Homework 6 Solutions

(1) For a 35 mph approach, show how you would use detector information and signal status to estimate average delay as a performance measure. Refer to the ITD manual for the detector drawing. Use a time-space diagram to illustrate how the method you propose would work. Use the same diagram to show weaknesses and assumptions that you have to make. Clearly state how each detector will be used to collect the data that you need.

Used US 12 and 3rd Street NB approach.

Links 1000014 and 5. Only link 1000014 data are used.

Start time: 70.1 (sim sec)End time: 135.1 (sim sec)

Begin red: 70.1 (sim sec)Begin green: 92.2 (sim sec)End green: 135.1 (sim sec)

Measuring delay across both lanes, so arrivals and departures can be counted in both lanes at once.

Stop bar is at link coordinate 319.4 ft (this is the 0 ft reference point for detectors)

**detector location specified in terms of detector downstream edge**

Stop bar Detectors are between -3 ft and 19 ft relative to the stop bar take departure count at farthest downstream stop bar loop at 0 ftMiddle detectors at 79 ft relative to stop barUpstream detectors at 181 ft relative to stop bar (take arrival count at these detectors)

Count intervals: 10 seconds

For this delay measurement example, I started counting at t = 70 seconds. There was already one vehicle between the two detectors. This represents two weaknesses of this method for measuring delay. One is that driveways that introduce or remove vehicles between the detectors will throw the delay measurement off. Another is that when you start measuring you have to either assume that there are no vehicles between the detectors or you have to count the vehicles between them. I assumed no vehicles between the detectors. The effect of this assumption is a delay measure that is biased low.

Each detector counts the cars that traverse them and the count data are reported back to the controller which then sums the counts, cumulatively, by interval.

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35070 80 90 100 110 120 130 140

Simulation Time (sec)

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Stop bar count location

Upstreamcount location

Cummulative Departure Count

Cummulative Arrival Count

(2) For a 25 mph approach, show how you would use detector information and signal status to estimate wasted green time as a performance measure. Refer to the ITD manual for the detector drawing. Clearly state how each detector will be used to collect the data that you need. Show an example calculation that includes each detection, signal status, and condition you need to know in order to arrive at your wasted green time estimate.

Wasted green time is the portion of green time for an active phase that is not used to serve vehicles. Therefore, this portion of green time is wasted. One way to calculate the wasted green time is to divide a green time into sub-intervals. The length of sub-intervals is user-defined, e.g., two seconds.  A used sub-interval is an interval during which the stop-bar detector has been occupied. On the other hand, a wasted sub-interval is one during which the stop bar detector is not occupied. The sum of the length of all wasted sub-intervals is the duration of wasted green time for a green time. The figure below shows a green time interval and the time during which the stop bar detector is occupied (patched pattern).  The length of the green time is 11 seconds. The sub-interval is defined to be 3 seconds. Therefore, this green time interval can be divided into three intervals and one residue interval of two seconds. The first and second intervals are used. So the wasted green time is three seconds if the residue interval is not counted.

Therefore, the percentage of wasted green time is the ratio between the duration of wasted green time and the total green time. For the above example, the percentage of wasted green time is 3 seconds divided by 11 seconds, i.e., 0.27.On Figure 306.05-02 Loop Detector Spacing Plan in ITD Traffic Manual, stop bar detectors are used for all approach speeds. These stop bar detectors and green time information (the start and end of green time) can be used to calculate wasted green time.

(3) Refer to the MUTCD to answer the following questions:

a. When should pedestrian signals be used?

Standard: Pedestrian signal heads shall be used in conjunction with vehicular traffic control signals under any of the following conditions:

A. If a traffic control signal is justified by an engineering study and meets either Warrant 4, Pedestrian Volume or Warrant 5, School Crossing (see Chapter 4C);

B. If an exclusive signal phase is provided or made available for pedestrian movements in one or more directions, with all conflicting vehicular movements being stopped; or

C. At an established school crossing at any signalized location.D. Where engineering judgment determines that multiphase signal indications (as

with split-phase timing) would tend to confuse or cause conflicts with pedestrians using a crosswalk guided only by vehicular signal indications.

Guidance:Pedestrian signal heads should be used under any of the following conditions:

A. If it is necessary to assist pedestrians in making a reasonably safe crossing or if engineering judgment determines that pedestrian signal heads are justified to minimize vehicle-pedestrian conflicts;

B. If pedestrians are permitted to cross a portion of a street, such as to or from a median of sufficient width for pedestrians to wait, during a particular interval but are not permitted to cross the remainder of the street during any part of the same interval; and/or

C. If no vehicular signal indications are visible to pedestrians, or if the vehicular signal indications that are visible to pedestrians starting or continuing a crossing provide insufficient guidance for them to decide when it is reasonably safe to cross, such as on one-way streets, at T-intersections, or at multiphase signal operations.

b. At what point in the pedestrian phase should each interval (steady “WALK”, flashing “DON’T WALK”, and steady “DON’T WALK”) appear? Include a description of when it should appear relative to the non-conflicting vehicle phase.

