616.2 Temporary Traffic Control Elements (MUTCD Chapter 6B)

616.2.1 Temporary Traffic Control Plans (MUTCD Section 6B.01)

Support. Each TTC zone is different. Many variables, such as location of work, highway type, geometrics, vertical and horizontal alignment, intersections, interchanges, road user volumes, road user mix (motorists, bicyclists, and pedestrians), road vehicle mix (buses, trucks, and cars), and road user speeds affect the needs of each zone. The goal of TTC in work zones is safety with minimum disruption to road users. The key factor in promoting TTC zone safety is proper judgment.

A TTC plan describes TTC measures to be used for facilitating road users through a work zone or an incident area. TTC plans play a vital role in facilitating road user flow when a work zone, incident, or other event temporarily disrupts normal road user flow. Important auxiliary provisions that cannot conveniently be specified on project plans can easily be incorporated into Special Provisions within the TTC plan.

TTC plans range in scope from being very detailed to simply referencing typical drawings contained in the EPG, Missouri Standard Plans for Highway Construction, or specific drawings contained in the contract documents. The degree of detail in the TTC plan depends entirely on the nature and complexity of the situation.

The TTC plan is an integral part of the planning and design of a project. The scope of the TTC plan is determined by the complexity of the project and is developed by the designer in the district in cooperation with district construction, maintenance, and traffic staff.

Standard. A TTC plan shall be developed for every project. Typical traffic control set-ups shall be shown for each work activity within the work zone. The location of all traffic control devices shall be provided in the TTC plan.

Guidance. When staged construction is used, the stages should be clearly defined in the TTC plan. Each stage should have a description of the type of work being done during that phase. Stationing is to be shown, if applicable.

A preliminary field check with district construction and traffic should be conducted to ensure the TTC plan will be compatible with field conditions.

Option. Traffic count data may be obtained from Transportation Planning to aid in the development of the TTC plan. This is especially the case where traffic capacity is a significant factor in the design of the TTC plan. Intersection traffic count data may also be requested from district traffic personnel. Hourly volumes can assist in determining the type of traffic control used, working hour restrictions and other aspects of the TTC plan. The use of Highway Capacity Software, VISSIM, CORSIM or other computer programs may aid in estimating queue lengths, delays, etc. resulting from the work zone.

Support. For additional information related to traffic flow through work zones, see EPG 616.19.

For additional plan sheet guidance see EPG 237.

During TTC activities, commercial vehicles might need to follow a different route from passenger vehicles because of bridge, weight, clearance, or geometric restrictions. Also, vehicles carrying hazardous materials might need to follow a different route from other vehicles.

Guidance. A TTC plan should be developed for planned activities that will affect road users. A TTC plan should be developed for unplanned and emergency situations where practicable. Consideration should also be given to snow plowing operations in TTC zones.

The TTC plan should start in the planning phase and continue through the design, construction, and restoration phases. The TTC plans and devices should follow the principles set forth in EPG 616. The management of traffic incidents should follow the principles set forth in EPG 616.15.

TTC plans should be prepared by persons knowledgeable (for example, trained and/or certified) about the fundamental principles of TTC and work activities to be performed. The design, selection, and placement of TTC devices for a TTC plan should be based on engineering judgment. Designers should be familiar with the traffic control sheets of the Missouri Standard Plans for Highway Construction and the Missouri Standard Specifications for Highway Construction.

Coordination should be made between adjacent or overlapping projects to check that duplicate signing is not used and to check compatibility of traffic control between adjacent or overlapping projects.

Traffic control planning should be completed for all highway construction, utility work, maintenance operations, and incident management including minor maintenance and utility projects prior to occupying the TTC zone. Planning for all road users should be included in the process.

For any planned special event that will have an impact on the traffic on any street or highway, a TTC plan should be developed in conjunction with and be approved by MoDOT district staff and/or agencies that have jurisdiction over the affected roadways.

Provisions for effective continuity of accessible circulation paths for pedestrians should be incorporated into the TTC plan.

Option. Provisions may be incorporated into the project bid documents that enable contractors to develop an alternate TTC plan.

Modifications of TTC plans may be necessary because of changed conditions or a determination of better methods of safely and efficiently handling road users.

Guidance. This alternate or modified plan should have the approval of the responsible highway agency or owner of site roadways open to public travel prior to implementation.

