Lesson

Design traffic video transmission systems around the constraints of bandwidth limitations and provide provisions for remote configuration of video compression hardware.

Statewide systems implementation experience from iFlorida Model Deployment


01/30/2009
Florida,United States


Background (Show)

Lesson Learned

Florida’s Statewide Microwave System (SMS) was originally deployed in the 1980s to support emergency call boxes available at regular intervals on Florida Interstate Highways. Subsequently over the years, the combination of Road Rangers (motorist assistance patrols), cameras monitoring roads, and the availability of E911 service, and cell phones have made the call boxes less important in helping travelers report incidents that do occur. Consequently, FDOT is in the process of removing call boxes from many Florida Intrastate Highway System (FIHS) roads. Starting in 2002, the SMS was upgraded from an analog, non-integrated system to a digital backbone to create a seamless and homogenous statewide monitoring system, which was intended to primarily support traveler information and hurricane evacuation services. For iFlorida project, FDOT decided to use the SMS to support the transmission of multiple streams of IP-based traffic information from remote field devices to Regional Traffic Management Centers (RTMC) that were connected to the microwave system data network. FDOT’s experience with the use of SMS network for statewide monitoring offers a number of lessons learned as presented below.
  • Design traffic video transmission systems around the constraints of limited bandwidth availability. The FDOT SMS network consists of a set of hub sites with fiber connection and remote sites using microwave to communicate with the hub sites. The remote sites are daisy-chained, so that bandwidth usage at the remote site nearest the hub is the sum of the bandwidth required for that site and for all other remote sites directly or indirectly connected to it. This network is capable of transmitting up to 33 megabits per second (Mbps) between hub sites and up to 3 Mbps from remote sites to hub sites. One of the challenges faced in designing the Statewide Monitoring System to use the SMS was the limited bandwidth available and the relatively high bandwidth requirements of traffic video. The exhibit below lists the approximate bandwidth required for different types of video using different types of compression.
    Approximate Bandwidth Requirements for Traffic Video
    Resolution
    MPEG-2
    MPEG-4
    Low
    Medium
    High
    Low
    Medium
    High
    QCIF
    0.34
    0.24
    0.14
    0.17
    0.12
    0.07
    CIF
    1.01
    0.62
    0.38
    0.50
    0.31
    0.19
    4CIF
    2.88
    1.92
    1.10
    1.44
    0.96
    0.55
    Mbps = Megabits per second. QCIF = Quarter Common Intermediate Format (176 pixels by 144 lines, 30 frames per second; 1.22:1).
    CIF = Common Intermediate Format (352 pixels by 288 lines, 30 frames per second; 1.22:1).
    4CIF = 4 times Common Intermediate Format (704x576 pixels).
    Source: Table 13, Source Document.
    Given that the bandwidth available from remote sites to hub sites was limited to 3 Mbps and part of this bandwidth was reserved for other applications, FDOT determined that it could deploy, at most, three monitoring sites along a single "spoke" of remote microwave towers. The first step taken by FDOT in designing this system was to review the network topology for the microwave network to identify the remote towers that shared a single spoke. This allowed FDOT to select Statewide Monitoring System sites so that no more than three sites lay along the same spoke before reaching a hub site.
  • Provide provisions for remote configuration of the video compression hardware in designing traffic video transmission systems. FDOT also required that each site include video compression hardware that was remotely configurable. This allowed FDOT to easily vary the video type and compression after the system was deployed in order to find the combination that worked best with the limited bandwidth available through the SMS. At the time of this report, FDOT was using MPEG-4 with CIF resolution and low compression for an expected bandwidth usage of about 500 kilobits per second per camera. The resulting video appears slightly grainy on a full screen and slightly choppy. FDOT felt that the video was definitely of high enough quality to support traffic management decision making, though the quality was noticeably lower than most other video that FDOT D5 has available.
  • Beware of trade off between cost savings from using an existing SMS network and the network’s capability to support essential functions. Florida’s Statewide Monitoring System demonstrated that using the pre-existing microwave communication network was a cost-effective approach for providing communications to remote traffic monitoring stations. FDOT noted that the network was reliable, except for some disruptions during bad weather. FDOT also noted that using the locations of microwave towers as the primary factor in selecting sites for the Statewide Monitoring System might have been a mistake. A better system may have resulted from selecting sites primarily on the basis of the usefulness of the sites for supporting transportation decision making, and only taking advantage of microwave tower locations when consistent with those site selections.
It is prudent to consider cost savings while also achieving the optimum functionality in ITS deployment. Lessons from Florida’s experience with using an SMS network offers guidance on how to design around external constraints, such as bandwidth capacity, so that a desired statewide monitoring system performs essential functions of transmitting traffic video to traffic management center to help improve operational efficiency and mobility.


