User:Hoskir/Revision Request 4275
905.2.13 Speed Limit Guidelines
| Traffic Pamphlet |
| Speed Limits |
The following guidelines promote consistency of speed limit postings on the state of Missouri’s highway system. In all cases, engineering judgment is necessary to determine the most appropriate speed limit at a location.
905.2.13.1 Maximum Speed Limits
Maximum speed limits in Missouri are governed by the RSMo Section 304.010. The following table summarizes maximum speed limits as established by the statutes:
| Rural Areas | |
|---|---|
| 75 mph | Interstate and Freeways |
| 65 mph | Expressways |
| 55 mph | State Lettered Routes1 |
| 60 mph | All other roadways, not urbanized |
| Urbanized Areas | |
| 60 mph | Interstate, Freeways and Expressways |
| 55 mph | State Lettered Routes1 |
| 1 May be up to 60 mph based on engineering judgement | |
- The MHTC has the authority to set speed limit higher or lower than the uniform maximum speed limit established by the Missouri legislature, if recommended by the Missouri Department of Transportation.
- A review shall be conducted, in consultation with the Highway Safety and Traffic Division, prior making a change in the posted speed limits.
- At no time shall any Missouri road be posted above 75 mph.
- In 2026, RSMo Section 304.010, was modified to increase the uniform maximum speed limit on rural interstates and freeways to 75 mph.
905.2.13.1.1 Definitions (per RSMo 304.010)
Freeway: A limited access divided highway of at least ten miles in length with four or more lanes which is not part of the federal interstate system of highways which does not have any crossovers or accesses from streets, roads or other highways at the same grade level as such divided highway within such ten miles of divided highway.
Expressway: A divided highway of at least ten miles in length with four or more lanes which is not part of the federal interstate system of highways which has crossovers or accesses from streets, roads or other highways at the same grade level as such divided highway. Rural Interstate: That part of the federal interstate highway system that is not located in an urban area.
Urbanized Area: An area of fifty thousand population at a density at or greater than one thousand persons per square mile.[
905.2.13.1.2 Discrepancies
Before raising a posted speed limit above the maximums in the state statute, the district should notify the State Traffic Engineer.
Districts should coordinate across district borders to ensure consistent posted speed limits on inter-district routes in accordance with the speed limit guidelines.
905.2.13.1.3 Length of Section
Any speed limit section should have a logical beginning and ending point. Examples include city limits, roadway type changes, etc. Additionally, speed limits in unincorporated or “non-community” areas should stay consistent for a minimum of 2 miles.
905.2.13.2 Prevailing Speed Determination
Prevailing speed determination is the starting point to setting speed limits in incorporated and unincorporated areas, pursuant to the aforementioned state statutes. The prevailing speed of free-flowing traffic shall be determined using one or more of the three criteria below:
- 85th percentile speed;
- Upper limit of the 10 mph pace;
- Average test run speed.
The selected speed limit (in 5 mph increments) should not exceed the established prevailing speed by more than 3 mph.
The following factors may allow for reduction of the prevailing speed. The prevailing speed shall not be reduced below the 50th percentile (average) speed using these factors.
- Fatality and Disabling Injury Crash Rate
- Total Crash Rate
- Pedestrian Traffic
- Parking
- Adjacent Development
- Physical Roadway Conditions
905.2.13.2.1 Fatality and Disabling Injury Crash Rate
If either the fatal or disabling injury crash rates, based on reportable crashes within the proposed area, are 50% higher than the statewide average crash rate for the same roadway type, prevailing speed may be reduced by 5%.
If the fatal or disabling crash rate is more than twice the statewide rate for the roadway type, the prevailing speed may be reduced by 10%.
| Reduction Condition | Prevailing Speed Reduction |
|---|---|
| Fatal or Disabling Injury Crash Rate > 1.5 SWAR | 5% |
| Fatal or Disabling Injury Crash Rate > 2.0 SWAR | 10% |
905.2.13.2.2 Total Crash Rate
If the overall crash rate, based on reportable crashes within the proposed area, is 50% higher than the statewide average crash rate for the same roadway type, prevailing speed may be reduced by 5%.
If the crash rate is more than twice the statewide rate for the roadway type, the prevailing speed may be reduced by 10%.
| Reduction Condition | Prevailing Speed Reduction |
|---|---|
| Total Crash Rate > 1.5 SWAR | 5% |
| Total Crash Rate > 2.0 SWAR | 10% |
905.2.13.2.3 Pedestrian Traffic
Where sidewalks are not provided adjacent to the route and a total pedestrian traffic along the route exceeds 10 per hour for 3 hours of any 8-hour period, the prevailing speed may be reduced by 5 percent. Pedestrians crossing the route may only be counted if the point of crossing is not protected by a traffic control device.
905.2.13.2.4 Parking
Where parking is permitted adjacent to the traffic lane, the prevailing speed may be reduced by 5 percent.
905.2.13.2.5 Adjacent Development
Where significant adjacent development includes residential and commercial access points, the prevailing speed may be reduced to account for driveway conflicts. If necessary, this effect on the prevailing speed may be determined as outlined below.
The effect of driveway entrances can be determined by using a Driveway Conflict Number. For this purpose, a private or field entrance should have a Driveway Conflict Number of 1. Minor commercial entrances should have a number of 5. Major commercial entrances, shopping centers or industrial plant entrances that generate relatively high volumes of traffic, and public streets should have a number of 10. If the total Driveway Conflict Number exceeds a rate of 40 per mile through the proposed zone, the prevailing speed may be reduced by 5 percent. If the total number exceeds a rate of 60 per mile, the prevailing speed may be reduced by 10 percent. However, before a reduction is made due to the Driveway Conflict Number, the Poisson Curve should be used to determine if the crash reduction is statistically significant.
