Safe Speeds

High vehicle speeds increase risk and the likelihood of crashes occurring and also increase crash severity. Crashes are more likely to result because higher speeds reduce the amount of time available to drivers to perceive and react to risky situations. They also increase braking distances, tire grip on the pavement may be affected, and there is an increased risk of loss of control. Additionally, at higher speeds drivers have a narrower field of vision so they are less likely to identify hazards or anticipate potential conflicts.

Research clearly demonstrates that higher speeds increase crash risk. The Insurance Institute for Highway Safety (IIHS) reports that a 5 mph (8 km/h) increase in the maximum speed limit was associated with an 8% increase in the fatality rate on interstates and freeways, and a 3% increase in fatalities on other roads.¹ Another study on speeds and safety revealed a 10% reduction in average speed resulted in 19% fewer injury crashes, 27% fewer severe crashes, and 34% fewer fatal crashes.²

Outcomes are more severe due to the increased forces involved at higher speeds. On average, a person struck by a car traveling at 40 mph (65 km/h) is five times more likely to be killed than a person hit by a car traveling at 20 mph (32 km/h).³ Outcomes are more severe for older pedestrians who are generally frailer, and also those struck by larger vehicles.

Safe speeds mean that drivers are travelling at a speed that is appropriate for the road conditions and road design, ensuring that evasive actions can be taken to avoid a crash and the likelihood of serious injury or fatality in the event of a crash is low. The conditions which determine safe speeds include factors such as weather, road surface conditions, visibility, presence of active transportation users, sight distances, presence of driveways and intersections, and roadside conditions.

The necessity of ensuring safe speeds through various measures can be illustrated through James Reason’s Swiss cheese model of crash causation. This model suggests that crashes occur from multiple system failures. For speeding-related crashes, a crash occurs when engineering controls in place fail (e.g., road design does not constrain a driver to travel at intended speed), administrative controls fail (e.g., inappropriate posted speed limit), and behavioural controls fail (e.g., enforcement presence insufficient to prevent speeding). When all three controls fail a hazard may result in a crash. The severity of the crash will also be influenced by mitigating factors (or barriers), such as the type of safety equipment in a vehicle.

The Swiss Cheese Model, James Reason 1990

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A Speed Management Program addresses undesirable speeds at individual locations, within corridors, or within broader areas. Achieving Safe Speeds requires the consideration of the context of each location in setting speed limits. However, it requires more than just posting appropriate speed limits to be effective. The program should address engineering, enforcement and educational measures.

Engineering relates to:

• Establishing speed limits appropriate for the primary purpose of the road

• Designing roads that induce drivers to drive at the desired speed through:

• • Lane widths

  • Allowing parking

  • Road diets

  • Raised medians

  • Roundabouts

• Providing traffic control devices to influence speed:

• • Advisory speed signs and pavement markings

  • Speed activated feedback signs

  • Optical speed bars

  • Controlled pedestrian crossings

• Providing traffic calming measures:

• • Speed humps

  • Speed tables

  • Mini roundabouts/traffic circles

  • Centerline hardening

• Gateway treatments for entries to rural villages and towns

Enforcement relates to:

• Establishing appropriate and effective penalties for speeding

• Establishing focus areas such as school and community safety zones

• Traditional speed enforcement by an officer using radar, laser or pacing approaches

• Automated speed enforcement

Education relates to:

• Providing information to the public about travel speeds and safety issues associated with speeding and to raise awareness of enforcement measures in effect

• Partnering with community organizations to develop and implement communication strategies around speeding

• Engaging law enforcement, engineering, public health, hospitals, news organizations (newspaper, radio, and/or TV), major employers, local businesses and other stakeholders

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Several agencies should be considered as stakeholders when developing a speed management program:

• Law enforcement

• Local engineering department

• Public works department

• Provincial/State department of transportation

• Elected officials

• Community groups

Engagement may be facilitated through a Speed Management working group that will help ensure a long-term commitment and to implement the plan. Elected officials can encourage agencies to participate, advance needed policy requirements, and obtain required funding. It is important that all engaged stakeholders understand their role in implementation of the program.

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The required data for a Speed Management program support a 4-step process:

• Step 1: Identify speeding issues

• Step 2: Identify appropriate countermeasures

• Step 3: Implement countermeasures

• Step 4: Evaluate projects and/or programs

Speeding issues may be identified through a combination of resources, including:

• Crash records

• Speed measurement programs

• Speeding citation history

• Skid marks on roadway

• Knocked down signs or guardrail/fencing strikes

• Partner agencies

• Citizen concerns

Other data are related to identifying appropriate countermeasures, including:

• Land use type (e.g., high density, low density, hamlet, or rural).

• Frequency of roadside access (e.g., number of residential and commercial driveways, intersecting roads).

• Road function (e.g., traffic movement versus access to abutting properties).

• Facility characteristics (e.g., paved width, divided or undivided, lane width and number of lanes, sight restrictions).

