10.2 Intersection Control Evaluation (ICE) - Context

ICE, the process and analysis tools, is necessitated by the appearance of roundabouts and alternative intersection designs (RAID). The (ICE) process is used in evaluating the intersection traffic and geometric control at new or modified intersections. This chapter covers the main intersection types, evaluation process, analysis tools, and their inputs and outputs. Intersection Control Evaluation tools can be seen under
Appendix K, Sections 1, 2, and 8
.
According to FHWA, ICE (see
Appendix K, Section 8
), (ICE) is a tool that uses data and performance metrics to analyze intersection control and geometric options. ICE provides a transparent and traceable decision process to compare alternative intersection types. ICE is performed during the planning and schematic development phase and not started until after environmental documents are finalized and/or ROW acquisition is authorized. Using quantifiable measures (such as safety, capacity, cost, and impacts) to evaluate alternatives, public agencies, engineers, and planners can make more informed decisions. Quantitative measures are considered alongside qualitative measures such as multimodal needs and community vision goals to provide a balanced perspective when selecting the preferred alternative. It is recommended that the preferred alternative is context-sensitive to its surroundings and users. See FHWA’s website under
Appendix K, Section 8 – External References
 for additional technical materials, tools, and information on the ICE framework.
TxDOT’s RDM covers additional guidance for TxDOT’s approach to alternative intersection design. A link to the RDM is found in
Appendix K, Section 8 – External References (Reference 9)
.

10.2.1 ICE Workflow

The ICE process fits into project development at the earliest stages, considering all practical and feasible intersection or interchange alternatives to produce a traceable and transparent evidence-based method of proving the choice and design of an intersection/interchange. and illustrate the stages of the ICE process in the early stages of project planning.
ICE Stage 1 in the Project Workflow
Figure 10-1: ICE Stage 1 in the Project Workflow
ICE Stage 2 in the Project Workflow
Figure 10-2: ICE Stage 2 in the Project Workflow

10.2.2 ICE Applicability

ICE does not apply to development of studies or projects that involve system optimization, which is common for post-construction finetuning of operations. However, ICE is completed under the following circumstances:
  • The intersection includes a roadway designated as a State route or as part of the National Highway System.
  • The intersection or corridor improvements present opportunity to change the type of intersection or control to improve safety and/or operations.
  • The intersection will be designed or constructed using State or Federal funding.
ICE does not need to be completed (but may be considered), under the following circumstances:
  • The proposed work does not increase the vehicular footprint (as through-put) of the intersection, such as:
    • sidewalk/streetscape improvements;
    • signal permit revision;
    • minor turn lane adjustments, such as converting a short section of shoulder to a turn lane or lengthening a turn lane; and
    • resurfacing
  • Local road intersection where the proposed condition is a right-in and right-out.
  • Where routine traffic signal timing and equipment maintenance is required, such as where the build condition is being improved with signal timing optimization.
Driveway permits:
 A District has the authority to make the determination as to when ICE needs to be performed for a driveway permit.
For corridor improvement projects with multiple intersections that are likely to need a change in control to maintain operations or improve safety, ICE is applied to each intersection, but with a view to the corridor as a system. For example, it is common to use combinations of roundabouts, R-CUT and medians that restrict turning movements in or out of minor intersections or driveways. With combinations of roundabouts, the U-turn movements that are generated by an R-CUT can be accommodated more safely, especially for slow moving vehicles affected by an R-CUT
When a corridor collection of individual ICE analyses represents a system level review, documentation is recommended in the form of a summary memo that combines results and explanation of how adjacent intersection controls are interdependent, e.g., R-CUTs combined with roundabouts for U-turns.

