ATMS22-Variable Speed Limits (Service Package*)

Description

This service package sets variable speed limits along a roadway to create more uniform speeds, to promote safer driving during adverse conditions (such as fog), and/or to reduce air pollution. Also known as speed harmonization, this service monitors traffic and environmental conditions along the roadway. Based on the measured data, the system calculates and sets suitable speed limits, usually by lane. Equipment over and along the roadway displays the speed limits and additional information such as basic safety rules and current traffic information. The system can be centrally monitored and controlled by a traffic management center or it can be autonomous.

This service establishes variable speed limits and communicates the speed limits to drivers. Speed warnings and enforcement of speeds limits, including variable speed limits, is covered in the ATMS19-Automated Speed Warning and Enforcement service package.

Variable speed limits are an Active Traffic Management (ATM) strategy and are typically used in conjunction with other ATM strategies (such as ATMS23-Dynamic Lane Management and Shoulder Use and ATMS24-Dynamic Roadway Warning).

Service Package Graphic

Traffic Equipment MaintenanceRoadway Variable Speed LimitsRoadway Equipment CoordinationTMC Variable Speed LimitsCollect Traffic SurveillanceRoadway Basic SurveillanceRoadway Traffic Information DisseminationTMC Traffic Information DisseminationTraffic ManagementOther RoadwayRoadwayRoadway EnvironmentDriverTrafficTraffic Operations Personneltraffic flowtraffic imagestraffic sensor controlvideo surveillance controlroadway equipment coordinationtraffic operator datavariable speed limit controltraffic operator inputsvariable speed limit statusroadway information system statusroadway information system dataenvironmental conditionsdriver informationtraffic characteristics

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Associated Planning Factors and Goals

Planning Factor Goal
A. Support the economic vitality of the metropolitan area, especially by enabling global competitiveness, productivity, and efficiency; Support regional economic productivity and development
B. Increase the safety of the transportation system for motorized and nonmotorized users; Improve the safety of the transportation system
G. Promote efficient system management and operation; Increase operational efficiency and reliability of the transportation system

Associated Objective Categories

Objective Category
Freeway Management: Efficiency
Freeway Management: Reliability
Freight Management: Travel Time Reliability
Safety: Vehicle Crashes and Fatalities
Special Event Management: Entry/Exit Travel Times
System Efficiency: Cost of Congestion
System Efficiency: Delay
System Efficiency: Duration of Congestion
System Efficiency: Extent of Congestion
System Efficiency: Intensity of Congestion (Travel Time Index)
System Efficiency: Travel Time
System Reliability: Non-Recurring Delay
System Reliability: Planning Time Index
System Reliability: Travel Time 90th/95th Percentile
System Reliability: Travel Time Buffer Index
System Reliability: Variability

