In the United States, speed limits are set by each state or territory. States have also allowed counties and municipalities to enact typically lower limits. Highway speed limits can range from an urban low of 25 mph (40 km/h) to a rural high of 85 mph (137 km/h). Speed limits are typically posted in increments of five miles per hour (8 km/h). Some states have lower limits for trucks, some also have night and/or minimum speed limits.
The highest speed limits are generally 70 mph (113 km/h) on the West Coast and the inland eastern states, 75–80 mph (121–129 km/h) in inland western states, along with Arkansas, Louisiana, Maine, and Michigan; and 65–70 mph (105–113 km/h) on the Eastern Seaboard. Alaska, Connecticut, Delaware, Massachusetts, New Jersey, New York,^{[1]} Puerto Rico, Rhode Island, and Vermont have a maximum limit of 65 mph (105 km/h), and Hawaii has a maximum limit of 60 mph (97 km/h). The District of Columbia and the U.S. Virgin Islands have a maximum speed limit of 55 mph (89 km/h). Guam and the Northern Mariana Islands have speed limits of 45 mph (72 km/h). American Samoa has a maximum speed limit of 30 mph (48 km/h).^{[2]} Two territories in the U.S. Minor Outlying Islands have their own speed limits: 40 mph (64 km/h) in Wake Island, and 15 mph (24 km/h) in Midway Atoll.^{[3]}^{[4]} Unusual for any state east of the Mississippi River, much of Interstate 95 (I95) in Maine north of Bangor allows up to 75 mph (121 km/h), and the same is true for up to 600 mi (966 km) of freeways in Michigan. Portions of the Idaho, Montana, Nevada, Oklahoma, South Dakota, Texas, Utah, and Wyoming road networks have 80 mph (129 km/h) posted limits. The highest posted speed limit in the country is 85 mph (137 km/h) and can be found only on Texas State Highway 130, a toll road that bypasses the Austin metropolitan area for longdistance traffic.
During World War II, the U.S. Office of Defense Transportation established a national 35 mph "Victory Speed Limit" (also known as "War Speed") to conserve gasoline and rubber for the American war effort,^{[5]} from May 1942 to August 1945, when the war ended. For 13 years (January 1974^{[6]}–April 1987^{[7]}^{[8]}), federal law withheld Federal highway trust funds to states that had speed limits above 55 mph (89 km/h).^{[7]} From April 1987 to December 8, 1995, an amended federal law allowed speed limits up to 65 mph (105 km/h) on rural Interstate and rural roads built to Interstate highway standards.
This table contains the most usual posted daytime speed limits, in miles per hour, on typical roads in each category. The values shown are not necessarily the fastest or slowest. They usually indicate, but not always, statutory speed limits. Some states and territories have lower truck speed limits applicable to heavy trucks. If present, they are usually only on freeways or other highspeed roadways. Washington allows for speeds up to 75 mph (121 km/h), but the highest posted signs are 70 mph (113 km/h). Mississippi allows speeds up to 80 mph (129 km/h) on toll roads, but no such roads exist.
Legend:  

Freeway: Interstate Highway or other state or U.S. Route built to Interstate standards. Divided rural: State or U.S. route, generally with four or more lanes, not built to Interstate standards, but with a median or other divider separating directions of travel. Undivided rural: County, State, or U.S. route, generally with two to four lanes, with no separator between directions of travel. Residential Street/residential: Residential streets, business districts, or School zones.  



