Traffic Control Systems Handbook: Chapter 5. Control and Management Concepts — Integrated Systems

Figure 5-1. Diversion Advisory Message in The INFORM (Long Island, NY) Corridor.

5.1 Introduction

Obtaining the most efficient traffic flow through a corridor involves coordination among the freeways and the surface streets in the corridor. Integrated Traffic Management Systems (ITMS) coordinate traffic control within a corridor or area. They integrate:

• Hardware with software elements
• Traffic signal systems
• Freeway management systems
• Traveler information systems (1)

Freeways in a corridor are primarily designed to serve longer trips. Where freeways are available, surface streets provide the following functions:

• Short trips
• Local land use access
• Access for freeways
• Alternates to freeways for recurrent congestion situations
• Alternates to freeways under incident conditions
• Alternates to freeway when a long queue exists on a metered ramp

Corridor control may be used to maximize throughput in a corridor consisting of a freeway and parallel surface streets. Ramp metering and motorist information devices, when appropriately used, may assist in the balancing of traffic to achieve this objective.

5.2 Traffic Management on Surface Streets

Two fundamental technologies that are used in most ITMS are closed circuit television (CCTV) cameras and changeable message signs (CMS). The following are a few ways in which CCTV and CMS can be used together to integrate freeways and surface streets in a corridor:

• Monitor traffic conditions and adjust signal timing
• Detect incidents and advise motorists
• Advise motorists of traffic problems in the area
• Monitor traffic conditions resulting from special events and advise motorists
• Assist with parking information

While signal timing is the primary means of traffic management on surface streets, a number of other techniques are described in this section for traffic management and coordinating traffic operations with freeways.

Monitoring Traffic Conditions and Adjusting Signal Timing

CCTV cameras are one of the primary methods of monitoring traffic conditions and detecting incidents. CCTV cameras allow an operator at the traffic management center (TMC) to monitor traffic on both freeways and surface streets to determine the location of congestion and incidents. If an incident or heavy congestion occurs on a freeway, traffic can be diverted to a parallel surface street, and the timing of the signals on the surface street can be modified to provide more green time in the direction parallel to the freeway.

One place where this concept is used is the INFORM system on Long Island, New York. Changeable message signs (CMS) on the freeway and at key entry ramps notify motorists of the location of incidents on the freeway. Operators at the INFORM traffic management center select appropriate signal timing plans to facilitate surface street traffic flow. Every signal has six pre-set timing plans. Three of the plans are used under normal conditions: off-peak, A.M. peak, and P.M. peak. The other three plans are used when a timing change appropriate for the incident is required. Stored incident timing plans include diversion for incidents in the eastbound and westbound directions, and in both directions. The system allows the operator to manually group signals together in the vicinity of the incident, and to select one of the incident timing plans. It is also possible to have a pre-set signal timing group, and in the case of freeway construction, all the signals in the group can be automatically set to one of the incident timing plans.

The use of CCTV on surface streets as on freeways raises the issue of privacy. CCTV cameras monitored by TMCs for traffic management purposes are not intended for the surveillance of individual vehicles or off-roadway sites. Some agencies have developed regulations to ensure that this intent is honored (2).

Detecting Incidents and Advising Motorists

One of the primary purposes of CCTV is to assist with incident detection. CCTV cameras can be located on both freeways and surface streets, and cameras are especially useful at an interchange where a camera has a view of both the freeway and the surface streets. If an incident is detected on either a freeway or surface street, CMS may be used to alert drivers and to possibly divert traffic elsewhere. CMS are discussed in greater detail in Chapter 10.

Advising Motorists of Traffic Problems in the Area

CCTV cameras can be used to find a major traffic problem, and CMS can alert drivers to the problem.

Monitoring Traffic Conditions Resulting from Special Events and Advising Motorists

CCTV cameras and CMS are useful during special events, both planned (such as a concert or a football game), as well as unplanned emergencies (such as a terrorist attack or a storm). Special events create traffic patterns that are quite different from normal. Many drivers going to a special event may not normally drive through the corridor in question, and are not familiar with alternate routes. Roadway and lane configurations may be different; for example, a normally two-way road may be converted to one-way in the peak direction, or a road may be closed for security reasons or to provide access for emergency vehicles.

Assisting with Parking Information

CCTV cameras, as well as other technologies, can monitor a large parking lot to determine which lots or sections are full, and CMS (or other methods of information dissemination) can notify drivers as to which parking lots are full or closed, and to direct drivers to parking lots that have available capacity.

5.3 Use of Transit Vehicles on Surface Streets as Probes for Traffic Incident Detection

Many transit properties have equipped or will equip transit vehicles with global positioning satellite (GPS) equipment (3). This equipment enables the geographic position of the transit vehicle to be determined. This position is then automatically communicated via bus radio to the dispatcher. When used in conjunction with computer aided dispatch (CAD) equipment, a vehicle that is later than the normally expected travel time variation from the schedule can be identified. On query from the dispatcher, the driver may confirm the presence and classification of a traffic incident. The latter step may be accomplished without voice communication through a terminal and keyboard at the driver's location.

5.4 Bus Rapid Transit Corridors

Bus rapid transit (BRT) (4) provides rapid, convenient and comfortable bus service. Components of bus rapid transit include:

• Improved running ways, including dedicated lanes and improved bus service in non-dedicated lanes.
• Enhanced and attractive stations.
• Improved vehicles.
• Frequent service.
• Simple, easily understood route structures.
• Simple lane collection and multiple door boarding, making it fast and easy to pay.
• Improved passenger information.

Running way improvements may include the following:

• Exclusive transitways.
• HOV Lanes.
• Dedicated transit lanes.
• Transit streets or malls.
• Queue jump lanes or bays.
• Signal priority for transit vehicles.

Locations in the U.S. that have deployed or are implementing BRT initiatives include:

• Los Angeles, California
• Boston, Massachusetts
• Eugene, Oregon
• Honolulu, Hawaii

1. "Symposium on Integrated Traffic Management Systems." Transportation Research Circular #404, March 1993.

2. "Policy for the Design and Operation of Closed-Circuit Television (CCTV), in Advanced Traffic Management Systems." New York State Department of Transportation, September 4, 2001.

3. "Task 3 Technical Memorandum - Transit Technology Compatibility - Route 5 Corridor Project, Capital District Transportation Authority." Dunn Engineering Associates, October 1999.

4. "BRT - Bus Rapid Transit." Transportation Research Board, 2001.

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