Traffic Control Devices Flashcards
Design and placement of traffic control devices must consider what human factors?
- Timing
- Primacy (target value)
- Expectancy
- Redundancy
Minimum sign mounting height
Rural - 5’ above near edge of pavement
Parking/Ped Areas - 7’
Overhead - 17’
Secondary panels may be mounted 1’ lower than the clearances listed above
Lateral offset for sign placement
Rural - 12’ from edge of traveled way or 6’ from outside edge of shoulder, whichever is greater
Urban - 1’ from face of curb, or more if required by agency
Standard Sign Color - regulatory
Red
Standard Sign Color - warning
Yellow
Standard Sign Color - guide
Green
Standard Sign Color - services
Blue
Standard Sign Color - construction
Orange
Standard Sign Color - recreation
Brown
Standard Sign Color - school
fluorescent yellow-green
Standard Sign Color - incident
fluorescent pink
Standard Sign Color - electronic toll
Purple
What types of signs require retroreflectivity (or to be lit)?
Regulatory, warning, and guide
What are the message requirements for changeable message signs?
No more than
- 2 displays per message
- 3 lines with 20 characters per line
Readable at least twice by drivers traveling at the prevailing speed
Potential advantages of traffic signals
- provide for orderly movement of traffic
- reduce frequency of certain types of crashes
- increase capacity of minor street approach
- provide gaps
Potential disadvantages of traffic signals
- increase delay and fuel consumption during off-peak periods
- increase frequency of certain types of crashes
- result in driver frustration
- cause road users to choose less appropriate routes
MUTCD Signal Warrants
- Eight-hour vehicular volume
- Four-hour vehicular volumes
- Peak hour
- Pedestrian volume
- School crossing
- Coordinated signal system
- Crash experience
- Roadway network
- Intersection near a railroad grade crossing
Pretimed Control
Consistent cycle and interval lengths
Actuated Control
Responds to changing traffic flows by using detection
What size lenses are required by the MUTCD? What are the exceptions?
12”, except when:
- downstream signals are closely spaced
- circular indications when posted speed limit less than 30 mph
- circular indications for supplemental near-side signal
- supplemental signal solely for peds/bikes
Signal Phase
Sum of green right-of-way, yellow change, and red clearance intervals
Phase Numbering (ring diagram)
The signal may display one phase from one ring and one phase from the other ring… NOT two phases from the same ring and not phases that cross barriers
What is the purpose of phasing?
To minimize potential hazards at the intersection by separating conflicting vehicular and pedestrian movements
What is the threshold to consider dual left turns?
300 left turns/hour
What are the two rules of thumb for separating the left turn phase?
100+ left turns/hour
number of left turning vehicles x opposing volume > 50,000
Do short cycle lengths tend to increase or decrease overall intersection delay?
Decrease, as long as capacity is not exceeded
To provide equal quality of service to all movements, the green interval lengths should be…
proportional to traffic demand volumes per lane
What is the phase-change interval?
yellow change + red clearance
must be determined such that approach vehicles can either stop or clear the intersection
Pedestrian Timing Elements
- pedestrian start-off time
- pedestrian clearance time
- buffer time
Pedestrian Start-off Time
Time for pedestrians to step into the street and start crossing
Pedestrian Clearance Time
Time needed for pedestrians to complete the street crossing
Measured at least to far edge of farthest traveled lane or to median wide enough for pedestrian storage
Sum of pedestrian change interval + buffer interval
How does EVP obtain green time for emergency vehicles?
Existing signal phase is abbreviated. After a normal change interval, the green is transferred to the approach used by the emergency vehicle
How does TSP obtain green time for transit vehicles?
Modifies the timing of the normal sequence of operation to provide green sooner, rather than transferring out of normal sequence
Describe Pedestrian Hybrid Beacon (HAWK) operation.
- Dark unless activated.
- Flashing yellow, steady yellow, steady red during pedestrian crossing.
- Flashing red during pedestrian clearance interval.
Describe Emergency Vehicle Hybrid Beacon operation
- Dark unless activated.
- Flashing yellow, steady yellow, alternating flashing red until emergency vehicle clears intersection
Signal Coordination
Predictable time relationship between operations of each signal relative to the other signals in the system
Methods to achieve signal coordination
- Time-based coordination
- System masters with interconnect
- Computer-controlled system
What factors influence the desirability of coordinating signals?
- Signal spacing (less than 1/2 mi)
- Directional movement
- Signal phasing
- Arrival patterns (platoons)
- Traffic fluctuations (peakiness)
- Incompatible signal cycle (must be same length cycles)
What conditions favor signal removal?
Adequate sight distance
Lower traffic volumes
Crash frequency of at least 2/year
What is the purpose of pavement markings?
Indicate regulations
Supplement other devices
Guide road users
Warn road users
Pavement Marking color - white
Long lines between same direction
Edge line
Transverse markings
Words, symbols, arrows
Crosswalks
Chevron, diagonal, crosshatch
Pavement Marking color - yellow
Long lines between opposing direction
Left edge of divided highways or one-ways
Separation of TWLTL and reversible lanes
Pavement Marking color - red
Truck escape ramps
Wrong way movements
Transit lanes (interim)
Pavement Marking color - blue
Supplement white markings for handicap parking
Pavement Marking color - purple
Supplement lane/edge line markings for toll plaza approach lanes restricted to vehicles with electronic toll collection
Pavement Marking color - black
Not considered a marking color, but used for contrast
Pavement Marking color - green
Bicycle lanes (interim)
Minimum retroreflectivity for pavement markings
50 mcd/sq m/lx under dry conditions (35mph or greater)
100 mcd/sq m/lx under dry conditions (70 mph or greater)
Types of Railroad Crossing Control
Passive - signs and pavement markings
Active - flashing light signals, bells, gates
Approach Sight Distance (Railroad)
where the road user becomes aware of the presence of a crossing ahead
Corner Sight Distance (Railroad)
ability of approaching road user to see an approaching train
Clearing Sight Distance (Railroad)
visibility available to road user along the track when stopped ahead of the crossing
Work Zone Areas
Advance warning area
Transition area
Activity area
Termination area
What are the parts of a work zone activity area?
Work space
Traffic space
Buffer space
Duration- Long Term Stationary
More than 3 days
Duration- Intermediate Term Stationary
Overnight to 3 days
Duration- Short Term Stationary
Daytime, 1-12 hours
Duration- Short duration
Up to 1 hour
Duration- Mobile work
Moves intermittently or continuously along the roadway
Taper length equation
L=WS^2/60 for speeds of 40 mph or less
L=WS for speeds of 45 mph or more
Merging taper length
L
Shifting taper length
1/2 L
Shoulder closure taper length
1/3 L
Double lane closure length
L + 2L + L = 4L
What are the components of a Transportation Management Plan?
Temporary traffic control plan
Traffic operations plan
Public information plan
TSM&O
Transportation Systems Management and Operations
integrated program to optimize performance of existing infrastructure through implementation of specific systems/services that preserve capacity and improve reliability and safety
What is the goal of traffic incident management?
pre-planned coordinated approach to respond to incidents as quickly and safely as possible, to return the facility to normal operations
What approaches are used by SRTS?
Encouragement Approach
Education Approach
Engineering Approach
Enforcement Approach