Further information: Speed limits in the United States by jurisdiction 
State or territory  Freeway (rural)  Freeway (trucks)  Freeway (urban)  Minimum speed (freeways)  Divided (rural)  Undivided (rural)  Residential 

Alabama^{[9]}^{[10]}  70 mph (113 km/h)  50–70 mph (80–113 km/h)  None  65 mph (105 km/h)  55–65 mph (89–105 km/h)  20–25 mph (32–40 km/h)  
Alaska  65 mph (105 km/h)  55–65 mph (89–105 km/h)  None  55–65 mph (89–105 km/h)  45–65 mph (72–105 km/h)  20–25 mph (32–40 km/h)  
American Samoa  no freeways or divided roads in American Samoa  25–30 mph (40–48 km/h)^{[2]}^{[11]}  15 mph (24 km/h)^{[11]}  
Arizona^{[12]}  65–75 mph (105–121 km/h)  55–65 mph (89–105 km/h)  None  55–65 mph (89–105 km/h)  45–65 mph (72–105 km/h)  20–25 mph (32–40 km/h)  
Arkansas^{[13]}  70–75 mph (113–121 km/h)  70 mph (113 km/h)  60–65 mph (97–105 km/h)  None  65 mph (105 km/h)  55–65 mph (89–105 km/h)  20–30 mph (32–48 km/h) 
California  65–70 mph (105–113 km/h)  55 mph (89 km/h)  50–65 mph (80–105 km/h)  None  65 mph (105 km/h)^{[14]}  55–65 mph (89–105 km/h)  25–30 mph (40–48 km/h) 
Colorado  65–75 mph (105–121 km/h)  55–75 mph (89–121 km/h)  None  55–65 mph (89–105 km/h)  55–65 mph (89–105 km/h)  20–35 mph (32–56 km/h)  
Connecticut  65 mph (105 km/h)  45–65 mph (72–105 km/h)  40 mph (64 km/h)  50–55 mph (80–89 km/h)  45–50 mph (72–80 km/h)  20–40 mph (32–64 km/h)  
Delaware^{[15]}  65 mph (105 km/h)  50–65 mph (80–105 km/h)  None  55 mph (89 km/h)  50 mph (80 km/h)  25–35 mph (40–56 km/h)  
District of Columbia^{[16]}  no rural freeways in D.C.  40–55 mph (64–89 km/h)  None  no rural roads in D.C.  25 mph (40 km/h)  
Florida^{[17]}  70 mph (113 km/h)  45–70 mph (72–113 km/h)  40–50 mph (64–80 km/h)  55–70 mph (89–113 km/h)  55–60 mph (89–97 km/h)  20–50 mph (32–80 km/h)  
Georgia^{[18]}  70 mph (113 km/h)  55–70 mph (89–113 km/h)  None  55–65 mph (89–105 km/h)  45–55 mph (72–89 km/h)  25–45 mph (40–72 km/h)  
Guam^{[19]}^{[20]}^{[21]}  no freeways in Guam  35–45 mph (56–72 km/h)  35–45 mph (56–72 km/h)  35 mph (56 km/h)  
Hawaii  55–60 mph (89–97 km/h)  45–50 mph (72–80 km/h)  35–45 mph (56–72 km/h)  45–55 mph (72–89 km/h)  45–60 mph (72–97 km/h)  25 mph (40 km/h)  
Idaho  70–80 mph (113–129 km/h)  70 mph (113 km/h)  60–65 mph (97–105 km/h)  None  65–70 mph (105–113 km/h)  55–70 mph (89–113 km/h)  25–35 mph (40–56 km/h) 
Illinois  70 mph (113 km/h)  45–70 mph (72–113 km/h)  45 mph (72 km/h)  55–65 mph (89–105 km/h)  45–55 mph (72–89 km/h)  20–30 mph (32–48 km/h)  
Indiana  70 mph (113 km/h)  65 mph (105 km/h)  50–70 mph (80–113 km/h)  None  55–60 mph (89–97 km/h)  50–55 mph (80–89 km/h)  20–30 mph (32–48 km/h) 
Iowa  65–70 mph (105–113 km/h)  55–65 mph (89–105 km/h)  40 mph (64 km/h)  65 mph (105 km/h)  45–55 mph (72–89 km/h)  25 mph (40 km/h)  
Kansas  75 mph (121 km/h)  55–75 mph (89–121 km/h)  40 mph (64 km/h)  65–70 mph (105–113 km/h)  55–65 mph (89–105 km/h)  20–30 mph (32–48 km/h)  
