Setting speed limits that are safe, consistent, and reasonable is the first step in speed 

management and is important in order to protect all roadway users. Transportation 

practitioners employ a variety of strategies to manage speeds on roadways, and 

speed limits are an integral part of this. However, simply lowering the speed limit on a 

particular stretch of roadway does not always lower the actual speed at which most people 

drive on that roadway. Therefore, transportation agencies often install speed management 

countermeasures in order to get drivers to slow down.

WHAT DO SPEED MANAGEMENT COUNTERMEASURES 

LOOK LIKE?

Some speed management countermeasures are 

familiar to drivers and have been used for many 

years. Others are relatively new. All provide great 

safety and speed management benefits, and may 

offer operations and cost-savings benefits as well.

Some examples include:

 Speed Humps. Generally located on 

residential streets or other low-speed roads, these raised pavement structures force 

motorists to slow down to a safe speed. Studies show speed humps can be effective at 

reducing speeds by nearly 10 mph.1 (See page 2 to learn the difference between speed 

humps and speed bumps.)

 Speed Feedback Signs. These portable, interactive signs display a vehicle’s current 

speed to remind the driver to slow down and obey the posted speed limit. Research 

shows these types of signs have been effective at reducing speeds by 5 mph.2

Enhanced Curve Delineation. By improving striping or signing along horizontal 

curves, motorists are more aware of the road’s curvature and are more likely to slow 

down to a speed that matches the curve’s perceived severity. Depending on the type 

and combination of delineation countermeasures chosen, studies show speeds can be 

reduced by nearly 10 mph.3

Roundabouts. This type of circular intersection is very effective at safely moving traffic 

through an intersection and can have significant traffic calming effects. Features such as 

channelized approaches, a center island, and circular design encourage lower speeds. 

Studies have shown roundabouts can lower speeds by as much as 15 to 20 mph4 and 

reduce severe crashes by nearly 80 percent.5

Road Diets. The most common Road Diet converts a four-lane undivided roadway to a 

three-lane roadway consisting of two through lanes and a center two-way left-turn lane. 

Studies show that Road Diets, when implemented in appropriate contexts, can lower 

the 85th percentile speeds and greatly reduce the number of motorists 

speeding excessively.6

1, 2, 3, 4 FHWA, “A Desktop Reference of Potential Effectiveness in Reducing Speed,” July 2014. Available at: http://safety.fhwa.dot.gov/speedmgt/

ref_mats/eng_count/2014/reducing_speed.cfm.

5 FHWA, “Proven Safety Countermeasures - Roundabouts,” FHWA-SA-12-005 (Washington, DC: 2012). Available at: http://safety.fhwa.dot.gov/

provencountermeasures/fhwa_sa_12_005.cfm.

6 FHWA, Road Diet Informational Guide, FHWA-SA-14-028. Available at: http://safety.fhwa.dot.gov/road_diets/info_guide/.

More than Just Speed Humps

SPEED MANAGEMENT 

COUNTERMEASURES

COUNTERMEASURE:

Any intentional, long-term 

alteration to the roadway 

or its environment that 

causes changes in motorists’ 

driving behavior.

YOUR

YOUR

YOUR

YOUR

CURVE DELINEATION

SPEED FEEDBACK SIGN

ROAD DIET

ROUNDABOUT
http://safety.fhwa.dot.gov

CHOOSING A SPEED MANAGEMENT COUNTERMEASURE

Many agencies have traffic calming manuals or speed management policies that outline and guide their decisions on choosing 

speed management countermeasures. Transportation practitioners consider a variety of factors when selecting these 

countermeasures, which can be loosely grouped into the following categories.

Speed Hump vs. Speed Bump - both are used to control traffic speeds

 A speed hump is a gradual raised area on low-speed 

roadways, typically found on residential or local streets. 

 A speed bump is an abrupt raised area generally located 

in private driveways or parking lots. 

D

P

SPEED

HUMP

SPEED

BUMP

SPEED

HUMP

Speed limits frame expectations for drivers and other roadway users. Properly set speed limits provide a safe, consistent, and 

reasonable speed to protect drivers, pedestrians, and bicyclists along the roadway. At the same time, speed limits can be a source 

of frustration and confusion, for example, not all drivers like to travel at the same speed, and some people may not understand why 

the speed limit changes on a particular road. In addition, community residents often have concerns that traffic is moving too fast through 

their neighborhoods. Understanding the engineering principles and processes used to set speed limits and learning the terminology used 

to describe them are the first steps in reducing drivers’ frustration or confusion and encouraging compliance. 