10.2.3 Intersection Types

The analysis methods in this chapter apply to the following intersection types (see Chapter 11 for Interchanges). Unique and alternative designs are presented in the sections that follow:
Signalized:
  • Conventional Signal (Isolated, Coordinated, Clustered);
  • Signalized RCUT;
  • Quadrant Roadway;
  • Turn lane Improvements;
  • DLT; and
  • CGT
Unsignalized:
  • TWSC;
  • All-way Stop-controlled (AWSC);
  • Single Lane Roundabout;
  • Multilane Roundabout;
  • RCUT – Unsignalized;
  • RIRO w/Downstream U-Turn;
  • High-T (unsignalized Green Tee); and
  • Turn Lane Improvements
Basic descriptions of intersection types (i.e., geometric configuration, operational considerations, and safety considerations) are provided below. See provides general considerations for intersection type and the benefits each intersection type provides. Determining which type of intersection is being evaluated will help define which analysis tools to use.
Appendix K, Section 2 – Intersection Type Additional Resources
 lists additional resources used to understand various intersection types.
Appendix K, Section 7 – Intersection Type Graphics
 shows additional alternative intersections and
Appendix K, Section 8 – External References (Reference 11)
 provides a link to an alternative intersection inventory in Texas
Table 10-1: Intersection Control Selection Matrix
Intersection Type
When to Consider
Benefits
Disadvantages
Conventional Signalized (Isolated)
  • Intersections more than one mile apart
  • Built-up areas of Rural communities
  • Lower maintenance compared to coordinated
  • Isolated may have more delay than coordinated intersections
Conventional Signalized (Coordinated)
  • Intersections spaced less than a half mile apart
  • Improved operations
  • Signal progression may improve congestion
  • Signal timing plan updates to reflect changing traffic patterns are necessary.
  • 32 conflict points with moderate severity risk
Conventional Signalized (Clustered)
  • At closely spaced intersections
  • Typically, several hundred feet or less between intersections
  • Cost-efficient
  • Typically use a single signal controller for two intersections
  • Close spacing could cause vehicle stacking/storage issues.
  • 32 conflict points with moderate severity risk
Two-Way Stop-Controlled (TWSC)
  • At intersections with:
    • Moderate to heavy through traffic on a major street (>90%)
    • Low to moderate volume on a minor street (<10%)
  • Volumes that do not warrant signalization
  • Cost-efficient
  • Could cause significant delay for the side streets
  • Limited operational and safety benefits as traffic volumes become high. Left-turn and angle crossing collisions at high speeds
All-Way Stop-Controlled (AWSC)
  • At intersections with:
    • Balanced volumes on major and minor streets
  • Volumes that do not warrant signalization
  • Cost-efficient
  • Good safety performance at lowspeed intersections
  • Has the most delay of all control types
  • Unsuitable for rural highspeed intersections
  • Multilane designs are not practical
  • Limited operational and safety benefits as traffic volumes become high
Continuous Green-T (CGT)
  • At intersections with:
  • Increased vehicular safety
  • Improved operations
    • Free flow in one direction
  • Cost-efficient
  • Could initially violate driver expectancy
  • Pedestrian crossing could be more difficult
  • Decreased access within the functional area surrounding the CGT
Roundabout (See Chapter 12 for more information)
  • All intersections – both rural and urban
  • Rural high-speed intersections
  • Three or more legs
  • More than four legs
  • Increased
    • Typically, slower intersection speeds
    • Fewer conflict points
    • Fewer severe conflict points
  • Improved operations
    • Fewer delays and shorter queues
  • Long-term cost efficiency
  • No signal maintenance
  • Safest for pedestrians
  • Initial construction cost could be higher than other intersection types
  • Could disrupt progression along an arterial with traffic signals
Median U-Turn (MUT)
  • Divided roadways with wide medians
  • At intersections with:
    • Heavy through traffic
    • Moderate left-turn volumes
  • Three or four legs
  • Increased safety
  • Improved operations for through movements
  • Cost-efficient
  • Recovery of green time for through movements crossing at high volume intersections
  • Not intuitive to drivers
  • Greater ROW requirements
  • Visibility of the location for the U-turn
Restricted Crossing U-Turn (RCUT)
  • On roadways with a median
  • At intersections with heavy through or left-turn volumes on major street
  • Three or four legs
  • Where traffic signals are not warranted
  • Increased safety
  • Improved operations for the higher volume mainline
  • Cost-efficient
  • Avoids more costly and disruptive solutions, e.g. traffic signals or roundabouts
  • Not intuitive to drivers
  • Pedestrian crossing could be more difficult
  • Visibility of the location for the U-turn
  • Acceleration merge and deceleration lane change distances (LCDs) along the mainline
Displaced LeftTurn (DLT)
  • At intersections with:
    • Heavy through traffic in all directions
    • Heavy left-turn traffic
    • Limited access near intersection approaches
  • Increased
    • Reduced conflict points
  • Improved operations
    • Four phases to two phases
  • Enhanced synchronization
  • Maximizes both through traffic and high left-turn demand
  • Not intuitive for drivers
  • Pedestrian crossing could be more difficult
  • Restricted U-turn possibilities.
  • Traffic signal timing coordination with adjacent intersections
Grade-Separated Intersection
  • Constrained space for a larger intersection or interchange footprint
  • At intersections with:
    • Heavy through traffic on a major street
    • Moderate left-turn volumes
  • Increased capacity and uninterrupted flow
  • Accommodates U-turns
  • Increased safety Reduced vehicle conflicts and delay
Could be more costly than other intersection alternatives

