Rules of the Road

Maricopa County’s roadway network supports and encourages the movement of people and resources between destinations. To meet the needs of all roadway users, MCDOT relies on a combination of rules, regulations and public awareness to keep its roadways operating safely and efficiently.

  1. Speed Limits
  2. Roadway Maintenance
  3. Use of County RIGHT-OF-WAY

Speed Limits

The Maricopa County Department of Transportation (MCDOT) is responsible for planning, designing, building, maintaining and operating the County’s roadway network.  The Maricopa County Sheriff’s Office (MCSO) is responsible for enforcing the roadway regulations approved by the Board of Supervisors.

How speed limits are set

Speed limits are based on engineering studies.  These studies are conducted by MCDOT’s Traffic Studies Branch and take into consideration many factors which affect the safety and operations of a roadway. 

These factors include:

  • Roadway classification:  A roadway may be classified as a local residential street, collector road or major arterial roadway.
  • Roadway users:  People utilize roadways for many reasons including personal travel, truck routes, transit, pedestrians, bicycling, parking, driveway access and more.
  • Lanes and shoulders: The size of travel lanes and shoulders influences how vehicles and other roadway users utilize the roadway.
  • Alignment and sight distance:  Dips, curves, vegetation and other factors can affect how far ahead or behind a driver or other roadway user can see.
  • Current vehicle operating speeds: Engineers will conduct a speed study to determine how fast drivers are currently driving on the road.  This study will determine the 85th Percentile speed.  This is the speed at which 85 percent of all vehicles travel at or below.  Speed limits may be set at or below the 85th Percentile, depending on roadway conditions.
  • Reported crash history: Engineers will consider reported crashes on the roadway as well as what may have caused the crash, if known, and other safety factors.     

In addition to these factors, MCDOT strictly adheres to the guidance issued in the Manual on Uniform Traffic Control Devices (MUTCD) for setting speed limits.   The MUTCD is the national standard for signing on all highways. Sections 2B.13-16 address regulatory speed limits and Section 2C addresses advisory speed signs. School zone speed limit signs are discussed in Section 7B and work zone speed limits in Section 6C.

Placement of portable speed feedback signs

MCDOT utilizes portable speed feedback signs to inform drivers of their traveling speed and encourage them to obey posted speed limits.  

These signs use radar to detect the speed of oncoming traffic and display the approximate speed in real-time.  This allows drivers to compare their current rate of speed with the posted speed limit and make adjustments as necessary.

Due to the limited number of signs available for use by MCDOT, these portable speed feedback signs are prioritized for use in construction work zones and speed study locations throughout unincorporated Maricopa County.

Speed humps and traffic calming measures

MCDOT utilizes traffic calming measures, including speed humps to address excessive cut-through traffic on local roads. Roadways must meet the criteria of Maricopa County’s Traffic Calming Ordinance (P-29), which is confirmed through an engineering study and requires the support of residents, businesses and emergency responders in the area. Based on input from local emergency responders, MCDOT will not consider the installation of speed humps in the Sun City or Sun City West communities because they may increase emergency response times in situations where every minute counts.

The Maricopa County Traffic Calming ordinance allows for several types of traffic calming measures to be studied and, if found to be warranted, constructed.  These measures include:

  • Chicane: A combination of raised curb and striping to narrow lane width and reduce speed through on a local road.
  • Choker: The narrowing on one side or both sides of a local road in such a manner as to reduce speed without impairing safe two-way traffic.
  • Diverter: A barrier type device that forces traffic to make only a left turn or right turn at an intersection.  A diverter is normally used to control direction and flow of traffic in residential neighborhoods.
  • Speed hump/cushion: An asphalt hump, approximately 3.25 inches high and up to 12 feet in width running across the road.  The raised hump encourages drivers to reduce speeds while driving over them.
  • Traffic circle: A type of circular intersection, used primarily in low volume residential neighborhoods in which traffic must travel in one direction around a small central island. This encourages drivers to reduce speed while driving through neighborhoods.

Residents living on a County local road with a posted speed limit of less than 35 may request MCDOT study the feasibility of placing traffic calming devices on their street. 

To become eligible for traffic calming measures:

  • The speed criterion for consideration of traffic calming shall be an 85th percentile speed of at least 8 miles per hour over the posted speed limit, and the traffic volume criterion shall be at least 1,100 vehicles per day.
  • Additionally, 80% of property owners whose property is adjacent to the roadway segment must agree to traffic calming plans. 
  • Speed humps require the support of emergency responders in that area.

Residents can request more information about traffic calming through Notify MCDOT.

Speed Enforcement

The Maricopa County Sheriff’s Office is responsible for enforcing speed limits.  Questions regarding speed enforcement, including use of radar and cameras to enforce speed limits, should be directed to MCSO at (602) 876-1000.