The test is as follows:
- a) Consult Fig. 905.2.13.2.5, using the current number of crashes for the last year.
- b) Determine the graph’s percent value from the Poisson Curve.
- c) Compute crash rate for last year.
- d) Obtain Statewide Crash Rate (SWCR). The crash data is obtained from the Transportation Management System (TMS).
- e) Calculate percent reduction between crash rate and statewide crash rate by:
- f) Compare % reduction with value obtained in step b.
- g) If % reduction equals or exceeds value obtained in step b, the Driveway Conflict Number may be used as the action would be statistically significant.
- Example:
- 8.0-mile section of roadway, AADT = 3,100, 30 crashes within last year.
- a & b). Value obtained from Fig. 905.2.13.2 = 30 %
- c).
- d). SWCR = 242.04
- e).
- f). Compare % reduction with value.
- 26.9 < 30
- Since 26.9 is less than 30, the Driveway Conflict Number cannot be considered.
905.2.13.2.6 Procedures for Obtaining Prevailing Speed Data
Spot speed studies can be made with any speed measurement device such as radar, count cards and inductive loops that determine the 85th percentile speed and the upper limit of the 10 mph pace. The 85th percentile speed is defined as the speed at or below which 85 percent of the vehicles are traveling. The 10 mph pace is defined as the 10 mph range containing the most vehicles.
Spot speed studies should be made as close to the center of the proposed zone as is practical. If the zone is lengthier than one mile, studies should be made at a minimum of two locations. If the difference in data between the two locations is minor, the higher value should be used. If the difference in data is over 5 mph, consideration should be given to designating separate zones.
Exercise care to collect the data in a manner and at times that indicate normal conditions. Normal conditions will be assumed to prevail under good weather conditions on dry pavement, following morning rush hours and prior to the evening rush hours, on any day of the week except Saturdays, Sundays or holidays. Observations should not be made immediately following a significant event or during a period of greater than normal police enforcement. Every effort should be made to disguise or conceal the fact that speeds are being reported.
Speeds should be observed for at least 100 passenger cars and pick-up trucks. Trucks over 4 tons will not be included in the data for determining a revised limit.
Average test run speeds shall be determined on the basis of at least two runs in each direction over the length of the proposed zone. The prime consideration in these test runs is to determine a maximum permissible speed. Speeds are to be recorded at 0.1 mile intervals. While making the test run, the driver will try to “float” in the traffic stream, passing as many vehicles as pass the test car.
905.2.13.3 Additional Guidelines for Establishing Speed Limits
Normally, isolated curves and turns, areas of restricted sight distance, no passing zones, etc. will not be considered as areas for lowering speed limits. The crash record on such highways will be the principal criterion.
Except on divided highways, different speeds for traffic in opposite directions cannot be used.
Speed limits shall begin at a point on or as near in advance of the point as possible where the speed limit is warranted and shall end at the point or as near the point as possible where the speed limit is not warranted.
905.2.14 Voiding City Ordinances on State Routes with Inappropriate Speed Limits
RSMo Section 304.010 contains the state laws pertaining to speed limits on Missouri’s roadways. Paragraphs 3 and 4 address speed limits on state routes and state:
- 3. On any state road or highway where the speed limit is not set pursuant to a local ordinance, the highways and transportation commission may set a speed limit higher or lower than the uniform maximum speed limit provided in subsection 2 of this section, if a higher or lower speed limit is recommended by the department of transportation. The department of public safety, where it believes for safety reasons, or to expedite the flow of traffic a higher or lower speed limit is warranted, may request the department of transportation to raise or lower such speed limit, except that no speed limit shall be set higher than seventy-five miles per hour.
- 4. Notwithstanding the provisions of section 304.120 or any other provision of law to the contrary, cities, towns and villages may regulate the speed of vehicles on state roads and highways within such cities', towns' or villages' corporate limits by ordinance with the approval of the state highways and transportation commission. Any reduction of speed in cities, towns or villages shall be designed to expedite the flow of traffic on such state roads and highways to the extent consistent with public safety. The commission may declare any ordinance void if it finds that such ordinance is:
- (1) Not primarily designed to expedite traffic flow; and
- (2) Primarily designed to produce revenue for the city, town or village which enacted such ordinance.
- If an ordinance is declared void, the city, town or village shall have any future proposed ordinance approved by the highways and transportation commission before such ordinance may take effect.
If a District Engineer believes that a city, village or town has passed an ordinance establishing an inappropriate speed limit, the District Engineer shall ensure the following actions are taken:
- Advise the city that a study will be made to determine the appropriate speed limit in the area.
- If a speed limit ordinance is found to be inappropriate as determined by a traffic engineering study and is determined to be for the purpose of producing revenue, a letter shall be sent to the city advising that their speed limit appears inappropriate and request a meeting with the city to discuss the matter.
- If a consensus cannot be obtained between the department and the city, the city would be notified of the date that the department’s recommendation will be presented to the Missouri Highways and Transportation Commission.
- If the Commission determines that the city speed limit is not correct as presently posted, the city shall be asked to adjust to the proper speed limit as determined by the Commission. If the city does not comply, the city speed limit ordinance will be declared void and posted as determined by the Commission.
- The city will then be notified of the Commission action and advised that all enforcement must be adjudicated through state courts unless the city passes and ordinance specifying the speed limit is the same as has been posted.