Intersection Conceptual Design 1Traffic Control and Geometry

TDA

Intersections.How to control?

Usually, Traffic Engineer’s task starts with a CAD design file showing only proposed curb lines通常情况下，交通工程师的任务开始时只显示建议的路边线的CAD 设计文件

宝山路

学堂路

The final task checks the CAD plan最后的任务是检查 CAD 设计方案 , and propose lane striping and control 并提出车道条纹和交通控制

宝山路

学堂路

WHY are Traffic Signals Needed? 为什么需要交通信号？

They are needed if the following less expensive options don’t solve the traffic impact need.

Without a traffic signal, an intersection is 没有交通信号，一个路口是 :

1. Uncontrolled 不受控制的2. Has a Yield Sign Control on side street 支路有让行标志3. Has a Stop Sign Control on side street 支路有停车让行标

志4. Has a Four-Way Stop Sign Control 四个方向停车让行标志5. Has No Left Turn or Right Turn Only Signs 有禁左或者只

允许右转标志6. Has a Traffic Officer Control 需要有现场指挥人员7. Has a Roundabout Control 有环岛控制

Advantage of Traffic Signal 交通信号的好处 Orderly flow of traffic

交通有序通行 Safety for Vehicles and Peds to Cross Road

车辆和行人过街安全 Cheaper than a traffic police officer

比交通警察更便宜 节省力成本 Reduces accidents (such as broadside accident)

降低了事故（如擦挂事故） Traffic Speed Control

交通速度控制

Disadvantage of Traffic Signal 交通信号的缺点 Why NOT to install… Major Street Traffic Delay Increases

干道交通延误增加 Interrupt Major Street Traffic Flow

中断干道交通流 Can Reduce Capacity of Major Street

导致干道的通行能力减少 Rear End Accidents Usually Increase

追尾事故通常会增加 False Sense of Security During Green Light

绿灯时间的盲目安全感

MUTCD Traffic Signal WarrantsMUTCD 信号灯设置标准

USDOT says that a traffic signal should not be installed unless it meets one or more warrants, as defined in Chapter 4c of the Manual on Uniform Traffic Devices (MUTCD). This is because of reasons in previous slide*

A Traffic Signal should improve safety The Most Common Warrants include:

Peak Hour Volume Easiest to compute using only a peak hour traffic count

Four Hour Vehicular Volume Can have lower volumes to qualify a traffic signal, but must be

volumes that sustain for several hours of time, hence, 4 hour counts. 信号灯设置标准

*see Why not to install, “Disadvantage of Traffic Signal” slide

Traffic Signal Warrants List 信号灯设置标准表

Warrant 1, Eight-Hour Vehicular Volume 设置标准 1, 八个小时汽车流量

Warrant 2, Four-Hour Vehicular Volume 设置标准 2, 四小时汽车流量

Warrant 3, Peak Hour 设置标准 3, 繁忙时间 Warrant 4, Pedestrian Volume 设置标准 4, 行人流量 Warrant 5, School Crossing 设置标准 5, 学校交通安全 Warrant 6, Coordinated Signal System 设置标准 6, 协调信号系统 Warrant 7, Crash Experience 设置标准 7, 交通事故的历史 Warrant 8, Road Network 设置标准 8, 路网 Warrant 9, Intersection Near Grade Crossing 设置标准 9, 路口附

近立交

Most Common: Peak Hour Warrant最常见的：高峰小时信号灯设置标准

Example:If a minor street has 200 vph approach and major street two-way total is 900 vph, a signal is NOT warranted… 300 and 1000 IS warranted… for BOTH 1 and 2 lane approaches…

if

Design Considerations for the Intersection 交叉口的设计考虑 What is the surrounding environment? 什么是周围的环境呢？

Does the needed mitigation FIT the location?是交通解决方案与环境兼容？

Is it better to consider changing: 它更好地考虑改变？1. The land use? 土地使用2. The specific project concept? 项目的概念3. The access road locations? 通路位置

Is the resulting street system developed in Synchro compatible with CAD plans and expectations? Careful! Its easy to recommend the biggest mitigation (i.e. a

tunnel or a bridge), but this may change the whole surrounding environment to something that is not visually desirable. It also may kill a project. Seek economical. Seek LOS D.

Challenge: recommending improvements with minimum environmental impacts, and have them also be pedestrian friendly.

Categorizing the Intersection 路口和道路类别

Categorize street system as: Two-lane and Multi-lane 双车道和多车道 Divided and Undivided Urban and Rural What is ULTIMATE PLAN?

For example, a “two-lane divided urban road” Standard lane width is 12 ft, and standard

shoulder width is 8 ft. In urban areas, this shoulder is often used for parking.

