lecture 03 intersection control ( traffic engineering prof.usama shahdah )

TRAFFIC ENGINEERING COURSE

(PWE 8322)

Instructor: Usama Elrawy Shahdah, PhDLecture # 02

Intersection Control2

References

Roger P. Roess, Elena S. Prassas, William R. McShane-

Traffic Engineering

Chapter 16 in the 3rd edition

Chapter 18 in the 4th edition

Conflict points at Un-signalized intersections

T intersection

Crossing = 3

Merging = 3

Diverging = 3

Total = 9

4-leg intersection

3

TWO Factors affecting a driver’s ability to

avoid conflicts4

A driver must be able to see a potentially

conflicting vehicle or pedestrian in time to

implement an avoidance maneuver, (sight

distance related) and

The volume levels that exist must present

reasonable opportunities for a safe maneuver

to take place (gap availability related).

The Hierarchy of Intersection Control

Level I

Passive control – basic rules of the road apply

No control

Guide signs only

Warning signs with or without guide signs

Level II

Direct assignment of ROW to major street or rotational ROW

YIELD control (roundabouts are in this category)

Two-way STOP control

All-way STOP control

Level III

Positive alternate assignment of exclusive ROW

Traffic signals: 2-phase, multiphase

Traffic control agent/officer

5

18.1 Level I Control: Basic rules of the Road

Primary prerequisite for safety under basic rules-of-the-road: Sight distance must

be adequate for the driver before he/she is accountable for full responsibility for his

action. The first thing you want to check is whether adequate SSD is available at

the intersection. This must be satisfied before traffic volume concerns come into

consideration.

bd

add

dbd

abadab

dabd

ab

adbd

ab

a

bd

ad

b

A

AB

B

A

A

B

A

B

A

A

B

From the similarity

of triangles (1-3-

2 and 6-4-5):

“Visibility Triangle: Veh A is on minor street”

How do you

determine dA

and dB?

6

Rule 1: Both vehicles have at least one safe SSD to the collision

point (AASHTO recommended)

Step 1: Assume that Vehicle A (on minor street) is located one safe SSD from

the collision point. Usually the vehicle is considered to be on the minor road.

Step 2: Based on the assumed position, determine the

actual location of Vehicle B when it first becomes visible.

Call it dB(act)

Step 3: Rule 1 requires Vehicle B (on major street) to have one safe SSD.

Call it dB(min).

Step 4: If dBact > dBmin, then adequate SSD for basic rules-of-the-road has been

provided. Otherwise, violated and under Rule 1, not safe.

G

StSd A

AA01.0348.030

47.12

bd

dad

A

AB

G

StSd B

BB01.0348.030

47.12

min

7

Rule 2: Vehicle A must travel 18 feet past the collision

point in the same time that Vehicle B travels to a point 12

feet before the collision point

(min)1218

468.1

12

468.1

18

B

A

BAB

B

B

A

A

dS

Sdd

S

d

S

d

This dB is used in Step 3 in Rule 1.

Step 4 is the same as Rule 1.dA

dB

8

When dBact < dBmin then operation with no

control cannot be permitted.

Implement intersection control, using STOP- or YIELD-control, or traffic signals.

Lower the speed limit on the major street to a point where sight distances are adequate.

Remove or reduce sight obstructions to provide adequate sight distances.

9

Sample problem: Fig. 18.3, p.412

Step 1:

Step 2:

Step 3:

Step 4:

ftdA 5.196)348.0(30

)30()5.2)(30(47.1

2

ftbd

add

A

ABact 4.25

425.196

)5.196)(20(

ftd

ftd

RB

RB

0.2981230

40)185.196(

3.300)348.0(30

)40()5.2)(40(648.1

2min,

2

1min,

dBact << dBmin,R1 and dBmin,R2

Both rules were violated.

dA

dB

The sight triangle between Vehicle A and B

fails to meet the criteria for safe operation

under basic rules of the road.

10

a

b

18.2 Level II Control: Yield and STOP Control

11

YIELD or STOP

control?

If the critical

approach speed

(CAS) is between 10

to 15 mph, use

YIELD.

If less than 10 mph,

use STOP.

18.2.1

Two-way

stop sign

12

Stop Control: Sample

Problem: Figure 18.4

18ft = (10 ft from the edge of

curb to the stop line) +

(8 ft form the front bumper to the

driver)

dA-STOP = 18 + dcl

dBmin = 1.47*Smaj*tg

13

dcl = Distance from the curb line to the center of

the closest travel lane from the direction under

consideration (ft): cl = curb line. (because LTs

must enter the median lane.)

bd

add

A

AB

(Eq. 18-5)

dA-stop(from left) = 18.0 + 6.0 = 24.0 ft

dA-stop(from right) = 18.0 + 18.0 = 36.0 ft

The minimum sight distance requirement for

Vehicle B is determined using a time gap ( tg) of

7.5 s for typical conditions.

dB min =1.47*40*7.5 = 441 ft

Now the actual distance of Vehicle B from the

collision point when visibility is established is:

For most STOP-controlled intersections, the design

vehicle is the passenger car, and the criteria for left

turns are used, as they are the most restrictive.