Kentucky^{[22]}  70 mph (113 km/h)  50–70 mph (80–113 km/h)  None  65 mph (105 km/h)  55 mph (89 km/h)  25–45 mph (40–72 km/h)  
Louisiana^{[23]}  70–75 mph (113–121 km/h)  50–70 mph (80–113 km/h)  55–65 mph (89–105 km/h)  45–55 mph (72–89 km/h)  20–45 mph (32–72 km/h)  
Maine  70–75 mph (113–121 km/h)  50–65 mph (80–105 km/h)  45–55 mph (72–89 km/h)  45–55 mph (72–89 km/h)  25 mph (40 km/h)  
Maryland^{[24]}^{[25]}  70 mph (110 km/h)  55 mph (89 km/h)  50 mph (80 km/h)  15–35 mph (24–56 km/h)  
Massachusetts  65 mph (105 km/h)  45–65 mph (72–105 km/h)  45–55 mph (72–89 km/h)  45–55 mph (72–89 km/h)  20–30 mph (32–48 km/h)  
Michigan^{[26]}  70–75 mph (113–121 km/h)^{[27]}  65 mph (105 km/h)  55–70 mph (89–113 km/h)  4555 mph (7289 km/h)  55–65 mph (89–105 km/h)  55–65 mph (89–105 km/h)^{[27]}  25 mph (40 km/h) 
Midway Atoll^{[4]}  no freeways or divided roads in the Midway Islands  15 mph (24 km/h)  
Minnesota^{[28]}^{[29]}  70 mph (113 km/h)  45–65 mph (72–105 km/h)  40 mph (64 km/h)  60–65 mph (97–105 km/h)  55–60 mph (89–97 km/h)  30 mph (48 km/h)  
Mississippi  70 mph (113 km/h)  55–70 mph (89–113 km/h)  65 mph (105 km/h)  55 mph (89 km/h)  25 mph (40 km/h)  
Missouri  70 mph (113 km/h)  45–70 mph (72–113 km/h)  60–70 mph (97–113 km/h)  45–65 mph (72–105 km/h)  25–40 mph (40–64 km/h)  
Montana  75–80 mph (121–129 km/h)  70 mph (113 km/h)  65 mph (105 km/h)  65–70 mph (105–113 km/h)  55–70 mph (89–113 km/h)  20–25 mph (32–40 km/h)  
Nebraska^{[30]}  75 mph (121 km/h)  50–75 mph (80–121 km/h)  65–70 mph (105–113 km/h)  55–65 mph (89–105 km/h)  25 mph (40 km/h)  
Nevada  70–80 mph (113–129 km/h)^{[31]}^{[32]}  65 mph (105 km/h)  65–75 mph (105–121 km/h)  55–70 mph (89–113 km/h)  20–30 mph (32–48 km/h)  
New Hampshire  65–70 mph (105–113 km/h)  45–65 mph (72–105 km/h)  55 mph (89 km/h)  35–55 mph (56–89 km/h)  20–30 mph (32–48 km/h)  
New Jersey^{[33]}^{[34]}  65 mph (105 km/h)  50–65 mph (80–105 km/h)  55 mph (89 km/h)  30–55 mph (48–89 km/h)  20–35 mph (32–56 km/h)  
New Mexico^{[35]}  75 mph (121 km/h)  55–75 mph (89–121 km/h)  55–75 mph (89–121 km/h)  55–70 mph (89–113 km/h)  20–55 mph (32–89 km/h)  
New York^{[36]}  65 mph (105 km/h)  40–65 mph (64–105 km/h)  45–55 mph (72–89 km/h)  35–55 mph (56–89 km/h)  20–45 mph (32–72 km/h)  
North Carolina^{[37]}^{[38]}  65–70 mph (105–113 km/h)  50–70 mph (80–113 km/h)  55–60 mph (89–97 km/h)^{[39]}  55 mph (89 km/h)  20–35 mph (32–56 km/h)  
North Dakota^{[40]}^{[41]}  75 mph (121 km/h)  55–75 mph (89–121 km/h)  70 mph (113 km/h)^{[42]}  55–70 mph (89–113 km/h)  20–55 mph (32–89 km/h)^{[42]}  
Northern Mariana Islands^{[43]}  no freeways in Northern Mariana Islands  45 mph (72 km/h)  25 mph (40 km/h)  
Ohio^{[44]}^{[45]}  70 mph (113 km/h)  50–70 mph (80–113 km/h)  40 mph (64 km/h)  55–70 mph (89–113 km/h)^{[46]}^{[47]}  45–55 mph (72–89 km/h)  20–35 mph (32–56 km/h)  
Oklahoma  70–80 mph (113–129 km/h)  55–65 mph (89–105 km/h)  4560 mph (7297 km/h)  65–70 mph (105–113 km/h)  55–65 mph (89–105 km/h)  25 mph (40 km/h)  
