Users include motorists, bicyclists, and pedestrians within the highway, including persons with disabilities, defined by the Americans with Disabilities Act of ADA. The design phase of a project considers accommodating pedestrians through or around the work zone. The contractor is responsible for accommodating pedestrians through or around the work zone. These Standard Specifications sections apply to pedestrian facilities:.
At the preconstruction conference, discuss the need for temporary pedestrian facilities and ADA requirements. When planning for pedestrians in work zones, verify that the contractor does the following items:. When existing pedestrian facilities are disrupted, closed, or relocated, the temporary facilities should be detectable and include accessibility features consistent with those in the existing pedestrian facility.
If the pedestrian facility existing before construction began was accessible to pedestrians with disabilities, the one provided during construction should also be accessible. Do not sever or move a pedestrian route for nonconstruction activities such as parking for vehicles and equipment. Maintain a width of 60 inches throughout the length of the pedestrian pathway.
The path must have a clear width of no less than 48 inches. Verify that no fixed objects cabinets, poles, and so forth will reduce the path width at any point. The path must be stable, firm, and slip resistant. Pedestrian facilities must be surfaced with asphalt concrete, portland cement concrete, or timber. Dirt is not an acceptable surface. The cross slope must be no greater than 2 percent and the running slope no greater than 5 percent.
Signs and other devices mounted lower than 7 feet above the temporary pedestrian pathway should not project more than 4 inches into accessible pedestrian facilities. Refer to Part 6, Section 6D. Place a barrier across the full width of a closed sidewalk. A person with a visual disability traveling with the aid of a long cane should be able to detect it.
Unless the contractor can provide a reasonably safe route that does not involve crossing the roadway, use appropriate advance signing to direct pedestrians to cross to the opposite side of the roadway. In urban and suburban areas with high vehicular traffic volumes, place the signs at intersections.
Midblock worksites should not cause pedestrians to skirt the worksite or make a midblock crossing. Consider separating pedestrian movements from both job site activity and vehicular traffic. When pedestrians are routed adjacent to live traffic, provide barrier protection to prevent vehicles from entering the pedestrian facility.
Do not use tape, rope, or plastic chain strung between devices as controls for pedestrian movements. They are not detectable by persons with visual disabilities. Verify that the contractor constructs permanent new facilities and alterations to existing facilities in accordance with the contract plans and specifications.
If a change order is needed to add a permanent facility, contact the district Design Unit to develop plans. During the inspection process, check that all contractor-installed finished elements comply with dimensions and installation requirements. Do not exceed the maximums shown in the requirements listed in Section 4. They are absolute. Chapter 1 - Caltrans Construction Organization. Chapter 4 - Construction Details. Chapter 5 - Contract Administration. Chapter 6 - Sampling and Testing. Chapter 7 - Environmental Stewardship.
Chapter 8 - Employment Practices. Chapter 9 - Projects Sponsored by Others. To protect the highway during construction, improvement, or maintenance operations. To protect the highway from damage during storms. Closures may also be necessary for major earthquakes or other natural disasters. Once assigned to the project, do the following: Compare the traffic control plan to site conditions.
Note any unusual local traffic patterns and scheduled special events during the life of the contract. At the preconstruction conference, discuss the traffic control plan with the contractor. If the contractor requests modifications to the contract traffic control plans, refer them to Section Issue a change order for unanticipated conditions or changes to the contract plans or specifications.
Change orders should include traffic control plans in sufficient detail to define all elements of the proposed changes. The district will establish a procedure for preparation, review, and approval of changes related to roadway construction and detour plans that include traffic control devices. Generally, the district traffic operations office is responsible for this review activity. Urgent, unpredictable situations—minor or of short duration—can arise during the work and should be addressed using engineering judgment.
These instances do not require formally approved plans. Maintain written records of orders given and actions taken.
To establish the geometry, markings, devices, and signs that existed during the project, maintain in sufficient detail a record of the placement into service, the changes, and the discontinuance of roadways and detours. Dated notations or revisions to plans may be helpful.
Dated photographs or video recordings, particularly of points of transition, may be especially valuable. If necessary, direct the contractor in writing to act at once to remedy any issue not in compliance with the contract: If the contractor cannot address the traffic safety issue due to lack of materials and it is safe to do so, consider temporarily suspending the work until correction can be made.
If the contractor cannot address the traffic safety issue and it is not safe to suspend the work, request the contractor take all steps necessary to provide for traffic safety and allow only the work that had started at the time the issue was recognized to continue. Consider suspending work for the next shift until a written plan is provided to address future public safety. Call on Caltrans work forces only because of a physical inability of the contractor or a refusal by the contractor to act.