Associated Objectives and Performance Measures

Objective Performance Measure
Annual rate of change in regional average commute travel time will not exceed regional rate of population growth through the year Y. Average commute trip travel time (minutes).
Decrease the average buffer index for (multiple routes or trips) by X percent over Y years. The buffer index represents the extra time (buffer) most travelers add to their average travel time when planning trips. This is the extra time between the average travel time and near-worst case travel time (95th percentile). The buffer index is stated as a percentage of the average travel time. Average buffer index or buffer time can be calculated using miles traveled as a weighting factor. Buffer time = 95th percentile travel time (min) – average travel time (min).
Decrease the buffer index for (specific travel routes) by X percent over the next Y years. The buffer index represents the extra time (buffer) most travelers add to their average travel time when planning trips. This is the extra time between the average travel time and near-worst case travel time (95th percentile). The buffer index is stated as a percentage of the average travel time. Average buffer index or buffer time can be calculated using miles traveled as a weighting factor. Buffer time = 95th percentile travel time (min) – average travel time (min).
Improve average travel time during peak periods by X percent by year Y. Average travel time during peak periods (minutes).
Maintain the rate of growth in facility miles experiencing recurring congestion as less than the population growth rate (or employment growth rate). Percent of lane-miles (or rail) operating at LOS F or V/C > 1.0
Reduce average time to clear event's exiting queue by X percent in Y years. Average time to clear event's exiting queue by year per event.
Reduce average travel time into and out of the event by X percent in Y years. Average travel time away from selected special events to a set of locations over a year.
Reduce average travel time into and out of the event by X percent in Y years. Average travel time to selected special events from a set of locations in the area over a year.
Reduce buffer index on regional freight routes during peak and off-peak periods by X percent in Y years. Buffer Index on regional freight routes during peak and off-peak period.
Reduce buffer index on the freeway system during peak and off-peak periods by X percent in Y years. The buffer index (represents the extra time (buffer) travelers add to their average travel time when planning trips in order to arrive on-time 95 percent of the time).
Reduce buffer time index for travelers to multiple similar special events by X percent in Y years. Buffer time index for travelers to multiple similar special events.
Reduce crashes due to road weather conditions Number of crashes and fatalities related to weather conditions
Reduce crashes due to unexpected congestion Number of crashes and fatalities related to unexpected congestion
Reduce delay associated with incidents on the freeway system by X percent by year Y. Hours of delay associated with incidents.
Reduce hours of delay per capita by X percent by year Y. Hours of delay (person-hours).
Reduce hours of delay per capita by X percent by year Y. Hours of delay per capita.
Reduce hours of delay per driver by X percent by year Y. Hours of delay (person-hours).
Reduce hours of delay per driver by X percent by year Y. Hours of delay per driver.
Reduce lane departure crashes Number of crashes and fatalities related to inappropriate lane departure, crossing or merging
Reduce non-special event VMT in the event area during events by X percent in Y years. Non-special event VMT in the event area during events over a year.
Reduce secondary crashes Number of secondary crashes
Reduce speed differential Number of crashes and fatalities related to excessive speeding
Reduce speed differential Number of speed violations
Reduce the 90th (or 95th) percentile travel times for each route selected by X percent over Y years. 95th or 90th percentile travel times for selected routes.
Reduce the annual monetary cost of congestion per capita for the next X years. Cost (in dollars) of congestion or delay per capita.
Reduce the average buffer time needed to arrive on-time for 95 percent of trips on (specified routes) by X minutes over Y years. The buffer index represents the extra time (buffer) most travelers add to their average travel time when planning trips. This is the extra time between the average travel time and near-worst case travel time (95th percentile). The buffer index is stated as a percentage of the average travel time. Average buffer index or buffer time can be calculated using miles traveled as a weighting factor. Buffer time = 95th percentile travel time (min) – average travel time (min).
Reduce the average of the 90th (or 95th) percentile travel times for (a group of specific travel routes or trips in the region) by X minutes in Y years. 95th or 90th percentile travel times for selected routes.
Reduce the average planning time for (specific routes in region) by X minutes over the next Y years. The planning time index represents the time that must be added to travel time at free-flow speeds or the posted speed limit to ensure on time arrivals for 95 percent of the trips. Planning time = 95th percentile travel time (minutes) – Travel time at free-flow speed or posted speed limit. Average planning time index or planning time can be computed using a weighted average over person miles traveled.
Reduce the average planning time index for (specific routes in region) by X (no units) over the next Y years. The planning time index represents the time that must be added to travel time at free-flow speeds or the posted speed limit to ensure on time arrivals for 95 percent of the trips. Planning time = 95th percentile travel time (minutes) – Travel time at free-flow speed or posted speed limit. Average planning time index or planning time can be computed using a weighted average over person miles traveled.
Reduce the daily hours of recurring congestion on major freeways from X to Y by year Z. Hours per day at LOS F or V/C > 1.0 (or other threshold).
Reduce the number of hours per day that the top 20 most congested roadways experience recurring congestion by X percent by year Y. Hours per day at LOS F or V/C > 1.0 (or other threshold).
Reduce the number of person hours (or vehicle hours) of delay experienced by travelers on the freeway system. Hours of delay (vehicle-hours or person-hours).
Reduce the number of person hours (or vehicle hours) of delay experienced by travelers on the freeway system. Hours of delay per capita or driver.
Reduce the percentage of facility miles (highway, arterial, rail, etc.) experiencing recurring congestion during the peak period by X percent by year Y. Percent of lane-miles (or rail) operating at LOS F or V/C > 1.0
Reduce the regional average travel time index by X percent per year. Travel time index (the average travel time during the peak period, using congested speeds, divided by the off-peak period travel time, using posted or free-flow speeds).
Reduce the share of freeway miles at Level of Service (LOS) X by Y by year Z. Miles at LOS X or V/C > 1.0 (or other threshold).
Reduce the share of major intersections operating at LOS Z by X percent by year Y. Percent of intersections operating at LOS F or V/C > 1.0
Reduce the total number of crashes in the region by X percent by year Y. Total crashes per X VMT.
Reduce the total number of fatalities and severe injuries in the region by X percent by year Y. Total fatalities per X VMT.
Reduce the total number of fatalities and severe injuries in the region by X percent by year Y. Total severe injuries per X VMT.
Reduce the variability of travel time on specified routes by X percent during peak and off-peak periods by year Y. Variance of travel time. Variance is the sum of the squared deviations from the mean. This can also be calculated as the standard deviation of travel time. Standard deviation is the square root of variance.
Reduce total person hours of delay (or travel-time delay per capita) by time period (peak, off-peak) caused by all transient events such as traffic incidents, special events, and work zones. Total person hours of delay during scheduled and/or unscheduled disruptions to travel.
Reduce total person hours of delay (or travel-time delay per capita) by time period (peak, off-peak) caused by scheduled events, work zones, or system maintenance by x hours in y years. Travel time delay during scheduled and/or unscheduled disruptions to travel.
Reduce total person hours of delay (or travel-time delay per capita) by time period (peak, off-peak) caused by unscheduled disruptions to travel. Total person hours of delay during scheduled and/or unscheduled disruptions to travel.