Oregon  65–70 mph (105–113 km/h)  60–65 mph (97–105 km/h)  50–60 mph (80–97 km/h)  55–70 mph (89–113 km/h)  55–70 mph (89–113 km/h)  20–25 mph (32–40 km/h)  
Pennsylvania  55–70 mph (89–113 km/h)  35–70 mph (56–113 km/h)  55 mph (89 km/h)  35–55 mph (56–89 km/h)  20–35 mph (32–56 km/h)  
Puerto Rico^{[48]}  60–65 mph (97–105 km/h)  55 mph (89 km/h)  50–55 mph (80–89 km/h)  55 mph (89 km/h)  45–55 mph (72–89 km/h)  25–35 mph (40–56 km/h)  
Rhode Island^{[49]}  65 mph (105 km/h)  45–55 mph (72–89 km/h)  55 mph (89 km/h)  50 mph (80 km/h)  20–25 mph (32–40 km/h)  
South Carolina^{[50]}  65–70 mph (105–113 km/h)  50–65 mph (80–105 km/h)  45 mph (72 km/h)  60 mph (97 km/h)  45–55 mph (72–89 km/h)  20–30 mph (32–48 km/h)  
South Dakota^{[51]}^{[52]}  75–80 mph (121–129 km/h)  60–75 mph (97–121 km/h)  40 mph (64 km/h)  65–70 mph (105–113 km/h)  55–65 mph (89–105 km/h)  20–45 mph (32–72 km/h)  
Tennessee  65–70 mph (105–113 km/h)  55–70 mph (89–113 km/h)  55–65 mph (89–105 km/h)  35–65 mph (56–105 km/h)  20–35 mph (32–56 km/h)  
Texas  75–85 mph (121–137 km/h)  55–75 mph (89–121 km/h)  70–75 mph (113–121 km/h)  60–75 mph (97–121 km/h)  25–30 mph (40–48 km/h)  
U.S. Virgin Islands^{[53]}  no freeways in the United States Virgin Islands  55 mph (89 km/h)  30–40 mph (48–64 km/h)  20–25 mph (32–40 km/h)  
Utah^{[54]}^{[55]}  75–80 mph (121–129 km/h)  65–70 mph (105–113 km/h)^{[56]}  45 mph (72 km/h) Not Posted^{[57]}  55–65 mph (89–105 km/h)^{[58]}  55–65 mph (89–105 km/h)  20–35 mph (32–56 km/h)  
Vermont  65 mph (105 km/h)  55 mph (89 km/h)  55 mph (89 km/h)  50–55 mph (80–89 km/h)  20–50 mph (32–80 km/h)  
Virginia^{[59]}  65–70 mph (105–113 km/h)  55–70 mph (89–113 km/h)  None  55–60 mph (89–97 km/h)  55 mph (89 km/h)  20–35 mph (32–56 km/h)  
Wake Island^{[3]}  no freeways or divided roads in Wake Island  40 mph (64 km/h)  
Washington  70 mph (113 km/h)^{[a]}^{[60]}  60 mph (97 km/h)  60 mph (97 km/h)  60–70 mph (97–113 km/h)  55–65 mph (89–105 km/h)  20–50 mph (32–80 km/h)  
West Virginia  70 mph (113 km/h)  55–65 mph (89–105 km/h)  None  65 mph (105 km/h)  55 mph (89 km/h)  20–55 mph (32–89 km/h)  
Wisconsin^{[61]}  70 mph (113 km/h)  50–70 mph (80–113 km/h)  65 mph (105 km/h)  55 mph (89 km/h)  20–35 mph (32–56 km/h)  
Wyoming^{[62]}  75–80 mph (121–129 km/h)  60–75 mph (97–121 km/h)  70 mph (113 km/h)  55–70 mph (89–113 km/h)  30 mph (48 km/h) 
legend:  

Freeway: Interstate Highway or other state or federally numbered road built to Interstate standards. Divided: State or federally numbered road, generally with four or more lanes, not built to Interstate standards, but with a median or other divider separating directions of travel. Undivided rural: County, State, or U.S. route, generally with two to four lanes, with no separator between directions of travel. Residential Street/residential: Residential streets, business districts, or School zones.  



