Intersection & Interchange Geometrics (IIG)Innovative Design Considerations for All Users

Module 8

Intersection-Interchange Evaluation Process

INTERSECTION CONTROL EVALUATION (ICE)

Process to determine the “best” intersection design/traffi c control for a given location

All alternatives are consideredAn evaluation of safety, operational, financial and

political impacts are compared

HISTORICAL “DEFAULTS”

Almost all intersection “problems” are solved by installing a traffi c signal

Traffi c Signal Warrants/JustificationSeparate process for other alternativesHistorical default is to only consider traditional

countermeaures traffi c signal all way stop

ICE PROCESS

All alternatives are considered Initial screening for feasibilityTechnical Analysis

Safety Capacity/Operations Costs – Benefit Costs Right of Way impacts

Public/Political ConsiderationsSelection of preferred alternative

“Best” alternative Documented in report Subject to available funding, other projects, project

readiness, etc

BENEFITS OF ICE

Quantification of “Best” alternativeDecision is documentedPotential for better decision making Important Criteria are analyzed

Safety (quantitative) Capacity (quantitative) Construction, ROW and Maintenance Costs

(quantitative) Political and Public acceptability (qualitative)

MINNESOTA ICE

Developed in 2007 with the desire to include roundabouts as an alternative to traffi c signals

Safety and Capacity Analysis is required using acceptable methods

Report documenting findings and recommendations must be submitted and approved by the District Traffi c Engineer

http://www.dot.state.mn.us/trafficeng/safety/ice/index.html

WISCONSIN

Facilities Development Manual 11-25-3 Intersection Control Evaluation

ICE Worksheet Documents the technical and financial analysis of

alternativesProject using Federal or State funding must

complete the worksheetTwo Phases (Scoping/Alternative SelectionDecision is documented

INDIANA

Intersection Design Guide (2013)First a “need” must be determined to evaluate

solutions toAll alternatives are considered, including “no build”Decision Trees help determine feasibility, eliminate

alternativesSafety, Capacity and Costs are all considered as well

as other factors

CALIFORNIA

Traffi c Operations Policy Directive (2013)

Updates evaluation procedures for determining eff ective traffi c control strategies for subject intersection

Assessment Phase – Identification of one or more strategies that will meet the “need” for control

Engineering Analysis – Safety, Capacity and Life-Cycle Costs

Establishment of District ICE coordinators

All users are considered

http://dot.ca.gov/hq/traffops/liaisons/ice.html

CALIFORNIA

SIX STEP METHODOLOGY

Ch 10 Alternative Intersection Assessment

FITS WITHIN EXISTING PROJECT DEVELOPMENT PROCESS

• The needs identified in prior planning studies should “inform” (not dictate) the identification, development, and evaluation of intersection control and geometry concepts.

• It is critical to understand the project context and intended outcomes prior to developing potential solutions so that options may be tailored to meet project needs within the opportunities and constraints of a given effort.

Step 1 – Establish Objectives

Having a clear understanding of the purpose and need is a fundamental step in evaluating alternatives

“Why are we building this project?”

Stakeholder outreach is critical to developing meaningful and appropriate objectives

Project goals and objectives (i.e. performance characteristics) should be specifi c, they should be measurable and directly relate to the purpose and needs

Step 2 – Multi-modal User AssessmentWhen considering intersection alternatives, integrate pedestrian, bicycle, and transit needs at an early stage of the project planning process. The unique characteristics of intersection options produce variations in the physical geometry and traffic control schemes which can introduce both benefits and challenges to pedestrians, bicyclists and transit users.

Step 3 – ROW & Context Assessment• Assess the overall corridor (or isolated intersection) context

including the built, natural, and community environment and the intended performance outcomes of the intersection form

• Document the intended context, and how operations, safety, and geometry fit the context for each alternative including intended users (pedestrians, bicyclists, passenger cars, transit vehicles, freight, emergency responders, and over size/over weight vehicles)

• Compare the ROW needs and economic impacts of practical alternatives

Step 4 – Access Management Assessment

Access management considerations:

• Driveway spacing• Adjacent signal spacing• U-Turns

STEP 5 – SKETCH LEVEL TRAFFIC ANALYSIS

OPERATIONAL ANALYSIS TOOL OVERVIEW

• Planning-level analysis, such as critical lane volume and Capacity Analysis for Planning of Junctions (CAP-X)

• Highway Capacity Manual (HCM) Analysis

• Microsimulation analysis

Step 5 – Sketch Level Traffic Analysis

CAP-X SPREADSHEET

Step 6 – Detailed Traffic Analysis of Viable Alternatives

Detailed traffic simulation analysis of the most promising alternatives

QUALITY OF SERVICE

Quality of service is defined as the perceived quality of travel by a road user. It is used in the 2010 HCM to assess multimodal level of service (MMLOS) for motorists, pedestrians, bicyclists, and transit riders.

Quality of service may also include the perceived quality of travel by designvehicle users such as truck or bus drivers.

INTERPRETING RESULTS

Hypothetical Cost-Effectiveness Graph of Four Alternatives

Cost

Perf

orm

an

ce

Measu

rei.e.

Inte

rsect

ion D

ela

y

Minimum Desirable LOS

Alt A

Alt G

Alt R

Alt B

QUESTIONS