ATMS

Advanced Traffic Management Systems

ATMS

• Intent of ATMS:– Improve operational control– Adapt control strategies to current/expected

traffic– Provide marginal improvements to system

capacity or throughput– Reduce congestion / delay / queues

ATMS Requires

• Control mechanism

• Surveillance function

• Communications

• Data manipulation

• Control algorithm

• Maintenance function

ATMS Requires

• Control mechanism

– Stop lights

– Barriers

– Traveler information?• How DO you control traffic on a “freeway”?

ATMS Requires

• Surveillance function – Loops– Cameras

• As data

• As images

– Other • Radar

• Vehicle probe data

ATMS Requires

• Communications

– To obtain the surveillance data, and

– Request required control system changes

ATMS Requires

• Data manipulation

– What exactly do you do with the data you have?

• Decision support systems

– Data fusion• Using data from multiple sensors

ATMS Requires

• Control algorithms – Old

• Time of day

• Fixed volumes

– New• Adaptive

• Real time volumes

• Predictive (in time or space)

ATMS Requires

• Maintenance of the system– Operational systems need a higher level

of maintenance than simple infrastructure

– Fail safe operational requirements

– How much data is enough? • 1 of 4 lanes? • What spacing of detection?)

ATMS Requires (?)

• Optional functions

– data collection

– storage, and

– performance monitoring / operations planning

Examples of TMS

• Freeway systems– Ramp metering

• Fixed time

• Local adaptive

• System level adaptive control

– Routing– Adaptive speed control

Examples of TMS

• Arterials Control Systems– Actuated & semi-actuated control– SCOOT– SCATS– OPAC– RT-TRACS– (NSATMS)– RHODES

Examples of ATMS

• Automated toll collection

• Parking systems

• Emergency response

Ramp Metering

• Objectives:– Reduce conflicts at ramp terminals– Decrease merge congestion– Reduce accident rates– Encourage diversion to/from specific ramps– Limit total volume on specific freeway

segments at specific times

Ramp Metering

• Objective: Maintain flow at maximum levels by

– Preventing flow break down– Increase total hourly throughput by maintaining

throughput– Improve speed of incident recovery– Promote/deny specific movements

Ramp Metering

• Minimize air pollution emissions and gasoline consumption by reducing stop and start movements

• Minimize ramp delays while maintaining mainline flow

• Minimize queue spillback onto arterials

Ramp Metering

Maximize freeway flow and freeway performance

is contradictory to

Minimize ramp queues and ramp delays

Ramp 1 Ramp 3 Ramp 2

A D C B

Ramp Metering

• Keys to successful operation– Know the maximum volume that can use each

ramp• Current local mainline volume• Future local mainline volume (upstream

volume)• Downstream congestion• Finding the correct balance between ramp

queue and freeway delay

Ramp Metering

• Know the Volume– Needs surveillance

• On the mainline– Approaching the merge point

– Upstream of the merge

– Downstream of the merge

• By the stop bar on the ramps

• Queue length

• Advanced queue detection

Ramp 1 Ramp 3 Ramp 2

A D C B

Ramp Metering

• Bring the data back to a central point

• This allows decisions to be made given geographic areas larger than “locally”

• Also allows data storage for later review / analysis

Ramp Metering

• Local control– minimize merge conflict

• Bottleneck algorithm – maximize ramp queue, given no current

downstream freeway delay

• Fuzzy Neural Network – trade off ramp queues against mainline flow– avoids direct use of volume

Freeway ATMS – Route Control

• Move vehicles to those routes with spare capacity

– Operational concerns• Are there parallel routes with spare capacity?

• Are there routes (ramps) where merging causes less disruption?

• Will the diversion cause more congestion than it will relieve?

Freeway ATMS – Route Control

• Route Diversion

– Political concerns - what are the impacts of route diversion?

• Are the new routes designed for that traffic?

• Are there concerns about who benefits / loses?

• Do the people/businesses that live along those routes object to their use by “pass through” traffic?

