System Requirements
Safe Intersections Systems
Minnesota Department of Transportation
Mn/DOT Contract No. 94260
Short Elliott Hendrickson Inc.
MNTMD 112619
October 2011
1. Project Description
1.1. The Safe Intersections Systems project will develop and field deploy five intersection
collision warning (ICW) systems using commercial off the shelf (COTS) products, to
provide active, real-time supplemental warning to drivers approaching an intersection
and alert them to look for traffic at or approaching the intersection. The intent of the
ICW project is to develop a safe and effective low-cost system that can be readily
deployed in rural areas and is easy to operate and maintain.
1.2. The project will follow traditional systems engineering principles to provide for
stakeholder input, requirements definition, detailed system design, laboratory testing and
field operational testing phases. A multi-organizational project team will provide input
throughout the project. The project will be delivered over a 30 month time frame from
July 2010 to December 2013. System installations are anticipated to occur during the fall
of 2011. A project evaluation will be conducted to capture data on the effectiveness of
the ICW systems.
1.3. An integral part of the development process for the ICW systems is the creation of
System Requirements. The System Requirements listed below along with the Concept
of Operations document will provide the basis for the Detailed System Design effort for
the project.
2. Functional Requirements
2.1. Each system shall use detection devices to detect the speed and/or location of vehicles
approaching the intersection on the major roadway.
2.2. Each system shall use detection devices to detect the presence of vehicles on the minor
roadway at the intersection.
2.3. Consideration shall be given to the use of detection devices to detect vehicles on the
minor roadway approaching the intersection.
2.4. Each system shall communicate the detection information that will activate dynamic
warning signs and/or devices.
2.5. The warning sign and/or device shall provide active real-time warning to minor roadway
drivers at the intersection and major roadway drivers approaching the intersection. The
intent of the warning sign and/or device is that its meaning will be intuitive to the driver.
2.6. The warning shall alert minor roadway drivers to look for approaching major roadway
traffic either to the left, right, or both and shall alert major roadway drivers of the
presence of minor roadway vehicles at the intersection.
2.7. The warning sign shall either conform to the Minnesota Manual on Uniform Traffic
Control Devices (MN MUTCD), Part 2C as it relates to warning signs, or a request to
experiment shall be prepared and approved for a warning sign that does not conform to
the MN MUTCD.
3. Performance Requirements
3.1. Expandability: The system shall accommodate the major and minor roadway detection
and warning needs for up to a 4-leg intersection. As traffic grows, the system must be
able to handle increased volumes of users and/or data.
3.2. Speed: The end-to-end response time of the system shall be less than 500 milliseconds
(ms). For vehicles within the defined detection envelope of the system; the system will
detect the vehicle, process signals, and communicate to the warning sign node within
500ms.
3.3. Safety: The intersection warning system shall not obscure or detract from any in place
signing. The system shall be able to meet NCHRP 350 certification if needed.
3.4. Reliability: The system shall detect approaching major roadway traffic with less than a
2.5% error and predict arrival at the intersection. The system shall detect minor roadway
traffic at the intersection and if used, minor roadway traffic approaching the intersection
with less than a 2.5% error.
3.5. Availability: The system is intended for 24 hour per day, 7 day per week continuous
operation. The system shall function with a 99 % up-time.
3.6. Maintainability:
3.6.1. Hardware Maintenance: All system hardware components shall be self-contained
commercial off the shelf (COTS) modules housed in weather proof, NEMA 4 rated
enclosures suitable for outdoor use. No internal manual settings or adjustments
shall be needed to install or maintain the system. Maintenance shall consist of
module-level replacement and shall not require circuit board level or componentlevel adjustment, replacement or repair.
3.6.2. Software Set up, Programming and Diagnostics: The system shall be user
programmable through the use the individual component or a laptop computer and
shall allow for diagnostics, data download and programming of system parameters.
The system shall allow operations staff to perform diagnostics via the individual
component or a laptop connection.
3.7. Failsafe mode: The failed system shall not present a more dangerous situation than if the
system was not present at the intersection.
3.8. Fault detection: The system shall employ a fault detection component for easily
determining the proper functioning of the system.
4. Operational Requirements / Operational Modes
4.1. Normal Operation: During normal operating conditions the ICW system shall actively
detect the presence of traffic approaching the intersection on the major roadway and the
presence of traffic at the intersection on the minor roadway. It may be necessary to
detect traffic approaching the intersection on the minor roadway to achieve operational
requirements of the system. When the presence of a vehicle is detected on the major
roadway, approaching from either direction or from both directions simultaneously, this
information is used to activate the warning sign, which is viewed by the driver on the
minor roadway at the intersection. The activated warning will alert the minor roadway
driver to the presence of approaching traffic on the major roadway. The indication will
be displayed for a duration that corresponds to the calculated time needed for the
approaching vehicle(s) to proceed to the intersection, or for a pre set amount of time
based on distance from the intersection. When the presence of a vehicle is detected on
the minor roadway, this information is used to activate a warning, which is viewed by
the driver on the major roadway, approaching the intersection. The activated warning
will alert the major roadway driver to the presence of traffic on the minor roadway at or
possibly approaching the intersection. The indication will be displayed until the minor
roadway vehicle is no longer at the intersection. When no vehicles are detected the ICW
system shall remain in its normal unactivated state, with no active warning indication
being given that approaching vehicles are present
4.2. Fault Operation: The system shall provide a means for determining that the system is
not operational. When a fault condition occurs, the system shall create an internal fault
notification and cause the system to provide an indication on the warning sign/device
that is unique from any other operation mode. Fault conditions may include: 1. Loss of
communication between nodes of the system, 2. Malfunction of detection, 3. Failure of
warning sign/device (indication), 4. Low power or loss of power.