Provisions for effective continuity of transit service should be incorporated into the TTC planning process because often public transit buses cannot efficiently be detoured in the same manner as other vehicles (particularly for short-term maintenance projects). Where applicable, the TTC plan should provide for features such as accessible temporary bus stops, pull-outs, and satisfactory waiting areas for transit patrons, including persons with disabilities (see EPG 913.1.13 for additional light rail transit issues to consider for TTC).

Provisions for effective continuity of railroad service and acceptable access to abutting property owners and businesses should also be incorporated into the TTC planning process.

Reduced speed zoning (lowering the regulatory speed limit) should be avoided as much as practical because drivers will reduce their speeds only if they clearly perceive a need to do so.

If reduced speed limits are used, they should be used only in the specific portion of the TTC zone where conditions or restrictive features are present. However, frequent changes in the speed limit should be avoided.

Support. See EPG 616.18 for additional provisions regarding work zone speed limits.

EPG 616.16 contains typical applications (TAs) of TTC zones that are organized according to duration, location, type of work, and highway type. Table 6P-1 of the MUTCD is an index of these typical applications for contract projects (see EPG 616.16.2). EPG 616.16.3 includes typical applications for internal use by MoDOT employees. These typical applications include the use of various TTC methods, but do not include a layout for every conceivable work situation.

Decisions regarding the selection of the most appropriate typical application to use as a guide for a specific TTC zone require an understanding of each situation. Although there are many ways of categorizing TTC zone applications, the typical applications are characterized by work duration, work location, work type, and highway type.

Guidance. Typical applications should be altered, when necessary, to fit the conditions of a particular TTC zone.

Option. Other devices may be added to supplement the devices shown in the typical applications. The sign spacings and taper lengths may be increased to provide additional time or space for driver response.

Devices labeled as optional in the typical applications may be deleted.

Support. Formulating specific plans for TTC at traffic incidents is difficult because of the variety of situations that can arise.

Well-designed TTC plans for planned special events will likely be developed from a combination of treatments from several of the typical applications.

616.2.2 Temporary Traffic Control Zones (MUTCD Section 6B.02)

Support. A TTC zone is an area of a highway where road user conditions are changed because of a work zone, an incident zone, or a planned special event through the use of TTC devices, uniformed law enforcement officers, or other authorized personnel.

A work zone is an area of a highway with construction, maintenance, or utility work activities. A work zone is typically marked by signs, channelizing devices, barriers, pavement markings, and/or work vehicles. It extends from the first warning sign or high-intensity rotating, flashing, oscillating, or strobe lights on a vehicle to the END ROAD WORK sign or the last TTC device.

An incident zone is an area of a highway where temporary traffic controls are imposed by authorized officials in response to a traffic incident (see EPG 616.15). It extends from the first warning device (such as a sign, light, or cone) to the last TTC device or to a point where road users return to the original lane alignment and are clear of the incident.

A planned special event often creates the need to establish altered traffic patterns to handle the increased traffic volumes generated by the event. The size of the TTC zone associated with a planned special event can be small, such as closing a street for a festival, or can extend throughout a municipality for larger events. The duration of the TTC zone is determined by the duration of the planned special event.

616.2.3 Components of Temporary Traffic Control Zones (MUTCD Section 6B.03)

Support. A TTC zone is often divided into four areas as needed, based on engineering judgment: the advance warning area, the transition area, the activity area (which includes workspace and buffer spaces), and the termination area. Figure 616.2.3 illustrates the four areas typically included in a TTC zone. These four areas are described in EPG 616.2.4 through EPG 616.2.7.

Figure 616.2.3 Component Parts of a Temporary Traffic Control Zone

616.2.4 Advance Warning Area (MUTCD Section 6B.04)

Support. The advance warning area is the section of highway where road users are informed about the upcoming transition and activity areas or incident area.

Option. The advance warning area may vary from a single sign or high-intensity rotating, flashing, oscillating, or strobe lights on a vehicle to a series of signs in advance of the TTC zone activity area.

Guidance. The signs or other warning devices should be positioned to give the driver sufficient time to react to the conditions. Warning devices should not be placed too far in advance, as the warning message will lose effectiveness.

Typical distances for placement of advance warning signs on freeways and expressways should be longer because drivers are conditioned to uninterrupted flow. Therefore, the advance warning sign placement should extend on these facilities as far as ½ mile or more.