Responsibilities include: Reviewing periodically the traffic control setup for each work zone and discussing any deficiencies with the resident engineer. Serving as a liaison between construction, the district traffic manager DTM and the transportation management plans TMP manager. Reviewing the TMP and traffic contingency plan for constructability issues. Whenever possible, allow traffic to have continued full use of the existing facilities.
When full use is not possible, accommodate traffic by verifying a continuous roadway throughout the length of the project, achieved by using one or a combination of the following: The existing unmodified highway. The newly constructed highway or portions of it. Interim-constructed facilities. A detour where traffic, including pedestrians and bicycles, is diverted over a temporary roadway. Passage of traffic through the work in progress.
Confirm that the temporary roadway is engineered to the same design considerations as those in new construction: Geometrics of alignment and roadway section. Surface of the traveled lanes and shoulders or marginal areas. Pavement markings and other delineations. Barrier and guardrail. Signals and lighting. Pedestrian and bicycle facilities.
Pavement structure. Show the design of the temporary roadway, including pedestrian and bicycle facilities, in the traffic control plan. Verify pedestrian facilities comply with the Americans with Disabilities Act. Make safety and convenience the primary design considerations. Economy will be a factor only as necessary to obtain balance between benefits and resources. By itself, cost should not be a primary limiting factor. The following guidelines are intended only to guide engineering judgment and ingenuity: Create a physical facility that will encourage motorists to appropriately guide their vehicles on the intended path of travel and make it possible for the vehicle to perform as intended.
The traffic lane—the path the car is intended to follow—is a critical element of the roadway. Pavement surface condition, texture, and color. Pavement markers and other delineation. Signals, lighting, and signing.
Try to eliminate surprise elements from temporary roadways. Make the environment like the approach highway. If differences exist, try to make them readily apparent. Collision concentrations and inconvenience may occur with changes in direction, number of lanes, alignment, and speed. Where possible, compensate for a required reduction of one by an improvement of another. For example, compensate for a sharper curve with solutions such as increased lane width or a clear recovery zone.
Application of this concept at a more typical intersection of two-way streets uses the standard ring and barrier structure described in Figure Assignment of phase numbers to signalized intersections is somewhat arbitrary based on historical design principles, but there are some rules that have been applied to standardize operation. Depending on the complexity of the intersection, 2 to 8 phases are typically used, although some controllers can provide up to 40 phases to serve complex intersections or sets of intersections.
Developing an appropriate phasing plan begins with determining the left-turn phasing type at the intersection.
Section 4. There are five options for the left-turn phasing at an intersection: permissive only, protected only, protected-permissive, split phasing, and prohibited. Phasing can have a significant impact on signal system effectiveness for a number of reasons, including:. Permissive only operation requires left-turning drivers to yield to the conflicting vehicle and pedestrian traffic streams before completing the turn. In the permissive mode, the left-turn movement is served concurrently with the adjacent through movement.
Both the left turn and the opposing through movements are presented with a circular green indication. Thus, in this left turn display option, a green arrow is never provided. Permissive operation is primarily used when traffic is light to moderate and sight distance is adequate.
This display option provides the most efficient operation for green allocation at the intersection. The efficiency of this mode is dependent on the availability of gaps in the conflicting streams through which the turn can be safely completed. This mode can have an adverse affect on safety in some situations, such as when the left-turn driver's view of conflicting traffic is restricted or when adequate gaps in traffic are not present.
Figure and the following figures are adapted from those presented in the Signalized Intersections: Informational Guide Report and thus, phase 2 is defined as the eastbound movement.
Protected only operation assigns the right-of-way to drivers turning left at the intersection and allows turns to be made only on a green arrow display. This operation provides for efficient left-turn movement service; however, the added left-turn phase increases the lost time within the cycle length and may increase delay to the other movements. An exclusive left-turn lane is typically provided with this phasing as shown in Figure The left-turn phase is indicated by a green arrow signal indication.
This type operation is recognized to provide the safest left-turn operation. Protected-permissive operation represents a combination of the permissive and protected modes. Left-turning drivers have the right-of-way during the protected left-turn phase. They can also complete the turn "permissively" when the adjacent through movement receives its circular green indication as illustrated in Figure This mode provides for efficient left-turn movement service, often without causing a significant increase in delay to other movements.
This mode also tends to provide a relatively safe left-turn operation, provided that adequate sight distance is available and turns during the permissive component can be safely completed. Protected-permissive phasing should be used with caution when a phasing sequence other than lead-lead left-turn phasing is being deployed. Split phasing represents an assignment of the right-of-way to all movements of a particular approach, followed by all of the movements of the opposing approach.