Standard:When pedestrian signal heads are used, a WALKING PERSON (symbolizing WALK)

signal indication shall be displayed only when pedestrians are permitted to leave the curb or shoulder.

A pedestrian clearance time shall begin immediately following the WALKING PERSON (symbolizing WALK) signal indication. The first portion of the pedestrian clearance time shall consist of a pedestrian change interval during which a flashing UPRAISED HAND (symbolizing DONT WALK) signal indication shall be displayed. The remaining portions shall consist of the yellow change interval and any red clearance interval (prior to a conflicting green being displayed), during which a flashing or steady UPRAISED HAND (symbolizing DONT WALK) signal indication shall be displayed.

If countdown pedestrian signals are used, a steady UPRAISED HAND (symbolizing DONT WALK) signal indication shall be displayed during the yellow change interval and any red clearance interval (prior to a conflicting green being displayed) (see Section 4E.07).

At intersections equipped with pedestrian signal heads, the pedestrian signal indications shall be displayed except when the vehicular traffic control signal is being operated in the flashing mode. At those times, the pedestrian signal lenses shall not be illuminated.

Guidance:Except as noted in the Option, the walk interval should be at least 7 seconds in length so that pedestrians will have adequate opportunity to leave the curb or shoulder before the pedestrian clearance time begins.

Option:If pedestrian volumes and characteristics do not require a 7-second walk interval, walk intervals as short as 4 seconds may be used.

Support:The walk interval itself need not equal or exceed the pedestrian clearance time calculated for the roadway width, because many pedestrians will complete their crossing during the pedestrian clearance time.

Guidance:The pedestrian clearance time should be sufficient to allow a pedestrian crossing in the crosswalk who left the curb or shoulder during the WALKING PERSON (symbolizing WALK) signal indication to travel at a walking speed of 1.2 m (4 ft) per second, to at least the far side of the traveled way or to a median of sufficient width for pedestrians to wait. Where pedestrians who walk slower than 1.2 m (4 ft) per second, or pedestrians who use wheelchairs, routinely use the crosswalk, a walking speed of less than 1.2 m (4 ft) per second should be considered in determining the pedestrian clearance time.

Option:Passive pedestrian detection equipment, which can detect pedestrians who need more time to complete their crossing and can extend the length of the pedestrian clearance time

for that particular cycle, may be used in order to avoid using a lower walking speed to determine the pedestrian clearance time.

Guidance:Where the pedestrian clearance time is sufficient only for crossing from the curb or shoulder to a median of sufficient width for pedestrians to wait, additional measures should be considered, such as median-mounted pedestrian signals or additional signing.

Option:The pedestrian clearance time may be entirely contained within the vehicular green interval, or may be entirely contained within the vehicular green and yellow change intervals.

On a street with a median of sufficient width for pedestrians to wait, a pedestrian clearance time that allows the pedestrian to cross only from the curb or shoulder to the median may be provided.

During the transition into preemption, the walk interval and the pedestrian change interval may be shortened or omitted as described in Section 4D.13.

c. Where should you locate the pedestrian button?

Standard:Pedestrian signal heads shall be mounted with the bottom of the signal housing including brackets not less than 2.1 m (7 ft) nor more than 3 m (10 ft) above sidewalk level, and shall be positioned and adjusted to provide maximum visibility at the beginning of the controlled crosswalk.

If pedestrian signal heads are mounted on the same support as vehicular signal heads, there shall be a physical separation between them.

d. In your own words, explain the guidelines for timing each pedestrian interval. Give an example calculation for the pedestrian phase crossing SH 8 at the intersection of Farm Rd and SH 8. Use Google Earth to get the necessary measurements.

WALK (steady): from 4 to 7 seconds…depending on pedestrian volumeDON’T WALK (flashing): at least equal to (traveled way width or distance to median)/4 fps. Can extend into the yellow clearance interval and/or red clearance interval .DON’T WALK (steady): remaining portion of the yellow clearance interval and red clearance interval during which the flashing-DON’T WALK is not active.

(4) Time the YELLOW and ALL-RED intervals for the EBTH and EBLT movements for the same intersection as used in problem 3 (above). For the necessary distance measurements, refer to Google Earth. Use the posted speed as the design vehicle speed.

For the through movement.