IMSA Work Zone cheat sheet

MUTCD Part 6 governs temporary traffic control; all TTC devices must meet the applicable crashworthiness criteria when placed within the clear zone.

A TTC zone has four sequential components: advance warning area, transition area, activity area (made up of buffer space, work space, and traffic space), and termination area.

Merging taper length is L = W x S when the posted speed S is 40 mph or less, where W is the offset width in feet and S is the speed in mph.

Merging taper length is L = W x S squared / 60 when the posted speed S is 45 mph or more.

Traffic space is the portion of the activity area open to road users; work space and traffic space must never occupy the same area.

Buffer space is a separation containing no workers, equipment, or material; its purpose is to give an errant vehicle room to recover before reaching the work space.

Duration categories: long-term stationary exceeds 3 consecutive days, short duration is up to 1 hour, and mobile operations move continuously or intermittently.

A posted speed limit may be changed in a TTC zone only by the governing highway agency through ordinance or resolution; a warning sign alone does not alter the regulatory limit.

MUTCD statement types are Standard (mandatory), Guidance (recommended), Option (permitted), and Support (informational); only Standards create a mandatory requirement.

Orange is the background color for warning signs used in TTC zones, with black legend and border; fluorescent yellow-green is reserved for other warning applications.

Cones must be at least 18 in tall for daytime use where the posted speed is 45 mph or less, and at least 28 in tall for nighttime use or posted speeds above 45 mph.

Drums are at least 36 in tall and at least 18 in in diameter, with alternating retroreflective stripes, and are used where higher speeds or longer durations warrant more conspicuous channelization.

Type I barricades have one horizontal rail, Type II have two, and Type III have three rails with large panels and are the type used to close a road or ramp.

The flagger STOP/SLOW paddle is a rigid octagon at least 18 in wide; the flag is a red or fluorescent red-orange flag at least 24 in square.

Arrow panels are 48 in minimum for posted speeds of 45 mph and above, and 36 in minimum for lower posted speeds.

Warning-light types: Type A is low intensity (steady or flashing), Type B is high-intensity flashing, and Type C is steady burn.

All channelizing devices, barricades, and sign supports placed within the clear zone must be crashworthy and, where required, retroreflectorized.

Shifting taper length is one-half of the merging taper length for the same speed and offset; shoulder taper length is one-third of the merging taper length.

A one-lane, two-way traffic taper is a minimum of 100 ft long and tapers traffic to the centerline for control by flaggers or temporary signals.

The downstream taper in the termination area is 50 ft to 100 ft long and returns traffic to its normal path.

The activity area consists of buffer space, work space, and traffic space, arranged in that order from the transition area toward the termination area.

Advance warning area length increases with posted speed and is measured from the first warning device to the beginning of the transition area.

Flagger stations are sited ahead of the work space with unobstructed sight distance to approaching traffic and a clear escape path off the traveled way.

Pedestrian access routes through or around a TTC zone must be maintained, with channelizing barriers and detectable warnings where the path changes.

In high-speed or nighttime conditions, drums and retroreflectorized devices are used in place of plain cones, and all devices are checked for legibility and cleanliness.

Workers within the right-of-way of a federal-aid highway must wear ANSI/ISEA 107 Class 2 or 3 high-visibility apparel; Class 3 is required for nighttime work.

Roughly 80 to 85 percent of work zone fatalities are vehicle occupants rather than workers, so roadway user protection drives much of the layout design.

Positive protection (temporary traffic barriers, crash cushions, attenuator trucks) is used where workers cannot be separated from traffic by distance or channelization alone.

A shadow vehicle with a truck-mounted attenuator is positioned upstream of the taper, in advance of the work space, to absorb impacts from errant vehicles.

A flagger stands outside the traveled way, never in an open lane, and controls only one direction of traffic at a time unless coordination is established.

Intrusion alarms and warning devices are used in work spaces adjacent to open traffic to alert workers to errant vehicles.

Reducing the duration of exposure through off-peak scheduling and shorter work areas lowers both worker and road user risk.

TTC zones are inspected at the start of each shift and after any change in weather, traffic, or work activity that could alter the layout.

Inspection items include device position, sign legibility, retroreflectivity, warning-light operation, ballast, and channelizing device spacing.

Night inspections verify that retroreflective devices and warning lights perform under actual or simulated nighttime conditions.

Each inspection is documented with date, time, inspector, devices checked, deficiencies found, and the time corrections were completed.

The TTC plan, daily logs, photographs of the zone as set up and as modified, and device inventory are retained as the compliance record.

Damage or loss of devices is recorded and the replacement time is logged to show the zone was maintained in the approved configuration.

A TTC zone must provide continuity of guidance so that road users are directed along a clear, unambiguous path through or around the work area.

Devices not needed for the current work activity should be removed; obsolete or conflicting signs are removed or covered to avoid contradictory messages.

Temporary traffic control must accommodate all road users including pedestrians, bicyclists, and accessible routes.

The type and number of devices deployed is determined by road type, speed, volume, work duration, and location of the work relative to traffic.

The four TTC zone components remain the same regardless of work duration; only the extent and conspicuity of devices change.

Where two-way traffic uses a single lane, control is by flagger, temporary signal, or yield control per the approved traffic control plan.