Trucks or combination vehicles are considered only

when they make up a substantial proportion of the

total traffic on the approach. Values for right-turn

and through movements are used when no left-turn

movement is present. For these typical conditions,

AASHTO recommends the use of tg = 7.5 s.

YIELD

18.2.2 Yield control

14

18.2.3 Multiway-way

stop control16

18.3 Level III Control: Traffic Control Signals

18.3.1 Advantages of traffic signal control

Provide for the orderly movement of traffic

Increase the traffic-handling capacity of the intersection if

proper physical layouts and control measures are used

Reduce the frequency and severity of certain types of

crashes, esp. right-angle collisions

Provide for continuous or nearly continuous movement at a

definite speed when coordinated (by coordination)

Used to interrupt heavy traffic at intervals to permit other

traffic, vehicular or pedestrian, to cross

17

18.3.2 Disadvantages of traffic signal control

Excessive delay (when timing is improper)

Excessive disobedience of the signal

indications (when red interval is improperly

long) – may encourage red-light running

Increased use of less adequate routes as

road users attempt to avoid the traffic

control signal

Significant increases in the frequency of

collisions (especially rear-end collisions)

18

1. Traffic volumes in each approach, at

least 12 consecutive hours (24 hrs

count preferred) containing the

highest % of 24-hour traffic (include

two peak periods)

2. 15-min counts by approach and

movement classified by vehicle type

during the 2 hours in the AM and

PM peak periods (4 hours total)

3. Pedestrian counts in each crosswalk

during the same 4 hours in item 2

4. Information on nearby facilities and

centers serving the young, elderly,

or disabled

5. Posted or statutory speed limit

and/or the 85the percentile speed

6. A condition diagram (i.e. geometry)

(ch.11)

7. A collision diagram (ch.11)

8. For the two peak AM and two peak

PM hours:

a) Vehicle-hours of stopped delay

for each approach

b) Number and distribution of gaps

c) Speed limits

d) Pedestrian delays for at least two

30 minute peak pedestrian delay

periods

e) Queue lengths on STOP-

controlled approaches

18.3.3 Warrants for traffic signals: Data requirements

(See page 418 and 419.)

19

MUTCD has 9 warrants for a traffic signal. They are guides, not

specifications. Use professional judgments.

Warrant 1: Eight-hour vehicular volume

1a: minimum traffic volume;

1b: interruption of traffic;

1c: combination of warrants)

Warrant 2: Four-hour vehicular volume

Warrant 3: Peak hour

Warrant 4: Pedestrian volume

Warrant 5: School crossing

Warrant 6: Coordinated signal system

Warrant 7: Crash experience

Warrant 8: Roadway network

Warrant 9: Intersection near a highway-rail crossing

Warrants for Traffic Signals

20

Signal warrant 1A: 8-hour volume

Min. vehicle volume: Principal factor is the intersection traffic volume. Must

satisfy for each of any 8 hour of an average day (they do not need to be

consecutive 8 hours).

May reduce the values by 30% if the 85th percentile speed on the major approach is

greater than 40 mph or population is less than 10,000 (built-up area of isolated

community).

21

Signal warrant 1B

Interruption of continuous traffic: The volume requirements must be met for

each of any 8 hours of an average day.

May reduce the values by 30% if the 85th percentile speed on the major approach is

greater than 40 mph or population is less than 10,000 (built-up area of isolated

community).

22

Signal warrant 1C

Combination of warrants: Only in exceptional cases.

When none of the warrants are satisfied but when

the first two warrants of Warrant 1 are satisfied to

the extent of 80% of the stipulated volumes.

23

Signal warrant 2: 4-hour volume

Check for each of any

4 hr of an average day.

To meet the warrant ,

at least four hours

must plot above the

appropriate decision

curve.

24

Signal warrant 3: Peak-hour volume

Justified where traffic

condition during 1 hr of

the day result in undue

(too much) delay to traffic

on the minor street.

25

Or Signal warrant 3B: delay

This applies to cases in which

STOP control is already in

effect for the minor road.

Cannot jump from no-control

or YIELD to signals.

26

Warrant 4: Pedestrians (4 hours)

27

(a) Normal criteria

(b) Pop < 10,000, major road

speed exceeds 35 mph

If a signal is warranted only by

this warrant, start with a

semi-actuated signal. A full

actuated signal is possible

at an isolated intersection.