10.2.3.1 Signalized Intersection

Compared to unsignalized intersections, signalized intersections increase capacity, reduce right-angle crashes, and permit vehicles, pedestrians, and bicyclists from minor volume approaches to safely cross an intersection. However, they create off-peak delay to minor approaches, increase frequency of rear-end crashes, increase congestion, and have high maintenance costs. TMUTCD signal warrants are recommended to be met before an intersection is converted into a signalized intersection. Signalized intersections are comprised of the following subcategories: isolated, coordinated, and clustered.

10.2.3.2 Coordinated Signalized Intersection

Coordinated intersections include two or more intersections that promote progression between each other along a corridor. According to the National Association of City Transportation Officials’ (NACTO’s) Urban Street Design Guide, coordinated intersections are typically spaced one-half mile or less apart and provide more continuous traffic flow for major street users going from one coordinated intersection to the next. Coordinated intersections can be optimized to a specific target speed to meet the lower speed needs of bicyclists and pedestrians.

10.2.3.3 Cluster Intersection

According to the HCM, groups of two or more intersections that are closely spaced and work operationally together using displaced or distributed movements are clustered intersections. It is recommended that these intersection clusters be analyzed as one system. Most alternative intersections are made of clustered intersections due to left-turn or U-turn movements that occur either before or after the main intersection.

10.2.3.4 Continuous Green-T (CGT)

In a High-Tee (Unsignalized CGT) or CGT intersection, one major street movement passes through the intersection without stopping. This movement typically occurs on the opposite side of the side street (on top of the “T”). The other major street direction of travel is typically uncontrolled or controlled by a traffic signal. Vehicles turning left from the side street to the major street use a left-turn pocket and merge with the major street through traffic. CGT intersections are not suitable for highspeed roadways (> 55mph). CGT intersections can be difficult for pedestrians to cross. See for the basic features of a CGT.
Continuous Green-T Features
Figure 10-3: Continuous Green-T Features (1)
Source: Virginia Department of Transportation, 03/05/2024

10.2.3.5 Restricted Crossing U-Turn (RCUT)

This alternative intersection can either have traffic signals or be stop controlled. RCUTs have directional medians to force minor street through and left-turning traffic to make a right-turn and then a U-turn on the major street to complete their maneuvers. When analyzing operations or safety of an RCUT intersection, the analysis typically includes the core intersection as well as the satellite intersections. See for the basic features of an RCUT intersection.
Restricted Crossing U-Turn Features
Figure 10-4: Restricted Crossing U-Turn Features
Source: Virginia Department of Transportation, 03/05/2024