TYPES OF SPEED LIMITS

STATUTORY SPEED LIMITS

Statutory speed limits are established by State legislatures for 

specific types of roads (e.g., Interstates, rural highways, urban streets) 

and can vary from State to State. They are enforceable by law and 

are applicable even if the speed limit sign is not posted. Examples of 

statutory speed limits include:

 25 mph in residential or school districts,

 55 mph on rural highways, and 

 70 mph on rural Interstate highways. 

POSTED SPEED LIMIT

Posted speed limits (sometimes called regulatory speed limits) are 

those that are signposted along the road and are enforceable by 

law. Some cities and counties will establish a blanket speed limit 

for roads in their jurisdictions. Those limits are generally posted at 

the city limits or county lines. A posted speed limit could be the 

same as the statutory speed set by the State legislature, or it could 

be established by a city, county, or State transportation agency as 

an adjustment to the statutory speed limit. The posted speed limit 

can differ from the statutory speed limit; in these cases, the posted 

speed limit is determined using an engineering speed study and 

takes priority over the established statutory speed limit.

“SPECIAL CONDITIONS” SPEED LIMITS

School zone speed limits are used in specific locations during the 

hours when children are going to and from school. Most States use a 

school zone speed limit of 15 to 25 mph in urban and suburban areas. 

Work zone speed limits are set as part of the work zone’s traffic 

control plan, which is used to help facilitate safe and efficient 

movement of traffic through a work zone. Factors that influence 

work zone speed limits can include:

 The posted speed limit when the work zone is not present,

 The location of the work zone and workers, in relation to traffic,

 The type of traffic control (e.g., cones, barrels, concrete barriers), and

 The complexity of the work zone (e.g., lane shifts, narrowed lanes).

Variable speed limits are displayed on changeable message signs 

(CMS) at locations where roadway conditions regularly require speeds 

to reduce more than 10 mph below the posted speed limit. These 

instances typically occur due to weather conditions, congestion, 

traffic incidents, and/or work zones.

Advisory speeds are a non-regulatory speed posted for a small 

portion or isolated section of a roadway (e.g., a sharp curve, an exit 

ramp) to inform a driver of a safe driving speed. They are set using 

an engineering speed study and in accordance with guidance in the 

Manual on Uniform Traffic Control Devices for Streets and Highways 

(MUTCD).

Basics

STATUTORY POSTED SCHOOL ZONE WORKZONE VARIABLE ADVISORY

SCHOOL

7:30-8:30 AM

2:30-3:30 PM

WORK

ZONE

SPEED LIMIT

FHWA-SA-16-077

Roadway Setting (i.e., Urban vs. Rural)

Most countermeasures are versatile and can be applied in a 

variety of locations, but some countermeasures may be more 

appropriate in either a rural or urban setting. For example, an 

urban neighborhood may not welcome the idea of rumble 

strips due to the additional noise, but rumble strips are 

appropriate and effective on a rural highway.

Roadway Type

Whether a roadway is an interstate, a freeway, or a city street 

influences the type of countermeasures that practitioners select. 

For instance, speed humps are not appropriate for a higherspeed roadway, but are well suited for streets with speed limits 

below 35 mph.

Speeding-related Crash History 

Transportation agencies often choose speed management 

countermeasures based on where, when, and what type of 

crashes are occurring. For example, curve delineation and 

rumble strips are effective countermeasures when a roadway 

is experiencing many speeding-related run-off-the-road 

crashes, and improving the visibility of intersections or 

installing roundabouts may reduce speeding-related 

intersection crashes.

Road Users

Practitioners also consider the users of the roadway and its 

surrounding area. For example, Road Diets are very effective at 

reducing speeds and allow designers to incorporate features 

such as bicycle lanes, pedestrian refuge islands, parking 

spaces, and wider sidewalks to accommodate the needs of all 

road users. 

Cost

Budget limitations can affect countermeasure selection. 

Agencies allocate their resources to achieve the best safety 

benefits with their available funding. Practitioners evaluate 

multiple alternatives to determine the solution that provides the 

best result for a specific location or for the system as a whole.

Effectiveness

Agencies carefully monitor studies that examine the effectiveness 

of speed management countermeasures in order to select the 

best solutions. The CMF Clearinghouse is an online resource 

practitioners can use to gather information on these studies 

and countermeasure effectiveness. FHWA’s Proven Safety 

Countermeasures website provides information on safety 

countermeasures that can be used for speed management 

such as Road Diets, medians, rumble strips, and roundabouts.

FOR MORE INFORMATION

To learn more about speed 

management, visit FHWA’s

Speed Management Safety 

web page.

For more information on speed 

limits, check out FHWA’s Speed Limit 

Basics fact sheet.