This is depicted in Figure Spilt phasing may be necessary when intersection geometry results in partially conflicting vehicle paths through the intersections or where the approaches are offset such that left turning vehicles would have to occupy the same space to complete their turns.
Split phasing avoids the conflict of 10 opposing left turn vehicle paths. Similarly, if the intersection has high left turn and through volume, the traffic engineer may have to use shared left turn and through lanes to make efficient use of the approach which would also result in split phasing for the approach. This phasing is typically less efficient than other types of left-turn phasing. It typically increases the cycle length, or if the cycle length is fixed, reduces the time available to the intersecting road.
Prohibition of left turns on an approach is an option that has been implemented in some cases to maintain mobility at an intersection. In some cases, these have been applied only during certain times of day, when gaps in traffic are unavailable and operation of permitted phasing may be unsafe.
Figure is an example from Toronto, Ontario, that prohibits left turns during the morning and evening periods. In general, the operational mode used for one left-turn movement on a road is also typically used for the other opposing left-turn movement. For example, if one left-turn movement is permissive, the opposing left turn is also permissive. However, this agreement is not required and the decision of mode should be movement-specific based on factors such as sight distance, volumes, number of turning lanes, number of opposing lanes, and leading vs lagging left turn operation.
A variety of guidelines exist that have been developed to indicate conditions where the benefits of a left-turn phase typically outweigh its adverse impact to intersection operation. Many of these guidelines indicate that a left-turn phase can be justified based on consideration of several factors that ultimately tie back to the operational or safety benefits derived. These factors include:. The flowchart shown in Figure can be used to assist in the determination of whether a left-turn phase is needed and whether the operational mode should be protected or protected-permissive.
These guidelines were derived from a variety of sources 8;9. Application of the flowchart requires the separate evaluation of each left-turn movement on the subject road. Figure Guidelines for determining the potential need for a left-turn phase. The objective of the flow chart is to identify the least restrictive left-turn operational mode.
A secondary objective is to provide a structured procedure for the evaluation of left-turn phasing for the purpose of promoting consistency in left-turn phase application. The critical left-turn crash counts identified in the figure are based on an underlying average critical crash frequency and recognize the inherent variability of crash data. The underlying averages are 1. If the reported crash count for existing permissive operation exceeds the critical value, then it is likely that the subject intersection has an average left-turn crash frequency that exceeds the aforementioned average 5 percent chance of error and a more restrictive operational mode would likely improve the safety of the left-turn maneuver.
The flowchart has two alternative paths following the check of opposing traffic speed. One path requires knowledge of left-turn delay; the other requires knowledge of the left-turn and opposing through volumes. The left-turn delay referred to in the flowchart is the delay incurred when no left-turn phase is provided i. It may be advantageous under certain circumstances to change the sequence in which left turns are served relative to their complementary through movements.
This is done by reversing the sequence of a pair of complementary phases, as is shown for phases 1 and 2 in Figure Specifically, Figure shows phases 2 and 6 starting and ending at different times in the cycle. This independence between the through phases can be desirable under coordinated operations because it can accommodate platoons of traffic arriving from each direction at different times. The most commonly used left-turn phase sequence is the "lead-lead" sequence which has both opposing left-turn phases starting at the same time.
If a single ring structure is used, then the two phases also end at the same time. If an actuated dual ring structure is used, then each left-turn phase 14 is assigned to a different ring such that each can end when the left-turn demand is served i.
The advantages of this phasing option are: 1 that drivers react quickly to the leading green arrow indication and 2 it minimizes conflicts between left-turn and through movements on the same approach, especially when the left-turn volume exceeds its available storage length or no left-turn lane is provided. A more detailed discussion of the advantages of leading left-turn phases is provided in Chapter 13 of the Traffic Engineering Handbook This left-turn phase sequence is most commonly used in coordinated systems with closely spaced signals, such as diamond interchanges.
It has both opposing left-turn phases ending at the same time. If it is implemented in a single ring structure, then the two phases also start at the same time. If a dual-ring structure is used, then each left-turn phase is assigned to a different ring such that each can start when the left-turn demand is served i. Lagging left-turn phasing is also recognized to offer operational benefits for the following special situations:.
When used with protected phasing, this phase sequence provides a similar operational efficiency as a lead-lead or lead-lag phase sequences. However, differences emerge when they are used with protected-permissive mode.