10.2.3.6 Median U-Turn (MUT)

At MUT intersections, left-turning traffic on the major and minor street U-turn at wide medians to complete their maneuver. This eliminates the need for left turn phases at the intersection. When analyzing operations or safety of a MUT intersection, the analysis typically includes the core intersection as well as the travel time and delay at the satellite intersections. See for the basic features of a MUT intersection.
Median U-Turn Features
Figure 10-5: Median U-Turn Features
Source: Virginia Department of Transportation, 03/05/2024

10.2.3.7 Displaced Left-Turn (DLT)

Also known as a continuous flow interchange (CFI) or crossover displaced left-turn (XDLT), this signalized intersection type relocates one or more left-turn movements on an approach to the other side of the opposing traffic flow. Signals are placed at crossover intersections upstream of the main intersection and left-turn movements run simultaneously with the through movement, eliminating the need for a left-turn phase for that approach. When analyzing operations or safety of a DLT intersection, the analysis typically includes the core intersection as well as the satellite intersections. See for the basic features and flow patterns of a DLT. This intersection type requires restriction of access within the influence area of the layout. Right-in and right-right access may be permitted but not close to the cross-over areas
Displaced Left-Turn Features
Figure 10-6: Displaced Left-Turn Features
Source: Virginia Department of Transportation, 03/05/2024

10.2.3.8 Two-way Stop-controlled (TWSC)

TWSC intersections are comprised of one uncontrolled street and one stop-controlled street (see ). A typical configuration of TWSC intersections is a four-leg intersection with an uncontrolled major street and a stopcontrolled minor street. Another typical configuration is a three-leg intersection where the third leg (minor street) is stop-controlled, and the major street is uncontrolled. TWSC are typically applied at locations with a large majority of overall intersection traffic occurring on the major street. Safety analysis of TWSC intersections is discussed in
Section 10.3
 of this chapter or in
Chapter 5
 and
Chapter 6
.
TWSC Intersection
Figure 10-7: TWSC Intersection

10.2.3.9 All-way Stop-controlled (AWSC)

At AWSC intersections, all approaches have stop control (see ). AWSC are typically applied at locations with a balanced volume of vehicles traveling on intersecting segments. Operational analysis of AWSC intersections is dependent on traffic patterns at the intersection because delay at each approach is dependent on the arrival patterns of the other approaches. Safety analysis of Two-way Stop-controlled intersections is discussed later in this chapter and in
Chapter 5
 and
Chapter 6
.
AWSC Intersection
Figure 10-8: AWSC Intersection

10.2.3.10 Roundabouts

Roundabouts are circular intersections that use either signals or yield control and channelizing islands to circulate traffic in a counterclockwise motion around and through an intersection. The channelizing islands provide a refuge for pedestrians. The geometric features of a roundabout deflect and slow approaching vehicles. Roundabouts are designed to varying sizes from a single-lane mini-roundabout with a 90-foot inscribed circle diameter to a multi-lane roundabout with a 200-foot inscribed circle diameter. An
example
 of a roundabout is shown in . For more information about roundabouts (including example figures) and roundabout analysis, see
Chapter 12
.
Roundabout Features
Figure 10-9: Roundabout Features
Source: Adapted from Virginia Department of Transportation, 03/05/2024

10.2.3.11 Grade-Separated

Grade separation is a method of aligning a junction of two or more roadways at different heights (grades) so that they will not disrupt the traffic flow on other routes when they cross each other. Grade separation is typically introduced for the major street through movement, while major street turning movements and all minor street movements still occur at the same grade. See for the basic features of a grade-separated intersection.
Grade Separated Features
Figure 10-10: Grade Separated Features
Source: TxDOT Visual Dictionary - Grade Separation