On urban streets, the effective placement of the nearest warning sign to the TTC zone, in feet, should range from 4 to 8 times the speed limit in mph, with the high end of the range being used when speeds are relatively high. When two or more advance warning signs are used on higher-speed streets, such as major arterials, the advance warning area should extend a greater distance (see Table 616.2.4).

Option. When a single advance warning sign is used (in cases such as low-speed residential streets), the advance warning area may be as short as 100 feet.

Guidance. Since rural highways are normally characterized by higher speeds, the effective placement of the first warning sign in feet should be substantially longer—from 8 to 12 times the speed limit in mph. Since two or more advance warning signs are normally used for these conditions, the advance warning area should extend 1,500 feet or more for open highway conditions (see Table 616.2.4).

Table 616.2.4 Recommended Advance Warning Sign Minimum Spacing

Road Type	Distance between Signs*
	A	B	C
Urban (35 mph or less)	100 feet	100 feet	100 feet
Urban (40 mph or more)	350 feet	350 feet	350 feet
Rural	500 feet	500 feet	500 feet
Expressway/Freeway	1,000 feet	1,500 feet	2,640 feet
* The column headings A, B, C are the dimensions shown in MUTCD Figures 6P-1 through 6P-54. The A dimension is the distance from the transition or point of restriction to the first sign. The B dimension is the distance between the first and second signs. The C dimension is the distance between the second and third signs. (The "first sign" is the sign in a three-sign series that is closest to the TC zone. The "third sign" is the sign that is furthest upstream from the TTC zone.) Note: See Table 616.16.3.3 for MoDOT internal use

The distances contained in Table 616.2.4 are approximate, are intended for guidance purposes only, and should be applied with engineering judgment. These distances should be adjusted for field conditions, if necessary, by increasing or decreasing the recommended distances.

Support. The need to provide additional reaction time for a condition is one example of justification for increasing the sign spacing. Conversely, decreasing the sign spacing might be justified in order to place a sign immediately downstream of an intersection or major driveway such that traffic turning onto the roadway in the direction of the TTC zone will be warned of the upcoming condition.

Option. Advance warning may be eliminated when the activity area is sufficiently removed from the road users’ path so that it does not interfere with the normal flow.

In some cases on high volume routes, traffic backups due to the work activity may extend past the normal advance warning area. In this case, additional signing may be required to warn drivers before they reach the backup. For longer-term activities, alternate route signing and interactive devices or changeable message signs may be considered. Computer programs are available to aid in estimating back ups and delays due to work zones.

In some cases, particularly in urban areas, the advance warning area may extend through an intersection or interchange. Special considerations such as additional advance signs or adjustments to sign spacing may be needed to assure all approaching drivers are informed of the conditions.

616.2.5 Transition Area (MUTCD Section 6B.05)

Support. The transition area is that section of highway where road users are redirected out of their normal path. Transition areas usually involve strategic use of tapers, which because of their importance are discussed separately in detail.

Standard. Except for mobile operations, when redirection of the road users’ normal path is required, road users shall be directed from the normal path to a new path with appropriate channelizing devices, traffic control devices, and/or TTC methods.

Option. Because it is impracticable in mobile operations to redirect the road users’ normal path with stationary channelization, more dominant vehicle-mounted traffic control devices, such as arrow boards, portable changeable message signs, and high-intensity rotating, flashing, oscillating, or strobe lights, may be used instead of channelizing devices to establish a transition area.

616.2.6 Activity Area (MUTCD Section 6B.06)

Support. The activity area is the section of the highway where the work activity takes place. It is comprised of the work space, the traffic space, and the buffer space.

The work space is that portion of the highway closed to road users and set aside for workers, equipment, material, and a shadow vehicle, if one is used upstream. Work spaces are usually delineated for road users by channelizing devices or, to exclude vehicles and pedestrians, by temporary barriers.

Option. The work space may be stationary or may move as work progresses.

Guidance. Since there might be several work spaces (some even separated by several miles) within the project limits, each work space should be adequately signed to inform road users and reduce confusion.

Option. The workspace may be supplemented by channelizers and/or barricades placed perpendicular to the flow of traffic to deter non-construction related use of closed lanes.

Support. The traffic space is the portion of the highway in which road users are routed through the activity area.

The buffer space is a lateral and/or longitudinal area that separates road user flow from the work space or an unsafe area, and might provide some recovery space for an errant vehicle.

Guidance. Neither work activity nor storage of equipment, vehicles, or material should occur within a buffer space.