One disadvantage of lagging left-turn phases is that drivers tend not to react as quickly to the green arrow indication. Another disadvantage is that, if a left-turn bay does not exist or is relatively short, then queued left-turn vehicles may block the inside through lane during the initial through movement phase.
When lag-lag phasing is used at a four-leg intersection where both phases are used with the protected-permissive mode, then both left-turn phases must start at the same time to avoid the "yellow trap" or left-turn trap problem, illustrated in Figure This problem stems from the potential conflict between left-turning vehicles and oncoming vehicles at the end of the adjacent through phase.
Of the two through movement phases serving the subject street, the trap is associated with the first through movement phase to terminate and occurs during this phase's change period. The left-turn driver seeking a gap in oncoming traffic during the through phase, first sees the yellow ball indication; then incorrectly assumes that the oncoming traffic also sees a yellow indication; and then turns across the oncoming traffic stream without regard to the availability of a safe gap.
In fact, under at least one condition, the second technique can operate more efficiently than dual-ring lead-lead phasing. This condition occurs when the left-turn volume is moderate to heavy and relatively equal on both approaches. Regardless, a detailed operational evaluation should always be used to confirm that lag-lag phasing operates more efficiently than other phasing options.
The third technique avoids the yellow trap by using an overlap in the controller and a five-section left-turn signal head. An overlap is a controller output to the signal head load switch that is associated with two or more phases. In this application, the left-turn green and yellow arrow indications are associated with the subject left-turn phase; and the left-turn green, yellow, and red ball indications are associated with the opposing through movement phase as opposed to those of the adjacent through phase.
The flashing yellow arrow is contained within a three-, four-, or five-section head and provides a permissive indication to the driver that operates concurrent with the opposing through movement rather than the adjacent through movement.
This study was conducted over a 7-year period and comprised a very comprehensive research process, including engineering analyses, static and video-based driver comprehension studies, field implementation, video conflict studies, and crash analyses.
This study 11 recommended that a flashing yellow arrow be allowed as an alternative to the circular green for permissive left-turn intervals. The louvered signal head is referred to as the "Dallas Display. This left-turn phase sequence is generally used to accommodate through movement progression in a coordinated signal system. The aforementioned "yellow trap" may occur if the leading left-turn movement operates in the protected-permissive mode and the two through movement phases time concurrently during a portion of the cycle.
The "yellow trap" problem can be alleviated by using one of the following techniques:. The first two techniques will likely have an adverse effect on operations, relative to a dual ring implementation of lead-lag phasing with protected-permissive operation. However, they avoid the potential adverse effect a yellow trap would have on safety.
However, in practice, the Dallas Display is used for both the leading and the lagging left-turn signal heads because it improves operational performance Lead-lag phasing is also recognized to offer operational benefits for the following special situations:. Pedestrian movements are typically served concurrently with the adjacent through movement phase at an intersection. This is done to simplify the operation of the intersection primarily and is largely a legacy issue in our application of signal logic and control.
Typical application of pedestrian operation puts pedestrians in conflict with right-turning vehicles and left-turning vehicles that operate in a permissive mode, by inviting their movement at the same time.
There are specific measures that can be used to mitigate this potential conflict, three common options include:. Figure Ring-barrier diagrams showing a leading pedestrian interval and an exclusive pedestrian phase. Two types of right-turn phasing are addressed in this section. The first type is based on the addition of a phase to the signal cycle that exclusively serves one or more right-turn movements. This type of right-turn phasing is rarely used.
If it is being considered, then its operational or safety benefits should be evaluated and shown to outweigh its adverse impact on the efficiency of the other intersection movements. The second type of right-turn phasing is based on the assignment of the right-turn movement to the phase serving the complementary left-turn movement on the crossroad. The following conditions should be satisfied before using this type of right-turn phasing:. If the aforementioned conditions are satisfied, then the appropriate operational mode can be determined.
If the through movement phase for the subject intersection approach serves a pedestrian movement, then the right-turn phasing should operate in the protected-permissive mode. As shown in Figure , the permissive right-turn operation would occur during the adjacent through movement phase, and the protected right-turn operation would occur during the complementary left-turn phase.
If the through movement phase for the subject intersection approach does not serve a pedestrian movement, then the right-turn phasing should operate in the protected only mode during both the adjacent through movement phase and the complementary left-turn phase. A controller overlap may be used to provide this sequence. Detectors place calls into the traffic signal controller. The controller uses this information and the signal timing to determine the display provided to the users.
