Measures of Effectiveness

Traffic Operations Measures of Effectiveness (MOEs)

UDOT requires VISSIM to be used to analyze traffic operations for freeway interchanges and innovative intersections. UDOT is currently accepting VISSIM versions 2020 up through the latest edition.  If this creates unnecessary hardship, older versions of VISSIM may be approved by UDOT Operations on a case by case basis.

The following Measures of Effectiveness (MOEs) have been formally adopted into UDOT’s Traffic Analysis Guidelines.  Note when providing MOEs in an IACR or OSA, please remember to only list MOE’s in one place to avoid accidental inconsistencies.  If its a primary interchange, the MOEs should go in the report.  If its for an intersection of less importance, it can be listed in the appendix.

Freeway Travel Times

Travel Times are to be used for freeway operations only.  Probe Traffic Data is available statewide online through Clearguide.  Travel times are not an appropriate measure for signalized movements as they are highly susceptible to the amount of time allocated to conflicting movements and the cycle lengths chosen for the signal.  The amount of time a conflicting movement is entitled to is highly dependent on the location and is therefore too arbitrary and context sensitive to be an objective measurement.

Freeway Level of Service

The link density, as measured in the VISSIM link evaluations, should be used to determine the congestion level on basic freeway segments and weaving areas. The measured density on mainline links must be less than 35 vehicles per mile to be acceptable. The table below details the LOS thresholds.

Note that the density and delay thresholds for both of these LOS tables have been informed by HCM. The HCM defines LOS thresholds using passenger cars per mile per lane (pc/mi/ln); however, freeway operations should be evaluated using VISSIM microsimulation, which explicitly models individual vehicle interactions, including heavy-vehicle effects, car-following behavior, and lane-changing dynamics. Because these effects are directly represented in the simulation, densities are to be evaluated in vehicles per mile per lane (veh/mi/ln) without converting to passenger-car equivalents.

Intersection LOS

Level of Service for individual movements and for overall intersections is to be applied using the tables below.  Intersection delay should be measured using the Vissim node evaluations. Generally LOS for individual movements is preferred over aggregating to the approach.  However, an approach-level-aggregation may be used if problematic movements represent an excessively small number of vehicles.  Delays at signalized intersections must be 55 seconds or fewer per vehicle to be considered acceptable. At unsignalized intersections, delay must be less than 35 seconds per vehicle. 

Queues at both Interchanges and Intersections

Queues at intersections should be reported for the 95th percentile queue lengths for each intersection movement using data from the VISSIM node evaluations. The 95th percentile queue lengths are useful in determining the design storage length.  This is a particularly critical value for off-ramps to ensure traffic does not back into the mainline.

% Served

The number of vehicles per movement and the % served is used to confirm that a movement is being fully served and delay values are not being artificially truncated.

Total Network Delay

The total vehicle delay should be calculated for each alternative. This total delay should include latent delay, which is the time vehicles were waiting to enter the network but were denied because of queues that have extended back into the edge of the models.