 
Since the mapping between objectives and service packages is not always straight-forward and often situation-dependent, these mappings should only be used as a starting point. Users should do their own analysis to identify the best service packages for their region.

Related ITS Applications of ITS Taxonomy

Classification Category ITS Application Area ITS Application(s)
Intelligent Infrastructure Arterial Management Lane Management Variable Speed Limits
Intelligent Infrastructure Arterial Management Traffic Control Variable Speed Limits
Intelligent Infrastructure Freeway Management Lane Management Variable Speed Limits
Intelligent Infrastructure Road Weather Management Traffic Control - Control Strategies Variable Speed Limits
Intelligent Infrastructure Roadway Operations & Maintenance Work Zone Management Variable Speed Limits

User Services related to this Service Package:

User Service
1.6 Traffic Control

Transaction Set Diagram





The source graphic, a Windows Metafile (WMF), for the TSD can be downloaded here: TSD

The following discusses how the National ITS Architecture provides the transportation service described by this service package. Each numbered item describes the operation of that portion of the service package identified with the corresponding number on the transaction set diagram.

  1. Equipment on the Roadway is constantly monitoring traffic conditions (traffic characteristics) including volume, speed, density, etc. which are used to determine the appropriate speed limit of each lane. The current weather and roadway conditions (environmental conditions), which can impact the speed limit, are also monitored.

  2. To obtain information about traffic, the Traffic Management Subsystem can control (traffic sensor control) and monitor (traffic flow) sensors in or along the Roadway.

  3. The Traffic Management Subsystem may obtain information on traffic (traffic images) from video equipment. The equipment can be controlled (e.g. pan/tilt/zoom) (video surveillance control) by the Traffic Management Subsystem.

  4. The Traffic Management Subsystem controls (variable speed limit control) the variable speed limit equipment on or along the roadway including that which displays the current speed limit (driver information) to Drivers. The Traffic Management Subsystem can monitor the status of this equipment (variable speed limit status).

  5. The Traffic Management Subsystem can configure, download messages and otherwise control (roadway information system data) equipment along the roadway to provide information such as basic safety rules and current traffic information to drivers. The Traffic Management Subsystem can monitor the status of this equipment (roadway information system status).

  6. The equipment on or along the Roadway used for variable speed limits can be coordinated (roadway equipment coordination) with signs, signals and Field-Vehicle Communications equipment.

  7. The entire process is under the asynchronous monitoring (traffic operator data) and control (traffic operator inputs) of Traffic Operations Personnel.