State  Typical fine and whether absolute or prima facie* 
Recklessness threshold or enhanced penalty  Ticket dismissal options  Point system 

Arizona  (Not available or information needed.) Prima facie (Absolute above 85 mph (137 km/h)) 
Over 35 mph (56 km/h) in a school zone, over 20 mph (32 km/h) above the posted speed limit, or over 85 mph (137 km/h) regardless of the posted speed limit.^{[63]}  Defensive driving school (requires court approval for criminal speeding tickets).  Point system leading to fines, potential license suspension, increased insurance rates, and potential jail time (if criminal). 
California  $35 for up to 15 mph (24 km/h) over, $70 for up to 125 mph (201 km/h) $100 for over 25 mph over. All traffic fines doubled in construction zones. Prima facie (Absolute above 55 mph (89 km/h) on a 2lane road or above 65 mph (105 km/h) on a divided highway) 
Over 100 mph (160 km/h) results in a mandatory court appearance and possible 30day license suspension^{[64]}  Traffic school once every 18 months, except for offenses resulting in a mandatory court appearance.  Point system with license suspensions.^{[65]} 
North Carolina  $10–$50 plus court costs.^{[66]} Speeding fines in work zones and school zones are $250 plus court costs. Absolute 
15 mph (24 km/h) over limit at a travelled speed of greater than 55 mph (89 km/h) or over 80 mph (129 km/h)  Prayer for judgment continued (PJC) available depending on the court and subject to their discretion, but not available for charges of exceeding a speed limit by more than 25 mph (40 km/h).  Point system may lead to license suspension. Exceeding the speed limit by more than 15 mph (24 km/h) with a speed of greater than 55 mph (89 km/h) or travelling faster than 80 mph (129 km/h) results in a minimum 30day license suspension.^{[67]} 
Pennsylvania  $35^{[68]} plus court and other costs. All fines doubled in active work zones. Absolute 
Over 30 mph (48 km/h) over limit  None  Point system leads to mandatory driver education and possible license suspension. 
Texas  $1–$200^{[69]} plus court fees. Doubled in active school zones when children are present or construction zones when workers are present.^{[70]} Various additional "fees" assessed by the state essentially increase the fine by around $100 on all tickets. Prima facie^{[71]} 
None^{[72]}  Defensive driving^{[73]} (once per year) or deferred disposition^{[74]} (restrictions vary, but generally at least 4 per year), but only valid if:

Point system is annual surcharge only. No provision for license suspension if surcharges are paid.^{[75]} 
Rhode Island 
(Not available or information needed) Prima facie 
One dismissal every 3 years for speed 14 mph (23 km/h) or less over limit.^{[76]}  
Virginia 
Absolute^{[81]} 
20 mph (32 km/h) over limit or over 85 mph (137 km/h)^{[82]}  Point system^{[83]} leading to fines, suspension, and mandatory driver education.^{[84]} 
Estimated Miles of Highway and Estimated Daily VehicleMiles Traveled by Traffic Volume Group  
Graphs are unavailable due to technical issues. There is more info on Phabricator and on MediaWiki.org.

Graphs are unavailable due to technical issues. There is more info on Phabricator and on MediaWiki.org.