Option. Buffer spaces may be positioned either longitudinally or laterally with respect to the direction of road user flow. The activity area may contain one or more lateral or longitudinal buffer spaces.

A longitudinal buffer space may be placed in advance of a work space.

The longitudinal buffer space may also be used to separate opposing road user flows that use portions of the same traffic lane, as shown in Figure 616.2.6.

If a longitudinal buffer space is used, the values shown in Table 616.2.6 may be used to determine the length of the longitudinal buffer space.

Table 616.2.6 Stopping Sight Distance as a Function of Speed

Speed*	Distance
20 mph	115 feet
25 mph	155 feet
30 mph	200 feet
35 mph	250 feet
40 mph	305 feet
45 mph	360 feet
50 mph	425 feet
55 mph	495 feet
60 mph	570 feet
65 mph	645 feet
70 mph	730 feet
* Posted speed, off-peak 85th-percentile speed prior to work starting, or the anticipated operating speed

Support. Typically, the buffer space is formed as a traffic island and defined by channelizing devices.

When a shadow vehicle, arrow board, or changeable message sign is placed in a closed lane in advance of a work space, only the area upstream of the vehicle, arrow board, or changeable message sign constitutes the buffer space.

Option. The lateral buffer space may be used to separate the traffic space from the work space, as shown in Figures 616.2.3 and 616.2.6, or such areas as excavations or pavement-edge drop-offs. A lateral buffer space also may be used between two travel lanes, especially those carrying opposing flows.

Guidance. The width of a lateral buffer space should be determined by engineering judgment.

Option. When work occurs on a high-volume, highly-congested facility, a vehicle storage or staging space may be provided for incident response and emergency vehicles (for example, tow trucks and fire apparatus) so that these vehicles can respond quickly to road user incidents. This may involve providing storage space at the beginning or end of the activity area or both.

Guidance. Vehicle storage or staging space should not extend into any portion of the buffer space.

Figure 616.2.6 Types of Tapers and Buffer Spaces

616.2.7 Termination Area (MUTCD Section 6B.07)

Support. The termination area is the section of the highway where road users are returned to their normal driving path. The termination area extends from the downstream end of the work area to the last TTC device such as END ROAD WORK signs, if posted.

Option. An END ROAD WORK sign, a Speed Limit sign, or other signs may be used to inform road users that they can resume normal operations.

A longitudinal buffer space may be used between the work space and the beginning of the downstream taper.

616.2.8 Tapers (MUTCD Section 6B.08)

Option. Tapers may be used in both the transition and termination areas. Whenever tapers are to be used in close proximity to an interchange ramp, crossroads, curves, or other influencing factors, the length of the tapers may be adjusted.

Support. Tapers are created by using a series of channelizing devices and/or pavement markings to move traffic out of or into the normal path. Types of tapers are shown in Figure 616.2.6.

Longer tapers are not necessarily better than shorter tapers (particularly in urban areas with characteristics such as short block lengths or driveways) because extended tapers tend to encourage sluggish operation and to encourage drivers to delay lane changes unnecessarily. The test concerning adequate lengths of tapers involves observation of driver performance after TTC plans are put into effect.

Guidance. The appropriate taper length (L) should be determined using the criteria shown in Tables 616.2.8.1 and 616.2.8.2.

Table 616.2.8.1 Taper Length Criteria for Temporary Traffic Control Zones

Type of Taper	Taper Length
Merging Taper	at least L
Shifting Taper	at least 0.5 L
Shoulder Taper	at least 0.33 L
One-Lane, Two-Way Traffic Taper	100 feet
Downstream Taper	100 feet
Note: Use Table 616.2.8.2 to calculate L See Table 616.16.3.4 for MoDOT internal use

Table 616.2.8.2 Formulas for Determining Taper Length

Speed (S)	Taper Length (L) in feet
40 mph or less	$L=\frac{W{S}^2}{60}$
45 mph or more	$L=WS$
Where: L = taper length in feet W = width of offset in feet S = posted speed limit, or off-peak 85th-percentile speed prior to work starting, or the anticipated operating speed in mph Note: See Table 616.16.3.4 for MoDOT internal use

616.2.8.1 Merging Tapers

Support. A merging taper requires the longest distance because drivers are required to merge into common road space.

Guidance. A merging taper should be long enough to enable merging drivers to have adequate advance warning and sufficient length to adjust their speeds and merge into an adjacent lane before the downstream end of the transition.