4.3. Diagnostic Operation: The system shall permit operations staff to monitor operation of
all system components. This monitoring shall be accessible at a central node or all
nodes of the system and shall display system status in real time.
5. Interface and Subsystem Requirements
5.1. Detection: The ICW system shall use detection devices necessary to operate the
systems. These devices may include detection of approaching vehicles, speed of
vehicles, presence of vehicles, etc. Detectors shall have less than 2.5% error in vehicle
volumes and less than 0.5 mph in vehicle speeds.
5.2. Warning Devices: Warning sign(s) shall provide notification to the minor roadway
driver of approaching major roadway vehicle(s). Warning sign(s)/devices shall provided
notification to the major roadway driver of minor roadway vehicles at and possibly
approaching the intersection. Signs and devices shall meet all requirements of the MN
MUTCD. The warning message or indication given to the driver shall be intuitively
obvious to understand. Placement of the warning sign shall be on the far side of the
intersection within the minor roadway driver’s cone of vision. The size of the warning
sign shall be such that can be easily seen by the minor roadway driver(s). Placement of
the warning device on the major roadway, shall be in advance of or at the intersection.
5.3. Power: The system shall be powered by the AC power or a solar panel, with battery
backup. If solar powered, the battery system shall function for a reasonable amount of
time in the event of loss of solar charging. The system design shall minimize power
consumption to allow for the smallest possible panel size. When placing solar panel, it
must have a clear view of the southern sky. Placement in areas with heavy foliage that
blocks the panel’s openness to the sun will affect how long the system can operate
without manual recharge or replacement of the primary battery. Traffic volumes at each
selected site will affect battery and panel size. Some sites with high traffic volumes or
obscured southern view of the sky may require AC power or frequent battery recharging.
5.4. Environmental Requirements: The system shall function to defined requirements in
typical Minnesota weather conditions. The Operating Temperature Range shall be: -34°
to +74° C.
5.5. Communications: Communication links shall automatically establish and maintain
connection between detection nodes and the warning sign node. Wireless
communication between the nodes of the system shall occur via a secure wireless link.
Wireless connection shall perform in heavy rain and snow conditions up to and including
3 inches per hour rainfall.
6. Data Requirements
6.1. Data Content: The system shall monitor and record system performance. The data shall
be retained within the system, on-board for a period of 7 days, or the maximum number
of events allowed by the COTS controller. The system shall retain individual events
with a time stamped record for each event. The system shall also keep a daily running
total (i.e tallies) of system events. Tallied data totals shall be available via wireless
laptop access to the system and/or by removal and access of the memory card. The time
stamped event data shall only be available through removal and access of the memory
card. The systems shall record system events such as: Vehicle detected by node;
Speed at time of detection; Time of detection used for validation; Status – Warning On,
Warning Off, Fault – Enter, Recovery from fault, and System Restart.
6.2. Data Record Frequency
6.2.1. For each Event (such as vehicle detections, warning on, warning off, etc)
6.2.2. Heartbeat record in absence of events
6.2.3. Communications loss
6.3. Data Archive and Retrieval: Data shall be maintained in individual nodes and shall be
accessible from the central node during service operations. The system shall continue to
operate during data collection and downloading.
7. Enabling Requirements
7.1. Road Geometry and Volume: The ICW system shall be suitable for installation on
roadways that have a two- lane, two-way geometry. The ICW system detectors are not
intended for roadways with more than one through lane in either direction.
7.2. Roadway Volume: If the ICW system is designed to operate on solar power the solar
system shall be sized to accommodate detections based on the intersections traffic
volumes.
7.3. Installation: The system shall be easy to deploy. Installation of this system shall require
a minimum of infrastructure to make the system operational.
7.4. Parts / Materials / Components: The components of the system shall be standard
commercial off the shelf (COTS), field proven devices.
7.5. The system shall comply with FCC emission requirements. The system shall be able to
meet needed FCC approvals when design is complete.
7.6. System Costs: The system shall be considered low cost.
8. Test and Evaluation Requirements
8.1. System data shall be provided in a readily usable format.
8.2. System data shall be downloadable.
8.3. System data shall be retained for 7 days or the maximum number of events allowed by
the COTS controller.
8.4. System data shall be individually time stamped. System clocks shall be synchronized
and maintained to within +/- 2 seconds.
8.5. System data shall include:
8.5.1. Fault type
8.5.1.1.
Loss of radio communication between nodes of the system
8.5.1.2.
Malfunction of detector nodes
8.5.1.3.
Failure of warning sign/device (indication)
8.5.1.4.
Low power or loss of power
8.5.2. Vehicle detection
8.5.3. Vehicle speed
8.5.4. System activation
8.5.5. System deactivation
8.5.6. Fault – enter
8.5.7. Fault – recovery
8.5.8. System restart