• Current vehicle speed data (e.g., data from a speed study).

• Existing speed limits.

• Special conditions that may exist (e.g., adverse alignment, the presence of pedestrians and cyclists, roadside design, high crash rates).

• Opportunities for high speeds

An evaluation of project and program success should primarily rely on:

• Before and after crash data

• Before and after speed data

• Before and after citation data

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There are various approaches for conducting a speed study and links to several tools are provided in this module. In general, the following tasks are involved:

1. Establish the study area

2. Assess the speed profile of the study area

   1. Collect vehicle speed data

   2. Compare locations to identify areas with high rates of speeding

3. Document the characteristics of the study area

   1. Traffic volume

   2. Speed limit in study area and adjacent roadways

   3. Physical characteristics of the road

   4. Adjacent land use

   5. Planning context

   6. Driveway spacing

   7. Pedestrian activity

   8. Collision frequency and severity

4. Document active transportation infrastructure

5. Determine root source of the speed issue

Whichever methodology is applied, the principle is to analyze speeds in the context of activity levels and other contextual factors, to determine the speed limit that will best minimize the risk of a person being killed or seriously injured. Generally, areas with high activity require lower speed limits since the risk of a crash is high, while somewhat higher speeds can be tolerated on streets with low activity. Roadways with limited sight distances also require lower speed limits.

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Rural towns and villages have an issue when drivers approach from a higher-speed rural road. Gateway treatments can be used to alert drivers in advance that the nature of the roadway will be suddenly changing and that they need to significantly reduce their speed. Gateway treatments can be a combination of traditional and non-traditional traffic control treatments. For example, enhanced signing, lane reductions, colored pavements, pavement markings, experimental striping, gateway structures, and traditional traffic calming techniques.

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In addition to lower crash risks, driving at lower speeds has other benefits. Since more fuel is required when vehicles travel at higher speeds, there are fuel and greenhouse gas emission savings associated with slower speeds. Concerning the optimum fuel-efficient travel speed for an average vehicle, fuel consumption per distance travelled at a slower speed starts with a high consumption rate and then decreases as average speed increases, up to approximately 80 km/h, then escalates with increasing speed.

Another benefit of vehicles travelling at lower speeds is an increased sense of security for active transportation users as well as reduced noise. More favourable conditions serve to encourage the use of active modes of transportation.

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There are several sources of information and tools related to ensuring safe speeds.

1. TAC Canadian Guidelines for Establishing Posted Speed Limits
This publication offers recommendations to help engineers and traffic practitioners determine speed limit management procedures, which enhance the effectiveness and credibility of posted speed limits. The guidelines provide an evaluation tool to assess appropriate posted speed limits based on the classification, function and physical characteristics of a roadway. It is an objective assessment based on engineering factors. The risks associated with the engineering factors determine the appropriate posted speed limit. The higher the level of risk, the lower the recommended posted speed limit. The application of the methodology determines posted speed limits, consistent with the roadway’s physical characteristics.  An automated spreadsheet is provided to facilitate the evaluation of posted speed limits.

2. FHWA Safe Speed Management Guide
This guide addresses managing speed to improve safety in terms of identifying roadways with speeding issues; diagnosing concerns and identifying appropriate engineering, enforcement, and education countermeasures; and implementing the selected countermeasures. The guide primarily focuses on local rural roads; however, many of the procedures and processes can be applied to other urban or State-owned facilities.

3. USLIMITS2 tool
USLIMITS2 is a web-based tool designed to help practitioners set reasonable, safe, and consistent speed limits for specific segments of roads. The tool is applicable to all types of roads; however, it is not applicable to school zones or construction zones. 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. Factors considered include: operating speed (50th and 85th percentile), annual average daily traffic, roadway characteristics and geometric conditions, level of development in the area around the road, crash and injury rates, presence of on-street parking, and extent of ped/bike activity, as well as several others depending on the road type. 

4. FHWA Speed Management website
The website presents facts and statistics, research, information and links related to Speed Management and Traffic Calming.

5. NACTO Setting Safe Speeds on Urban Streets
NACTO’s guidance gives practitioners a detailed, context-sensitive method to set safe speed limits on urban streets. Using the safe systems approach, City Limits provides a consistent, rational, scalable approach to urban speed limit setting, from citywide strategies to corridor-by-corridor methods based on easy-to-study street characteristics. City Limits outlines a three-method approach to speed limit setting that provides an alternative to percentile-based speed limit setting:

1. Setting default speed limits on many streets at once (such as 25 mph on all major streets and 20 mph on all minor streets),

2. Designating slow zones in sensitive areas, and

3. 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.

6. World Bank Global Road Safety Facility – Speed Management Hub
In this platform, the GRSF team provides evidence-based road safety knowledge to help manage speed through infrastructure interventions, effective enforcement, targeted awareness measures, and vehicle technology.

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