Based on arterial and (major) collector sample data from the 2000 Highway Performance Monitoring System^{[85]} 
One of the first speed limits in what would become the United States (at the time, still a British colony) was set in Boston in 1701 by the board of selectmen (similar to a city council):
Ordered, That no person whatsoever Shall at any time hereafter ride or drive a gallop or other extream pace within any of the Streets, lanes, or alleys in this Town on penalty of forfeiting three Shillings for every such offence, and it may be lawfull for any of the Inhabitants of this Town to make Stop of such horse or Rider untill the name of the offender be known in order to prosecution^{[86]}
Further information: National Maximum Speed Law 
In response to the 1973 oil crisis, Congress enacted the National Maximum Speed Law that created the universal 55 miles per hour (89 km/h) speed limit. States had to agree to the limit if they desired to receive federal funding for highway repair. The federal government enforced the national maximum speed limit by withholding federal funding for projects whose speed limits exceeded 55 miles per hour (89 km/h). Federal highway funding is normally allocated according to 23 U.S. Code § 106,^{[87]} the National Maximum Speed Law (also known as H.R.11372  An Act to conserve energy on the Nation's highways) modified the allocation process. As stated, in part:
...the Secretary of Transportation shall not approve any project under section 106 of title 23 of the United States Code in any State which has...a maximum speed limit on any public highway within its jurisdiction in excess of 55 miles per hour...^{[88]}
In 1984, a comprehensive study by the National Research Council found that the lower speed limits contributed to saving 3,000 to 5,000 lives in 1974 and from 2,000 to 4,000 lives each year thereafter, due to slower and more uniform speeds on American highways.^{[89]}
The law was widely disregarded by motorists, even after the national maximum was increased to 65 mph (105 km/h) on certain roads in 1987 and 1988. In 1995, the law was repealed by the National Highway System Designation Act of 1995, returning the choice of speed limit to each state.^{[90]}
Upon that repeal, there was effectively no speed limit on Montana's highways for daytime driving (the nighttime limit was set at 65 miles per hour (105 km/h)) from 1995 until 1999, when the state Supreme Court threw out the law requiring a "reasonable and prudent" speed as "unconstitutionally vague."^{[91]} The state legislature enacted a 75 miles per hour (121 km/h) daytime limit in May 1999.^{[92]} Overall, the new speed limit law in Montana was found to be satisfactory to residents of the state.^{[93]}
As of May 15, 2017, 41 states have maximum speed limits of 70 mph (113 km/h) or higher. 18 of those states have 75 miles per hour (121 km/h) speed limits or higher, while 7 states of that same portion have 80 mph (129 km/h) speed limits, with Texas even having an 85 miles per hour (137 km/h) speed limit on one of its toll roads. There are 8 states that have 65 miles per hour (105 km/h) speed limits. Hawaii has the lowest maximum speed limit, with its freeways and Saddle Road being signed at up to 60 miles per hour (97 km/h).
There is mixed evidence of the 1995 repeal's effect on fatalities. On one hand, statistical records of motor vehicle fatalities indicate that total traffic deaths in the United States have declined from 41,817 that year to 32,479 in 2011, the lowest level in 60 years, before increasing to 37,133 in 2017.^{[94]}
On the other hand, the Insurance Institute for Highway Safety (IIHS) published a study in April 2019 that controlled for general time trends, the unemployment rate, percentage of young drivers, and safety belt use rate. The study concluded the increase of speed limits not only increases the speed of vehicles but can also generate additional deaths: "A 5 mph increase in the maximum state speed limit was associated with an 8.5% increase in fatality rates on interstates/freeways and a 2.8% increase on other roads."^{[95]}
Some jurisdictions set lower speed limits that are applicable only to large commercial vehicles like heavy trucks and buses. While they are called "truck speed limits", they generally do not apply to light trucks.