Another one nearby < 300 ft?

Then, this warrant is not met.

May be reduced as much as by

50% if majority of walkers

walk at less than 3.5 mph.

Fig. 18-7

28

Or, Warrant 4: Pedestrians (peak hour)

Fig. 18.8

Warrant 5: School Crossing29

The warrant requires the study of available gaps to see whether

they are "acceptable“ for children to cross through.

An acceptable gap would include:

the crossing time,

buffer time, and

an allowance for groups of children to start crossing the street.

The frequency of acceptable gaps should be no less than one

for each minute during which school children are crossing.

The minimum number of children crossing the major street is

20 during the highest crossing hour.

If only this warrant is met, use a pedestrian-actuated signal.

Warrant 6: Coordinated System30

This should not result in

signal spacing of less than

1,000 ft.

Signal warrant 7: Crash Experience

Less restrictive measures

must be used before this

warrant is used.

5 or more injury or property-

damage-only accidents within

a 12-month period, AND

signal control is a suitable

countermeasure. AND,

the traffic and pedestrian

volumes should not be less

than 80% of the requirements

of warrants 1A and 1B

31

Signal Warrant 8: Roadway Network

32

Warrant 8: Roadway Network.

When lights help to encourage

concentration and organization of

traffic networks.

(1) The total existing or

immediately projected volume

is at least 1000 during the

peak hour AND the 5-year

projected traffic volumes

satisfy the requirements of

one or more of the Warrants

1, 2, 3, on average weekday,

OR

(2) (2) The total existing or

projected entering volume is

at least 1000 vehicles for

each of any 5 hr of a

Saturday and/or a Sunday.

33

Signal warrant 9:

Intersection Near a

Highway-Rail Grade

Crossing

34

The minor-street volume used in entering either Figure18.9 or 18.10 may be multiplied by

up to three adjustment factors: (1) for train volume, (2) for presence of high-occupancy

buses, more than 20 passengers, and (3) for truck presence.

One lane approach

35




Two lane approach

36




A sample problem in application of signal warrants

39

Traffic Data

40

Warrant 141

There is no indication that the 70% reduction

factor applies

Condition A or Condition B must be met at

100%, or both must be met at 80%

Condition A is not met

Condition B is met no need to check C

Warrant 1 is satisfied

Warrant 242

Only one of the 12 hours of data is above the criterion.

To meet the warrant, four are required.

Warrant 2 is not met.

Warrant 343

None of the 12 hours of data is above the criterion.

The volume portion is not met.

Delay = 125 (The peak one-direction ) * 30 (sec/veh) = 3,750 veh-secs

3,750/3,600 = 1.04 veh-hrs < 4 veh-hrs, which required by the warrant.

The delay portion is not met

Warrant 444

The four-hour pedestrian warrant is met

peak-hour pedestrian warrant is not met.

Warrant 4 is met.

Four-Hour Pedestrian Warrant

Peak-Hour Pedestrian Warrant

Warrant 545

The school-crossing warrant does not apply.

This is not a school crossing.

Warrant 646

No information on signal progression is given, so

this warrant cannot be applied.

Warrant 7 (crash experience)47

Have lesser measures been tried? Yes, the minor

street is already STOP-controlled.

Have five accidents susceptible to correction by

signalization occurred in a 12-month period? Yes,

four right-angle, three left-turn, and three

pedestrian.

Are the criteria for Warrants 1A or 1B met to the

extent of 80%? Yes, Warrant IB is met at 100%.

The crash experience warrant is met.

Warrant 848

There is no information given concerning the

roadway network

This warrant is not applicable

Warrant 949

this situation is not a highway-rail grade crossing

location,

this warrant does not apply.

Summary50

A signal should be considered at this location because the

criteria for:

Warrant 1B (Interruption of Continuous Traffic),

Warrant 4 (Pedestrians), and

Warrant 7 (Crash Experience) are all met

The fact that Warrant IB is satisfied may suggest that a semi-actuated

signal be considered.

Warrant 4 requires the use of pedestrian signals at least for pedestrians

crossing the major street.

If a semi-actuated signal is installed, it must have a pedestrian pushbutton

(for pedestrians crossing the major street).

The number of left-turning accidents may also suggest consideration of

protected left-turn phasing

Home Reading51

Roger P. Roess, Elena S. Prassas, William R. McShane-

Traffic Engineering book

Chapter 16 in the 3rd edition

Chapter 18 in the 4th edition

52

Thanks for your time

Where do these

values come from?

My guess is…

Use the random

arrival case and use

the Poisson

distribution.

53