It starts with analysis. Synchro Pro. Then a common sense approach to building an intersection design that follows analysis. First learn the traffic patterns, and then maximize flow rates and capacity by designing smart. Not smart growth, but smart design based on common sense and putting resources like lanes and signal timing where it is most needed, eliminating waste in design. True problem solving.
3. 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
4. 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
5. 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 aYield 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 LeftTurn or RightTurn Only Signs 有禁左或者只允许
右转标志
6. Has aTraffic Officer Control 需要有现场指挥人员
7. Has a Roundabout Control 有环岛控制
6. Advantage of Traffic Signal
交通信号的好处
Orderly flow of traffic
交通有序通行
Safety forVehicles 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
7. Disadvantage of Traffic Signal
交通信号的缺点 Why NOT to install…
Major StreetTraffic Delay Increases
干道交通延误增加
Interrupt Major StreetTraffic 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
8. MUTCD Traffic Signal Warrants
MUTCD 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 UniformTraffic Devices (MUTCD).
This is because of reasons in previous slide*
ATraffic Signal should improve safety
The Most Common Warrants include:
Peak HourVolume
Easiest to compute using only a peak hour traffic count
Four HourVehicularVolume
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
*seeWhy not to install, “Disadvantage ofTraffic Signal” slide
10. 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
11. 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.
12. 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.
13. 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
14. Left Turn Lane (LOWER SPEEDS)
左转车道(较慢的速度)
ApproachTaper, BayTaper, Deceleration
Lane, and Storage Lane. Basics.
15. 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.
19. 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.
20. Freeway Interchange Details
Two lane bridge. Was stop sign control for side street frontage roads. Now is signal.
Harney Lane
SR99
27. Create the Synchro Model
Code basic roads into Synchro street system
1. Enter basic minimum intersection lanes at each
intersection.
2. Match the CAD file dimensions.
3. Enter the traffic volumes from ASSIGNMENT
4. Check Level of Service at each intersection
5. Where LOS E or worse conditions occur:
1. Propose a mitigation:
1. Add more lanes to heavy traffic movements, etc.
2. Signalize, etc.
28. Phase 1 LOS Results and
Mitigations added in First Year
29. 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.
30. Phase 2 LOS Results and
Additional Mitigations added in Year 3
31. 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
32. Phase 3 LOS Results and
Additional Mitigations added in Year 5
33. Phase 3 Mitigation DETAILS
1. Some lane
capacity added
to Intersection 2
2. Some lane
capacity added
to Intersection 3
34. Phase 4 LOS Results and
Additional Mitigations added in Year 7
35. Phase 4 Mitigations
In this fourth
set of
mitigations,
capacity is
added at
three
intersections,
and more stop
control at
another.
36. Summary of 7 year Mitigation Flow
Phase 1 Phase 2 Phase 3 Phase 4
37. Harney Phase 2 Improvements
New Pavement
added to create
new lanes and add
capacity to new
intersection
38. Harney Phase 3 Improvements
New Pavement
added to create
new lanes and add
capacity to
intersection
39. Harney Phase 4 Improvements
New Pavement
added to create
new lanes and add
capacity to
intersection
40. Harney Phase 4 Improvements
New Pavement
added to create
new lanes and add
capacity to new
intersection
42. 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
43. 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
44. Cross Section Design
Turn Lanes at least 3.0 meters wide
Same width asTHRU 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
Editor's Notes
Origin Destination Surveys
OD调查 diào chá investigation; inquiry; to investigate; to survey; survey; (opinion) poll; CL:項|项[xiang4],個|个[ge4] HSK4
The project was divided into three different components so that the various land use categories could have traffic assigned logically to differing areas of the city. Residential primarily to north and south, commercial primarily to the north, and office primarily to the south.