Choosing the Left Turn Lane It is desirable to have a left turn lane at

intersections.左转车道是可取的在路叉口

Left Turn Lane (LOWER SPEEDS)左转车道 ( 较慢的速度 ) Approach Taper, Bay Taper,

Deceleration Lane, and Storage Lane. Basics.

Considerations for Geometry几何考虑 Should be Based on traffic volumes, road capacity

应根据交通量，路容量 Symmetry is usually needed

对称性，通常需要 Must meet Industry Design criteria

必须符合工业设计标准 Design criteria considers safety and efficiency

设计标准包括安全和效率 Ignoring criteria leads to traffic problems later:

Congestion and excessive merging交通堵塞和

Accidents and confusion Empty lanes not needed, even in future Wasted or misallocated tax money

Use SYNCHRO PRO to check geometry Determine best fit based on all parameters.

Poor Alignment Lane Design

…leads to traffic operation problems with merging, etc

EXAMPLE Problem in California

PROJECTSITE

50,536 DAILY CARS 4,267 PM PEAK CARS

Known CONSTRAINTS / QUESTIONS

1. Project is Large (over 4000 cars/hour)2. Local Freeway Interchange is small

Not scheduled to improve until many years later.

3. Can Project be built without negatively impacting freeway traffic?

Caltrans (government agency for state owned roads) needs to be convinced this is OK.

4. City wants project, for taxes.5. Caltrans (State Govt) is not sure if this is

OK. Study proves whether it can work.

Freeway Interchange Details

Two lane bridge. Was stop sign control for side street frontage roads. Now is signal.

Harney Lane

SR

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Harney Lane

Interchange Limits: The BRIDGE

4267汽车 /小时

BRIDGE is only 1 lane each direction

Stages of Development

Ultimate Curb Line, 2-3 lanes in each direction, plus turn lanes

Original Street, 1 lane in each direction, Year 2006

N

Parking Lot and Road Details

NOriginal Street, 1 lane in each direction

PM Peak New Car Trips: 4267

N

1695汽车 /小时

1905汽车 /小时

320汽车 /小时

348汽车 /小时

Ultimate Intersection Geometry

N

How do we get here??

Assign Traffic.Trip Distribution ComponentPercentages

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Resid

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Create the Synchro Model

Code basic roads into Synchro street system1. Enter basic minimum intersection lanes

at each intersection.2. Match the CAD file dimensions.3. Enter the traffic volumes from

ASSIGNMENT4. Check Level of Service at each

intersection5. Where LOS E or worse conditions occur:

1. Propose a mitigation:1. Add more lanes to heavy traffic

movements, etc.2. Signalize, etc.

Phase 1 LOS Results and Mitigations added in First Year

Phase 1 Mitigation DETAILS

1. In this first set of mitigations, a signal and lane capacity is added at Intersection 2

2. 3-way Stop sign control added at Intersection 4 with some lane capacity added.

Phase 2 LOS Results and Additional Mitigations added in Year 3

Phase 2 Mitigation DETAILS

1. A signal installed at Intersection 4

2. Signal installed at Intersection 5 with some lane capacity added

3. Stop Signs added at Intersection 7

Phase 3 LOS Results and Additional Mitigations added in Year 5

Phase 3 Mitigation DETAILS

1. Some lane capacity added to Intersection 2

2. Some lane capacity added to Intersection 3

Phase 4 LOS Results and Additional Mitigations added in Year 7

Phase 4 Mitigations

In this fourth set of mitigations, capacity is added at three intersections, and more stop control at another.

Summary of 7 year Mitigation Flow

Phase 1 Phase 2 Phase 3 Phase 4

Harney Phase 2 Improvements

New Pavement added to create new lanes and add capacity to new intersection

Harney Phase 3 Improvements

New Pavement added to create new lanes and add capacity to intersection

Harney Phase 4 Improvements

New Pavement added to create new lanes and add capacity to intersection

Harney Phase 4 Improvements

New Pavement added to create new lanes and add capacity to new intersection

Harney Lane after improvements

Channelizing Design Principles

Wrong-way movements prevented by appropriate channelization Islands, medians, striping, proper alignment

Clearly define vehicle paths Striping, curbs, edge lines

Encourage SAFE speeds by design Separate points of conflict Traffic cross at right angles. Merge flat

angles Facilitate high priority movements

Alignment Design Principles

Goal: Roads meet at 90-degree angles Maximizes sight distance Minimize exposure times (accident potential)

60-degree angle intersections are: Less safe. Operational challenged.

Approach grades should be flat as practical Less than 3% grade for approach No more than 6% grade under any

circumstance

Cross Section Design

Turn Lanes at least 3.0 meters wide Same width as THRU lanes, if possible.

Curb Radius depends on “design vehicle” Use of turn templates

Traffic Island Area between lanes. Controls movements. Separate conflicts Protect pedestrians Provide definition to drivers for channels