Exhibit 5-3 Illinois Tollway ITS w/I-PASS Acct. Status Lights and E-470 ITS w/Violation Alarm & Light (right)
Island Traffic Signal Design Issues
The diameter of signal head used to assemble the ITS must be selected to be consistent in scale and form with other toll lane equipment such as the patron fare display, and be clearly visible to approaching passenger car and truck traffic without excessive brightness, and provide the most economical solution relative to capital and maintenance costs.
The location of the ITS must be selected to assure visibility to approaching passenger car and truck traffic while preventing the displayed signal state intended for the paid exiting vehicle to also be viewed and interpreted as the correct state for a following vehicle approaching or at the toll collection point. The implementation of ETC capability in the lane increases the potential for confusion because the majority of time a leading ETC equipped vehicle will receive a quick green signal allowing an immediate exit from the lane but potentially leaving the green signal in full view for the following vehicle that is not ETC equipped.
The location of the ITS is constrained by the physical features of the toll island, such as the size and shape of tollbooth and columns supporting the canopy as well as the length of departure end of the toll island. Similarly, the location of other toll collection equipment, particularly a patron toll display and an automatic barrier gate, limit locations available for installing the ITS.
Adequate horizontal clearance from the vertical face of the toll island or raised barrier must be provided to avoid damage from passing vehicles.
Similar to the location of the ITS, the height of the ITS also needs to be designed to assure visibility to approaching passenger car and truck traffic.
Island Traffic Signal Guideline Development:
The two most common diameters used for traffic signal heads are 12 inches and 8 inches. Consistent with the survey results, the 8-inch diameter signal is predominantly used in existing agency toll lanes. This diameter uses less of the limited toll island space and is more consistent in scale and form with the patron fare display, thereby avoiding domination of the user’s focus upon entering the toll lane. Of the two types of traffic signal heads that can be installed in a toll lane, LED or incandescent lamp, the LED signal clearly has a lower life cycle cost based on energy consumption and lamp replacement costs. Because the LED signal head provides significantly higher nighttime intensity relative to a lamp signal head it may be deemed undesirable. However, toll lane lighting can be designed to mitigate the high intensity affects of the LED signal heads.
The location of the ITS on the toll island is first dependent on the location of any canopy column and any automatic barrier gate. The next consideration is installing the ITS in a location where the window of time that the ITS is within full view of an exiting vehicle is balanced with the ability to display the intended signal state to the following vehicle before the vehicle reaches the toll collection point. Assuming an arming or presence loop is installed at the toll collection point, a practical solution is one that uses the falling signal from the trailing edge of the loop, effectively functioning as a trigger to the lane software to change the state of the ITS. Based on this analysis, the ITS should be installed approximately 15 feet beyond the downstream edge of the loop, assuming 15 feet represents the detection length of a typical vehicle and there are no physical constraints to this location. Visibility issues with the ITS can primarily be resolved by selecting the optimum height of the assembly for viewing by both passenger car and truck users. Although not preferred or recommended, some agencies combine the ITS and automatic barrier gate cabinet or install the ITS immediately behind the cabinet. Separate installations, with the ITS installed in front of the gate, avoids the potential temporary loss of both components resulting from a vehicle collision and ITS visibility loss from a raised gate arm. With 6-18 inches representing a conservative range for horizontal clearance from the travelway used within the toll industry, a recommended clearance of 12 inches provides the same protec-tion afforded the tollbooth for a location where the vehicle is expected to have maneuvered to the center of the lane in the course of exiting the plaza. The height of the ITS should be uniform for all toll lanes to minimize pedestal spare parts or the need to custom cut pedestals. The survey results indicate a predominant height of approximately 4 to 5 feet. This height is expected to assure visibility to approaching passenger car and truck traffic under most conditions.
|Guideline||Island Traffic Signal Design Guideline 1|
|Title||ITS Signal Size|
|Text||Subject to other unique toll plaza considerations, the ITS should consist of 8 inch diameter, LED traffic signal heads.|
|Guideline||Island Traffic Signal Design Guideline 2|
|Text||The ITS should be installed approximately 15 feet beyond the downstream edge of the presence or arming loop.|
This location assumes 15 feet represents the detection length of a typical vehicle, the installation of a presence loop at the collection point, and there are no physical constraints to this location. Otherwise, alternative locations should be considered and field tested.
|Guideline||Island Traffic Signal Design Guideline 3|
|Title||ITS Horizontal Clearance|
|Text||A horizontal clearance of 12 inches should be used from the face of the toll island or raised barrier to the nearest edge of the ITS signal head.|
|Guideline||Island Traffic Signal Design Guideline 4|
|Text||Subject to the known or forecasted traffic mix, the height to the bottom of all ITS should be in the range of 4 to 5 feet.|
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