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Source

iFlorida Model Deployment Final Evaluation Report

Author: Robert Haas (SAC); Mark Carter (SAIC); Eric Perry (SAIC); Jeff Trombly (SAIC); Elisabeth Bedsole (SAIC): Rich Margiotta (Cambridge Systematics)

Published By: United States Department of Transportation Federal Highway Administration 1200 New Jersey Avenue, SE Washington, DC 20590

Source Date: 01/30/2009

EDL Number: 14480

URL: http://ntl.bts.gov/lib/31000/31000/31051/14480.htm

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Lessons From This Source

Assess security risks, threats, vulnerabilities, and identify countermeasures to ensure operations of transportation management centers.

Be flexible to use data from various sources, such as the highway police patrol’s incident data, user feedback, and monitoring stations, to develop a statewide traveler information system.

Beware of challenges involved in developing an integrated statewide operations system for traffic monitoring, incident data capture, weather information, and traveler information—all seamlessly controlled by a central software system.

Beware of costs, utility, reliability, and maintenance issues in deploying a statewide transportation network monitoring system.

Beware of the limitations of using toll tags in order to calculate travel time on limited access roadways and arterials.

Beware that software development for ITS projects can be utterly complex, which demands avoiding pitfalls by following a rigorous systems engineering process.

Define a vision for software operations upfront and follow sound systems engineering practices for successfully deploying a complex software system.

Deploy a variable speed limit system only after the software systems required to support it are mature and reliable.

Design traffic video transmission systems around the constraints of bandwidth limitations and provide provisions for remote configuration of video compression hardware.

Develop an accurate, map-based fiber network inventory and engage ITS team in the construction approval process.

Develop an effective evacuation plan for special event that gathers a large audience and consider co-locating the responding agencies in a joint command center.

Ensure compatibility of data format of the field-weather monitoring sensors with the central software in the transportation management center.

Ensure that experienced staff oversee the development of a complex software system and thoroughly follow systems engineering process.

Ensure that Highway Patrol's CAD system operators enter key information needed by the transportation management center operators.

Establish a well defined process for monitoring and maintenance before expanding the base of field equipment.

Estimate life-cycle cost of ITS technologies as part of procurement estimates in order to assess the range of yearly maintenance costs.

In developing software for automated posting of messages on dynamic message signs, focus on the types of messages that are used often and changed frequently, and also include manual methods for posting.

Incorporate diagnostic tools to identify and verify problems in the transmission of video in a transit bus security system.

Perform adequate analyses and tests to design, calibrate and validate the capabilities of a bridge security monitoring system in order to reduce false alarms.

To support statewide traveler information services, design and implement reliable interface software processes to capture incident data from the local and highway patrol police’s computer aided dispatch systems.

Use simple menu choices for 511 traveler information and realize that the majority of callers are seeking en route information while already encountering congestion.

States

Florida

Countries

United States

Goal Areas

Mobility
Efficiency

Keywords

CCTV, closed circuit television cameras, road monitoring, sensors, vehicle detector, traffic detection, traffic monitoring, congestion monitoring

Lesson ID: 2010-00549