At-Grade Intersection

Types of Intersection Maneuvers Source: FHWA Roundabout Guide

32 4-way Intersection conflict points  High speed impacts  High angle impacts SAFETY This a 4-way intersection, just like all the ones you drove through coming here today. The lines are the paths cars take The dots are CONFLICT POINTS where paths cross and cars collide Most of the dots are in the middle <CLICK>. There are total of 32 conflict points <CLICK>. That’s also where the high-speed, <CLICK>. high-angle crashes occur, which are the most lethal

Motor Vehicle conflicts Roundabout 8 conflict points 75% reduction in Motor Vehicle conflicts  Low speed impacts SAFETY This is a roundabout. The circulating lane The path of entering cars <CLICK> There are only 8 CONFLICT POINTS <CLICK>. That’s 75% reduction in conflict points No other design produces such a large reduction in conflict points <CLICK>. All conflicts are LOW SPEED impacts, due to the slow speeds of Roundabout <CLICK>. All conflicts are LOW ANGLE merge impacts, due to the geometrics of Roundabout  Low angle impacts

BEFORE AFTER

Intersection Control Hierarchy No Control (Basic Rule) Yield Sign Stop Sign – normal control method All-Way Stop Roundabout Traffic Signal Grade Separation

Traffic Signals Advantages Orderly movement of traffic Reduces certain types of crashes Interrupts heavy flows for minor movements Promotes driver confidence Provides gap for minor movements When properly designed and located

Traffic Signals Disadvantages Increases total delay, especially off-peak Increases fuel consumption Increases crashes Induces road users to less appropriate routes Unnecessary delay if not properly located Bad timing, bad engineer!

GRADE SEPARATION High flows Minimal delays Expensive

At-Grade Railway Crossings Horizontal alignment Intersection at right angle on a tangent section No other nearby intersections Vertical alignment Intersection as level as possible Adequate view of crossing Vertical profile should prevent vehicles with low clearance from being caught on the track (see below)

Traffic Lane

Auxiliary Lanes

Auxiliary Lanes Auxiliary lanes: remove accelerating or decelerating vehicles from the through lanes store turning vehicles increase road capacity Types of acceleration or deceleration lanes parallel lanes directional lanes (tapers)

Auxiliary Lanes Tapers MEDIAN MEDIAN

Lane Shift

Offset Left-Turn Lanes

Offset Left-Turn Lanes

Continuous Left-Turn Lanes

Minimum Design for U-Turns Exhibit 9-92

Objectives of Channelization and Design Elements to Achieve Them

Design of Channelization q

Design of Channelization

Design of Channelization

Design of Channelization

Design of Channelization

Design of Channelization (Type 1)

Design of Channelization (Type 1)

Design of Channelization

Design of Channelization (Type 2)

Design of Channelization (Type 2)

Design of Channelization

Design of Channelization (Type 3)

Design of Channelization (Type 3)

Design of Channelization

Design of Channelization (Type 4)

Design of Channelization (Type 4)

Design of Channelization

Design of Channelization

Traffic Island

Simultaneous Left-Turn Lanes Exhibit 9-99

Corner Cut

Appendix

Sight Obstruction Hidden Vehicle

Auxiliary Lanes

Continuous Left-Turn Lanes 3.0 - 4.8 m

Offset Left-Turn Lanes

Traffic Island