A 1987 study said that crash involvement significantly increases when trucks drive much slower than passenger vehicles, suggesting that the difference in speed between passenger vehicles and slower trucks could cause crashes that otherwise may not happen.^{[96]} In a review of available research, the Transportation Research Board said "[no] conclusive evidence could be found to support or reject the use of differential speed limits for passenger cars and heavy trucks" and "a strong case cannot be made on empirical grounds in support of or in opposition to differential speed limits".^{[97]}^{: 11 }^{: 109 } Another study said that two thirds (67%) of truck/passenger car crashes are the fault of the passenger vehicle.^{[98]}
In addition to the legally defined maximum speed, minimum speed limits may be applicable. Occasionally there are default minimum speed limits for certain types of roads, generally freeways. Numeric night speed limits are occasionally used.
Traffic violations can be a lucrative income source for jurisdictions and insurance companies. For example:
Thus, an authority that sets and enforces speed limits, such as a state government, regulates and taxes insurance companies, who also gain revenue from speeding enforcement. Furthermore, such an authority often requires "all" drivers to have policies with those same companies, solidifying the association between the state and auto insurers. If a driver cannot be covered under an insurance policy because of high risk, the state will assume that high risk for a greater monetary amount; thus resulting in even more revenue generation for the state.^{[106]}
When a speed limit is deemed to be used to generate revenue, it is called a speed trap. The town of New Rome, Ohio was such a speed trap, where speeding tickets raised up to $400,000 per year to fund the police department of a 12acre village with 60 residents.^{[107]}
Reduced speed limits are sometimes enacted for air quality reasons. The most prominent example includes Texas' environmental speed limits.
Either of the following qualifies a crash as speedrelated in accordance with U.S. government rules:^{[108]}
Speeds in excess of speed limits account for most speedrelated traffic citations; generally, "driving too fast for conditions" tickets are issued only after an incident where the ticket issuer found tangible evidence of unreasonable speed, such as a crash. Driving too fast for conditions is sometimes cited when a motorist is caught exceeding the posted speed limit, but the speed falls below a state's "default" speed limit codified in law. This makes it difficult for the motorist to get out of a ticket by claiming the speed at which he or she was travelling was within the state's legal speed limit, despite the lower posted speed limit for which the motorist may or may not have been aware of.
A criticism of the "exceeding speed limits" definition of speeding is twofold:
Variable speed limits offer some potential to reduce speedrelated crashes. However, due to the high cost of implementation, they exist primarily on freeways. Furthermore, most speedrelated crashes occur on local and collector roads, which generally have far lower speed limits and prevailing speeds than freeways.^{[111]}
Most states have absolute speed limits, meaning that a speed in excess of the limit is illegal per se. However, some states have prima facie speed limits.^{[112]} This allows motorists to defend against a speeding charge if it can be proven that the speed was in fact reasonable and prudent.
Speed limits in various states, including Texas,^{[113]} Utah,^{[114]} Massachusetts, New Hampshire, Connecticut, Ohio, Oregon, and Rhode Island are prima facie. Some other states have a hybrid system: speed limits may be prima facie up to a certain speed or only on certain roads. For example, speed limits in California up to 55 mph, or 65 mph on highways, are prima facie, and those at or above those speeds are absolute.^{[115]}
A successful prima facie defense is rare. Not only does the burden of proof rest upon the accused, a successful defense may involve expenses well in excess of the cost of a ticket, such as an expert witness. Furthermore, because prima facie defenses must be presented in a court, such a defense is difficult for outoftown motorists.
Metric speed limits are no longer included in the Federal Highway Administration's Manual on Uniform Traffic Control Devices (MUTCD), which provides guidelines for speed limit signage,^{[116]} and therefore, new installations are not legal in the United States. Prior to 2009, a speed limit could be defined in kilometers per hour (km/h) as well as miles per hour (mph). The 2003 version of the MUTCD stated that "speed limits shown shall be in multiples of 10 km/h or 5 mph."^{[117]} If a speed limit sign indicated km/h, the number was circumscribed and "km/h" was written below. Prior to 2003, metric speed limits were designated using the standard speed limit sign, usually with yellow supplemental "METRIC" and "km/h" plaques above it and below it, respectively.^{[118]}
In 1995, the National Highway System Designation Act prohibited use of federal funds to finance new metric signage.