Freeway ATMS – Route Control

• Technical – How do you cause drivers to divert? What route do they take?– Traveler information (VMS / CMS / HAR /

radio)– Metering (fast versus slow)– Ramp closures– New technology (PDA messages)– Can you manage how many vehicle change

routes?• Many drivers won’t change routes

Surveillance

Surveillance

• Is necessary to manage traffic

• Without surveillance, there is no knowledge of what is occurring

Surveillance Technologies

• Loops

• Cameras

• Other technologies– Radar– Acoustic– Infrared– Other

Inductance Loop

Loops

• Advantages– Inexpensive– Easy to install– Well known attributes / mechanics– Provide

• Volume• Lane occupancy• Speed (sometimes)• Vehicle classification

Loops

• Disadvantages– Single location (non-movable)– Subject to pavement failure / degradation– Not good if channelization is likely to change– Difficult to collect vehicle classification data

• Dual loops

• Inductance signature recognition

Cameras

• Two basic technologies

– Video

– Digital image processing

Pan/Tilt/Zoom Camera

Cameras

• Conventional video– Needs a person watching

• Great for short time period

• Poor for longer time periods

– Good for incident verification– Good for public information– Not good for routine data collection

Cameras

• Digital Image Processing– Reasonably new technology (+15 years at a

reasonable price)– Several different technologies– Each with different costs / capabilities

Cameras

• Autoscope - style– A US vendor – early adopter– Uses low cost, fixed cameras– Acts like a digital loop– Has limitations in bad weather / lighting

Cameras

• Other digital image processing – Movable cameras

• Harder to calibrate

• More expensive cameras

• Multi-use cameras

– Vehicle tracking systems• Travel times

• License plate readers

Other Technologies

• Radar– Side fired / Over-head mounted– Data similar to loops– A non-intrusive sensor (easier to access)

• Acoustic– Also a non-intrusive sensor

Other Technologies

• Infrared– Both with reflector and without reflector– Non-intrusive – Not effected by weather

• Other– RF for electronic tag reading– Surface acoustic wave (SAW) for tag reading– Optical scanners (bar codes)

Other Technologies

• http://www.nmsu.edu/~traffic/

• Summary of Vehicle Detection and Surveillance Technologies Used in Intelligent Transportation Systems - Detector Handbook (under What’s New)

Surveillance

• When choosing surveillance system / technology– Type of data collected– Cost of data collection– Accuracy of data collected– Reliability of equipment– Frequency of communications– Flexibility

Type of Data

• Volume

• Vehicle presence

• Lane occupancy

• Vehicle classification

• Vehicle speed / travel time

• Weight

• ID

• Other (location? status? revenue?)

Cost of System

• Purchase

• Installation

• Operation

• Maintenance

Cost

• Purchase price– Sensor– Electronics– Communications– Software– License? (How many can you use?)

Cost

• Installation location effects cost– In ground– Below ground– Pole mounted– Bridge mounted

• Need for traffic control?• Communications• Power• Cabinets

Cost

• Operations– Power– Communications

• Bandwidth required

• Wireless / wireline

• Frequency of communications

– Staff oversight

Cost

• Maintenance– Mean time before failure (life cycle costs)– Routine maintenance requirements– External effects

• Bad weather

• Deteriorated pavement conditions

– Replacement parts (sole source?)– Ease of sensor replacement

Accuracy

• How important is it?– Can you accept small errors?

• Volume +5%

• Speed + 3 mph

• Error in reading Toll tags?

• Classification of truck

• It depends

Reliability

• What happens if a data point is missing?– Once– Frequently– Consistently but intermittently– Completely

• Fail safe design

• Graceful failure design

Reliability

• To get better reliability

– Purchase better equipment (price / warranty)– Build redundantly– Buy equipment designed for the environment it

will be placed in

• Must trade off against cost

Communications

• How often does data get transmitted from

– Sensor– Location

Communications

• Frequency of communications– Each activation?– Each second– 20 seconds– 5 minutes– 15 minutes– Hourly– Daily

Communications

• Size of data packet– Summary statistic

– Raw data

• For example– Digital image of picture

– Analog image of picture

– Count of cars made from picture

– Count of cars made from 15 minutes of pictures

Communications

• Must select communications strategy based on– Control system data need– Cost of bandwidth

• Installation

• Operation

– Redundancy / reliability