10.3.2 Stage 1 Operational Performance and ICE
CAP-X is a spreadsheet-based tool that compares anticipated v/c of various intersection types. This analysis determines the intersection type that will provide the most capacity given a set of simple traffic flow estimates. CAP-X analyzes multiple intersection types, but there are a few exceptions, such as TWSC and AWSC. An analysis in CAP-X can be completed for a large or small network. CAP-X does not account for varying costs of intersection implementation, nor an intersection’s impact on safety. The CAP-X inputs include:
- turning movement volumes (veh/hr);
- percent heavy vehicles;
- historical growth rate;
- lane assignments for each control type; and
- pre-selection of practical alternatives to be analyzed (Step 2B)
Optional CAP-X inputs include:
- Volume adjustment factor;
- Passenger car equivalent (PCE) factor;
- Critical lane volume sum limits;
- Heavy vehicle percentages; and
- Multimodal bicycle and pedestrian accessibility needs by the number of crossings for each intersection type being evaluated
10.3.2.1 Traffic Control Warrants
It is recommended that two-way stop control warrants, all-way stop control warrants, and traffic signal warrants be checked (if applicable) per the TMUTCD
(Appendix K, Section 8 – External References (Reference 7))
prior to intersection analysis. The investigation will help determine whether the intersection control type is warranted and if further analysis is necessary.10.3.2.2 TWSC Warrants
Two-way Stop-control warrants are typically checked per TMUTCD. According to the TMUTCD, the use of STOP signs on the minor-street approaches can be considered if engineering judgement indicates that a stop is always necessary because of one or more of the following conditions:
- The vehicular traffic volumes on the through street or highway exceed 6,000 vehicles per day;
- A restricted view exists that necessitates road users to stop to adequately observe conflicting traffic on the through street or highway; and/or
- Crash records indicate that three or more crashes that are susceptible to correction by the installation of a STOP sign have been reported within a 12-month period, or that five or more such crashes have been reported within a two-year period. Such crashes include right-angle collisions involving road users on the minor-street approach failing to yield the ROW to traffic on the through street or highway.
For more information regarding TWSC warrants, see Section 2B.06 in the TMUTCD.
10.3.2.3 AWSC Warrants
AWSC control warrants are typically checked per the TMUTCD. According to the TMUTCD, AWSC may be a useful safety measure at intersections if certain traffic conditions exist. Safety issues associated with AWSC include pedestrians, bicyclists, and all road users expecting other road users to stop. AWSC is used where the volume of traffic on the intersecting roads is approximately equal.
- The decision to install an AWSC is based on an engineering study.
- The following criteria is typically considered in the engineering study for an AWSC sign installation:
- Where traffic signal controls are justified, the AWSC is an interim measure that can be installed quickly to control traffic while arrangements are made for the installation of the traffic control signal.
- Five or more reported crashes in a 12-month period that are susceptible to correction by an AWSC sign installation. Such crashes include right-turn and left-turn collisions as well as right-angle collisions.
- Minimum volumes:
- The vehicular volume entering the intersection from the major street approaches (total of both approaches) averages at least 300 vehicles per hour for any eight hours of an average day; and
- The combined vehicular, pedestrian, and bicycle volume entering the intersection from the minor street approaches (total of both approaches) averages at least 200 vehicles per hour for the same eight hours, with an average delay to minor-street vehicular traffic of at least 30 seconds per vehicle during the highest hour; but
- If the 85th percentile approach speed of the major-street traffic exceeds 40 mph, the minimum vehicular volume warrants are 70 percent of the values provided in Items 1 and 2.
- Where no single criterion is satisfied, but where crash criteria and minimum volume criteria 1 and 2 are all met. Minimum volume criteria 3 is excluded from this condition.
For more information regarding AWSC warrants, refer to Section 2B.07 in the TMUTCD.
10.3.2.4 Signalized Intersection Warrants
Signal intersection warrants are checked per the TMUTCD. Typically, a signal warrant analysis comes after the determination that a signalized intersection is a viable alternative.
According to the TMUTCD, a signal warrant analysis is comprised of nine warrants, all of which are considered as part of the analysis. The warrants are:
- Warrant 1, Eight-Hour Vehicular Volume;
- Warrant 2, Four-Hour Vehicular Volume;
- Warrant 3, Peak Hour;
- Warrant 4, Pedestrian Volume;
- Warrant 5, School Crossing;
- Warrant 6, Coordinated Signal System;
- Warrant 7, Crash Experience;
- Warrant 8, Roadway Network; and
- Warrant 9, Intersection Near a Grade Crossing
For detailed information about conducting a signal warrant analysis, see
Appendix K, Section 5 - TMUTCD Signal Warrant Analysis Guidelines
. Additionally, a signal warrant analysis workbook is provided in Appendix K, Section 6 - TMUTCD Signal Warrant Analysis Spreadsheet
.