Detection for pedestrians is limited in most cases to push buttons as shown in Figure , although accessible 20 pedestrian signal detectors are increasing in their use. There are various forms of vehicle detection technologies, and strengths and weaknesses of each are described in the Traffic Detector Handbook, 3rd edition The detection design for an intersection describes the size, number, location, and functionality of each detector.
Most engineering drawings include the wiring diagram for how detectors are associated to phases. Signal timing settings such as the passage time, delay, extend, and other related parameters are described in more detail in Chapter 5. The size and location of detectors is an important element in traffic signal design. Detectors can consist of one 6-foot-byfoot inductive loop detector, a series of closely spaced 6-foot-byfoot loop detectors may be circular in shape as shown in Figure , one long 6-foot-byfoot loop detector, or alternative detection technology e.
This detection zone can be used to meet the objectives described below. A call can be triggered by an actuation from any detection, vehicular, pedestrian, or other or through a controller function.
These parameters are described in Chapter 5. The objective of detection is to detect vehicle presence and identify gaps in vehicle presence that are sufficiently long to warrant terminating the phase. There are many objectives of detection design that can be characterized with the following statements:.
The first and fourth objectives are safety related. The first objective addresses expectancy, while the fourth specifically addresses the potential crashes as a result of phase termination. The fourth objective is achieved by using advance detectors on the approach.
The location of these detectors can vary and depends on the detection technology used as well as intersection approach speed. The safety benefit of this design tends to be more significant on high-speed approaches. The other objectives focus on intersection efficiency. The second and third objectives are designed to address efficiency. During low volume late night or off-peak conditions, detection should seek to serve all traffic identified without stopping.
Every 2 hours observers should take a 10 to 15 minute break. Perform necessary office preparations. Select proper observer location. Label data sheets and record observations. Perform Necessary Office Preparations Office preparations start with a review of the purpose of the manual count. This type of information will help determine the type of equipment to use, the field procedures to follow, and the number of observers required. For example, an intersection with multiple approach lanes may require electronic counting boards and multiple observers.
Select Proper Observer Location Observers must be positioned where they have a clear view of the traffic. Observers should be positioned away from the edge of the roadway.
If observers are positioned above ground level and clear of obstructions they usually have the best vantage point. Visual contact must be maintained if there are multiple observers at a site. If views are unobstructed, observers may count from inside a vehicle. On each tally sheet a blank tally sheet is provided in Appendix B , the observer should record the location, time and date of observation, and weather conditions.
Follow the data recording methods discussed earlier. The proposal was to remove four houses and construct an apartment complex see Figure 3. This proposed land use change would affect traffic volume. The city wanted to document the traffic volumes at the closest intersection during the peak flow period of the day. The study was conducted at the intersection of 7th Street and Delaware Avenue, an uncontrolled intersection.
The time period chosen, a. Figure 3. Example Proposed Apartment Complex and Intersection 3. The example tally sheet in Figure 3. There were 71 westbound vehicles on Delaware Avenue. If you multiply this number by eight eight minute periods in a 2-hour peak flow , you arrive at vehicles during the peak flow. Typically 2-hour peak flow counts would be conducted once in the morning and once in the afternoon.
If an apartment complex is introduced, another study may need to be conducted. The apartment complex could increase the traffic volume. If the traffic volume is increased, there may be a need for new traffic control. The initial study provides a baseline count that can be used in a traffic impact analysis or a traffic control device evaluation.
The Manual on Uniform Traffic Control Devices provides current standards on traffic control device warrants. Information on contracting for a traffic volume count study, including a project work order using the Smith City example, is provided near the end of this chapter.
Record school buses with SB. Automatic counts are usually taken in 1-hour intervals for each hour period. The counts may extend for a week, month, or year. When the counts are recorded for each hour time period, the peak flow period can be identified. Aut om a t ic Count Re c ording M e t hods Automatic counts are recorded using one of three methods: portable counters, permanent counters, and videotape. Portable Counters Portable counting is a form of manual observation.
Portable counters serve the same purpose as manual counts but with automatic counting equipment. The period of data collection using this method is usually longer than when using manual counts. The portable counter method is mainly used for hour counts. Pneumatic road tubes are used to conduct this method of automatic counts see Figure 3.
Recorder Figure 3. The counts could be performed every day for a year or more. The data collected may be used to monitor and evaluate traffic volumes and trends over a long period of time. Permanent counters are not a cost-effective option in most situations. Few jurisdictions have access to this equipment. Videotape Observers can record count data by videotaping traffic. Traffic Direction and Control A.
When directing traffic, the following rules will be observed: 1. Officers will utilize the police whistle or voice commands depending on the situation. Search the Manual: Go!
0コメント