ICU1 and ICU2
The Intersection Capacity Utilization (ICU) Method is similar to the Circular 212 Planning method (see section Circular 212 (Planning and Operations)) with the exception that the ICU method includes signal loss time in the calculation of the overall intersection volume/capacity ratio (see J. Gould, Comparing the 1985 HCM and the ICU Methodologies, ITE Journal, August 1990), and no PCE factors are applied.
Jurisdictions using this method may use different assumed saturation flows per lane. The default saturation flows per lane for the ICU method have been set in PTV Vistro to 1600 veh/hr/lane. However, this value can be over-ridden by users.
Two ICU methods are included in PTV Vistro. One method adds the percentage loss time per cycle to the V/S ratio. The other multiplies the V/S ratio by the percentage loss time.
ICU1 is commonly used. The lost time for this method is expressed as a percentage of cycle length. The overall intersection V/C for this method is calculated as follows:
where:
- ICU1 = ICU Method No. 1
- V/S = sum of critical movement volume /saturation ratios
- Cycle = cycle length in seconds
- Loss= total intersection loss time in seconds
The ICU2 is based on material contained in an ITE Journal article in August 1990 by J. Gould. The equation is as follows:
where:
- ICU2 = ICU Method No. 2
- V/S = sum of critical movement volume /saturation ratios
- Cycle = cycle length in seconds
- Loss= total intersection loss time in seconds
The results of the two methods are similar, and the choice will depend upon which method has been accepted by local jurisdictions.
The intersection LOS is determined from the V/C ranges shown in (see section Intersection Level of Service (LOS) for ICU Methods).
Table 36: Intersection Level of Service (LOS) for ICU Methods
| Level of Service (LOS) | V/C |
|---|---|
|
LOS A |
0.000 – 0.6000 |
|
LOS B |
0.601 – 0.700 |
|
LOS C |
0.701 – 0.800 |
|
LOS D |
0.801 – 0.900 |
|
LOS E |
0.901 – 1.000 |
|
LOS F |
> 1.000 |
