An open and shut case

Traffic signalization, ITS helps traffic deal with bascule bridges

Marc Start, P.E., Robert Clegg, P.E., Contributing Authors / November 13, 2003

Located on the shores of the St. Clair River, the downtown
area of Port Huron, Mich., is divided by the Black River, and three closely
spaced bascule bridges link the north and south shores. The next bridge over
the Black River is located about five miles inland.

Getting around in Port Huron can be a challenge,
particularly in the summer months. Recreational boats make up a high percentage
of the river traffic, and the bascule bridges are raised roughly on the
1/2 hour during the peak summer days. The most active bascule bridge,
Military Street, is on a state highway carrying 19,000 vehicles a day, and on
the average day there are 25 bridge events (raising and lowering). Two other
bascule bridges, 7th Street and 10th Street, are under the jurisdiction of the
city. Each bridge event lasts about six minutes and can create a significant
amount of traffic congestion, especially during the summer tourist season. City
police and fire services also are impacted during the boating season.

The city of Port Huron staff recognized the challenges of
traffic control with the bascule bridges, and successfully submitted an
application for Congestion Mitigation and Air Quality (CMAQ) funding of a
traffic signal modernization and interconnect project. The goals of the project
are to reduce traffic congestion related to the bridge events and to reduce
city emergency service response times.

The city developed a consultant request for proposals to
define the scope of the project. URS Corp., Grand Rapids, Mich., was selected
to design the traffic signal system comprising 21 traffic signal installations,
optimize the traffic signal timings and provide limited construction inspection

Project opportunities

There were several key opportunities to effectively divert
traffic and emergency vehicles from one bridge to another upon a bridge
raising. The project took advantage of the following:

* The city had a licensed radio frequency available, which
was desirable to provide communications for the traffic signal system;

* The Municipal Office Center is centrally located in the
city, providing a potential broadcast point for the wireless communications
system to serve both sides of the river. The Municipal Office Center also was
the logical location for the central computer that operated and monitored the
traffic signal system; and

* The street configuration of the downtown area allows for
efficient traffic diversion, minimizing the travel time and distance needed to
bypass a raised bridge to use an available bridge.

ITS applications

Several types of information would reduce motorist delay and
emergency response times, all utilizing the traffic signal system as a
communications link. The intelligent transportation systems applications are as

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* Fire station: The fire station, located on the north bank
of the Black River, would benefit from knowing when a bascule bridge is raised
so that fire trucks do not travel toward a closed bridge. A light panel by the
garage door in the fire station representing the three bridges will notify fire
personnel about the status of the bridges. The light panel is automatically
activated by the bascule bridge raising sequence;

* Police dispatch: The police dispatch office, located in
the Municipal Office Center, would benefit from knowing when a bascule bridge
is raised so that emergency vehicles do not travel toward a closed bridge. A
light panel in the police dispatch office representing the three bridges will
notify police dispatch about the status of the bridges;

* Bascule bridge houses: The bascule bridge houses would
benefit from knowing when a fire truck has just left the fire station so that a
bridge is not raised immediately prior to a fire truck's arrival at a bridge.
An indicator light was added to the three bridge houses so that the bridge
operators would be forewarned of an approaching fire truck; and

* Signal timing modifications during bridge openings:
Traffic signal timings at intersections surrounding the bascule bridges will
change during a bridge event in order to facilitate the natural flow of traffic
away from the bridge out of service. Motorist information may be added at a
later time using dynamic message signs or static signs with flashers.

Design issues

In the design phase of the project, several issues were
addressed that impacted the effectiveness and reliability of the traffic signal
operations, now and in the future. The most significant issues were as follows:

* With the modernized traffic signal installations, the
traffic signals were arranged in a box configuration, which is a deviation from
the typical diagonal configuration usually found in Michigan. The box
configuration provides greater visibility to motorists and ease of maintenance;

* The wireless communications system serving the traffic
signal system must be reliable and isolated from interference, since police
dispatch and emergency response services are dependent on the information
transmitted by the traffic signal system. The licensed frequency already owned
by the city mitigated this issue;

* Although the city's traffic signal system and the MDOT
traffic signal system are located in the same general area, using a common
master controller to govern both traffic signal systems was not desired.
However, the two traffic signal systems can be synchronized so that they will
operate in a manner similar to having a common master controller; and style="mso-spacerun: yes">

* The underground handholes supporting the traffic signal
installations were sized properly to support a future upgrade to fiber-optic
communications, if desired.

Construction phase

City staff provided contract administration and day-to-day
inspection during construction, with URS providing technical assistance. The
city's master electrician programmed the traffic controllers in accordance with
URS timing plans. Construction will be completed by the end of 2003.

The total project cost was approximately $1.2 million, and
the city of Port Huron received a CMAQ grant totaling $925,000. The contractor
bid for the project was $998,000. This included 17 traffic signal installation
modernizations, communications upgrades to four existing traffic signal installations,
a computer workstation with traffic signal control software and communication
links to 21 traffic signals, three bridge houses, one fire station and the
Municipal Office Center.

The traffic signal timings at the intersections surrounding
the Black River will change upon a bridge raising event to accommodate traffic
diverting from the path toward the raised bridge.

The licensed frequency will be used for the wireless traffic
signal communications system. The traffic signal system also can accommodate a
future opportunity to actively assist motorists by providing bridge status
information via dynamic message signs or static signs with flashers.

About the Author

Start is a senior traffic engineer for URS Corp., Grand Rapids, Mich. Clegg is the Port Huron City Engineer and Director of Public Works.

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