Except as provided in the last Guidance paragraph of this article, merging tapers should be used to close a lane or combine traffic lanes on multilane facilities. Full-length tapers L (see Tables 616.2.8.1 and 616.2.8.2) should be used where practical. For long-term operations, lane line markings should be removed through the merging taper and temporary edge lines should be provided to guide drivers through the taper and work area.

616.2.8.2 Shifting Tapers

Support. A shifting taper is used when a lateral shift is needed. When more space is available, a longer than minimum taper distance can be beneficial. Changes in alignment can also be accomplished by using horizontal curves designed for normal highway speeds.

Guidance. A shifting taper should have a length of approximately ½ L (see Tables 616.2.8.1 and 616.2.8.2). Where shifting tapers are used, REVERSE CURVE or REVERSE TURN signs, along with any required advisory speed plaques, are to be posted prior to the shift. For long-term operations, conflicting pavement markings are removed and temporary markings provided to guide drivers through the tapers and work area. For short-term operations where it is not practical to modify pavement markings, devices should be placed at a spacing of approximately 10 feet.

616.2.8.3 Shoulder Tapers

Support. A shoulder taper might be beneficial on a high-speed roadway where shoulders are part of the activity area and are closed, or when improved shoulders might be mistaken as a driving lane. In these instances, the same type, but abbreviated, closure procedures used on a normal portion of the roadway can be used.

Guidance. If used, shoulder tapers should have a length of approximately ⅓ L (see Tables 616.2.8.1 and 616.2.8.2). If a shoulder is used as a travel lane, either through practice or during a TTC activity, a normal merging or shifting taper should be used.

616.2.8.4 Downstream or Closing Tapers

Support. A downstream (closing) taper might be useful in termination areas to provide a visual cue to the driver that access is available back into the original lane or path that was closed.

Guidance. If used, a downstream (closing) taper should have an approximate length of 100 feet with devices placed at a spacing of approximately 20 feet.

616.2.8.5 One-Lane Two-Way Tapers

Support. The one-lane, two-way taper is used in advance of an activity area that occupies part of a two-way roadway in such a manner that a portion of the road is used alternately by traffic in each direction.

Guidance. A taper having an approximate length of 100 feet with channelizing devices at approximately 20-foot spacing should be used to guide traffic into the one-lane section, and a downstream taper should be used to guide traffic back into their original lane.

Support. An example of a one-lane, two-way traffic taper is shown in Figure 616.2.8.

Figure 616.2.8 Example of a One-Lane, Two-Way Traffic Taper

Guidance. Except as provided in the paragraph below, the minimum taper length for the closure of a two-way center turn lane should be ½ L. (See Tables 616.2.8.1 and 616.2.8.2).

Option. A shorter taper length may be used when space is limited.

616.2.9 Detours and Diversions (MUTCD Section 6B.09)

Support. A detour is a temporary rerouting of road users onto an existing highway in order to avoid a TTC zone.

Detours are used when other methods of traffic control such as one-lane, two-way operations, lane closures or temporary bypasses cannot be used. Detours are provided over the shortest possible route around the closure that can sufficiently accommodate the traffic.

Guidance. Detours should be clearly signed over their entire length so that road users can easily use existing highways to return to the original highway.

Any proposed detour route should be evaluated to determine the condition of the pavement, capacity of the roadway and geometrics. The existing traffic (AADT) on the roadway being closed and the detour route, as well as the facility types should be considered when determining detour routes. State routes should be used for detours.

Option. Based on engineering judgment, projects located on routes with less than 400 AADT may not require signed detour routes.

Outer roadways may be constructed early in the project phasing or enhanced to serve as detours.

Local facilities may be considered for detours based on engineering judgement. City streets or county roads may be improved for use as detour routes

Standard. If other agencies’ facilities are used as detour routes, an agreement with the agency having jurisdiction over the roadway shall be required.

Support. A diversion is a temporary rerouting of road users onto a temporary highway or alignment placed around the work area.

Option. Alternate route signing may be used where lane closures or physical height or width restrictions will have a significant effect on traffic and a viable alternate route is available. Alternate route signing may also be used where temporary bridge weight restrictions are imposed during construction.

Support. For information regarding notification of detour routes, see EPG 616.20.3.2.2, EPG 616.20.8, and EPG 616.20.9.