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 ATMS

• Freeway systems – Ramp metering • Fixed time • Local adaptive • System level adaptive control – Routing – Adaptive speed control

Examples of ATMS

• 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

A Ramp 1 B Ramp 2 C Ramp 3 D

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

A Ramp 1 B Ramp 2 C Ramp 3 D

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