4.5 MOEs
MOEs objectively report project conditions involving specific criteria. Traffic analysis MOEs are often related to mobility and may also include safety, accessibility, reliability, or others (see Chapter 5 and Chapter 6 for Safety MOEs). Analysis tools selected for a project often determine which MOEs will be used to evaluate project conditions. However, projectspecific circumstances could merit the selection of a certain MOE, in which case analysis tool selection could be MOEdependent. Common MOEs reported by common analysis tools are provided in . MOEs can be selected when completing a quantitative analysis. The number and type of MOEs selected are dependent on the goals and objectives of the project.
MOEs Reported | Units | CAP-X | TDM | FREEVAL | HCS | Synchro | SIDRA | Vissim | CORSIM | SimTraffic |
|---|---|---|---|---|---|---|---|---|---|---|
Control Delay | Sec/veh | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ a | ✔ | ✔ |
Density | Pcpmpl | ✔ | ✔ | ✔ | ✔ | ✔ | ||||
Percent of Free-Flow Speed | % | ✔ | ✔ | ✔ | ||||||
Percent Time Spent Following | % | ✔ | ||||||||
Queue Length | veh or ft | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | |||
Reliability | ✔ | |||||||||
Travel Speed | mph | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | |
Travel Time | Sec | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | |||
Volume-to-Capacity Ratio | # | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | |||
Service Measure (LOS) | A-F | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | |
Vehicle Miles of Travel | VMT | ✔ | ✔ | |||||||
Vehicles Hours of Travel | VHT | ✔ | ✔ | |||||||
Vehicle Hours of Delay | VHD | ✔ | ✔ | |||||||
Freeways: Percent Breakdowns | % | ✔ | ✔ | ✔ | ✔ | |||||
Throughput | Veh/hr | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ |
The checkmarks represent the MOEs a certain tool can output
a
Vissim’s control delay is calculated differently than the Highway Capacity Manual4.5.1 Control Delay
Control delay is expressed as seconds per vehicle (sec/veh). Per the HCM, control delay is defined as “delay brought about by the presence of a traffic control device, including delay associated with vehicles slowing in advance of an intersection, the time spent stopped on an intersection approach, the time spent as vehicles move up in the queue, and the time needed for vehicles to accelerate to their desired speed.”
4.5.2 Density
Density is expressed as passenger cars per mile per lane (pcpmpl) or vehicles per mile per lane (vpmpl). Per the HCM, density is defined as “the number of vehicles occupying a given length of a lane or roadway at a particular instant.” Truck volume can be converted to passenger car volume by using a passenger car equivalent factor.
4.5.3 Percent of Free-Flow Speed (PFFS)
Free-flow speed is defined as “the average speed of vehicles on a given segment, measured under low-volume conditions, when drivers are free to drive at their desired speed and are not constrained by the presence of other vehicles or downstream traffic control devices.” PFF) is expressed as a percentage. Per the HCM, PFFS is defined as “the average travel speed (ATS) divided by the free-flow speed.”
4.5.4 Percent Time-Spent-Following
Percent time-spent-following (PTSF) is expressed as a percentage. Per the HCM, PTSF is defined as “the average percentage of travel time that vehicles must travel in platoons behind slower vehicles because of the inability to pass.” A platoon consists of vehicles or pedestrians that travel together as a group, either because of traffic control devices, roadway geometry, or other factors.
4.5.5 Queue Length
Queue length, often reported in terms of 95thpercentile or as a queue-to-storage ratio, is typically expressed as feet but can also be reported as the number of vehicles queued. Per the HCM, queue length is defined as “the distance between the upstream and downstream ends of the queue.” A queue length in the 95th percentile indicates the length which has a five percent probability of being exceeded during a given analysis period. Queue-to-storage ratio is a numeric value equaling the ratio of 95th-percentile queue length to the storage length of the corresponding movement. Queue-to-storage ratios greater than one indicate incomplete storage.
4.5.6 Reliability
Reliability, specifically travel time reliability, quantifies the variation of travel time. Per the HCM, reliability is defined as “the entire range of travel times for a given trip for a selected time period and over a selected horizon.” Reliability is expressed in terms of variability or in terms of success or failure with respect to a specific target. To measure reliability, a history of travel times over a selected horizon (for example, a year) is necessary to create a travel time distribution.
4.5.7 Speed
Speed, specifically SMS, is expressed as miles per hour (mph). Per the HCM, SMS is defined as “an average speed based on the average travel time of vehicles to traverse a length of roadway.”
4.5.8 Travel Time
Travel time is expressed as seconds (sec). Per the HCM, travel time is defined as “the average time spent by vehicles traversing a highway segment, including control delay.”
4.5.9 Volume to Capacity Ratio
Volume to capacity (v/c) ratio is a numeric value equaling the ratio of traffic volume to facility capacity. v/c ratios greater than one indicate capacity failure.
4.5.10 Freeways: Percent Breakdowns
Percent breakdowns is expressed as a percentage. Per FHWA’s Traffic Analysis Toolbox Volume VI, breakdown is defined as “a density of vehicles per lane greater than the density at capacity flow rate.” Percent breakdown can be computed both geographically, as a percent of directional freeway miles, and temporally, as a percent of analysis period. A higher percent breakdown indicates more congested freeway operations.
4.5.11 Throughput
Per the HCM, throughput is defined as “the number of persons or vehicles passing a point on a transportation facility during a given time period.” Per FHWA’s Traffic Analysis Toolbox Volume VI, the throughput of different alternatives is compared “to determine the relative productivity of each alternative.”
4.5.12 Level-of-Service (LOS)
LOS is expressed as letter grades A through F. Per the HCM, LOS is defined as “a quantitative stratification of a performance measure or measures representing quality of service.” Service or performance measures are specific MOEs selected for the project which will be classified into LOS grades. Typically, LOS grades of A-D represent acceptable MOE values, LOS E represents near the failure range of the MOE, and LOS F represents conditions which are failing or past the failing threshold of the specific MOE.
4.5.13 Vehicle Hours Traveled (VHT)
VHT is the total time it takes for all vehicles in a network to finish their trips. VHT includes 4-15 2024 | Traffic and Safety Analysis Procedures Manual congested travel time and is commonly used to measure overall network delay.
4.5.14 Vehicle Miles Traveled (VMT)
VMT is the amount of distance traveled by all vehicles in a geographic region over a given period. VMT is important for Planning-stage analysis because it shows travel pattern changes over time. VMT measures travel demand and is useful for determining infrastructure needs. High VMT values in a TDM may be indicative of circuitous trips in a network, which could be reduced by adding thoroughfares or by providing more connectivity.
4.5.15 Vehicle Hours of Delay (VHD)
VHD is calculated by taking the difference between travel times at free-flow speed and travel times at average speeds. This measure of effectiveness quantifies the extra time it takes vehicles to travel through the network due to congestion.