachusetts, which lowered the default speed limit on city streets from 30 mph to 25 mph beginning January 9, 2017, after the Massachusetts legislature amended state law in 2016 to allow cities and towns to lower speed limits from 30 mph to 25 mph on municipal roads in densely populated areas or business districts.
This study found that lowering the speed limit did lower the amount of speeding drivers going over 35 mph by up to 29%.
|2019||NCUTCD proposal for recommended changes to the MUTCD||National Committee on Uniform Traffic Control Devices (NCUTCD)|
Item No. 18B-RW-03
NCHRP 17-76 is due out in Fall 2020.
|2019||Current Speed Limit Legislation in Minnesota||2019 Minnesota Statute (MS) 169||No person shall drive a vehicle on a highway at a speed that is greater than is reasonable and prudent under the conditions. Statutory speed limits established by the legislature:
|2019||National Motorists Association website||National Motorist Association|| Ideally speed limits should be set at the 85th percentile speed and at a minimum should never be set below the 67th percentile free flow speed.
This is based on draft guidelines that were a result of the 1993 ITE Committee 4M-25 on Speed Zone Guidelines Recommended Practice.
|2019||Sustainable Speed Limits for Urban Streets||Op-Ed in the ITE Journal by Peter Martin, PE||The current practice for setting speed limits is being reviewed by the American Association of State Highway Officials, the National Committee on Uniform Traffic Control Devices, ITE, and others.
|2019||Minnesota Manual on Uniform Traffic Control Devices (MN MUTCD)||MnDOT||The 85th percentile speed or engineering approach is most common method as its described in the MUTCD.
The Minnesota Manual on Uniform Traffic Control Devices (MN MUTCD) Section 2B.13 Speed Limit Sign provides that “Speed zones (other than statutory speed limits) shall only be established on the basis of an engineering study that has been performed in accordance with traffic engineering practices. The engineering study shall include an analysis of the current speed distribution of free-flowing vehicles” (2B-14)
MN MUTCD Section 2B.13 Speed Limit Sign (R2-1) provides guidance that “when a speed limit within a speed zone is posted, it should be within 5 mph of the 85th-percentile speed of free-flowing traffic” (2B-15).
|2020||City Limits: Setting Safe Speed Limits on Urban Streets||National Association of City Transportation Officials (NACTO)||Developed by a steering committee of NACTO’s 86 member cities and transit agencies, City Limits outlines how to use a safe systems approach to set speed limits in urban environments, in contrast to traditional methods (e.g. the 85th percentile). City Limits outlines a three-method approach to speed limit setting that provides an alternative to percentile-based speed limit setting:
• Setting default speed limits on many streets at once (such as 25 mph on all major streets and 20 mph on all minor streets),
• Designating slow zones in sensitive areas, and
• Setting corridor speed limits on high priority major streets, using a safe speed study, which uses conflict density and activity level to set context-appropriate speed limits.
|2020||Effects of Residential Street Speed Limit Reduction from 25 to 20 mi/hr on Driving Speeds in Portland, Oregon: Final Report (pdf)||Portland State University - Civil & Environmental Engineering |
(report prepared for Portland Bureau of Transportation)
|Report analysis suggests the reduction of posted limits to 20 mph resulted in lower observed vehicle speeds and fewer vehicles traveling at higher speeds (e.g. over 30 mph). However while observed average speeds decreased at a majority of sites, they did increase at a few sites. Models also suggest the role of roadway characteristics such as width, pavement condition, and curb presence on vehicle operating speeds.
Article from Portland.gov website:
Analysis indicates 20 mph speed limit reduced driving speeds