A Guide to Oregon Diagram 320

Stationary Lane Closure with Flagging: Key Guidelines and Best Practices

Managing temporary traffic control on two-lane, two-way roadways is essential to ensuring safety for both workers and motorists. The Oregon Temporary Traffic Control Handbook (OTTCH) provides clear instructions for handling these situations, particularly when a lane closure is required. Below is a summary of key points from Diagram 320, which addresses the closure of one lane with flagging operations.

1. Flagging Overview

When one lane is closed on a two-lane, two-way roadway, it’s important to follow specific protocols to ensure the smooth flow of traffic and the safety of all involved. These operations often require the use of flaggers, truck-mounted equipment, and signage. Special attention must be paid to traffic volume, sight distance, and other environmental factors.

2. Use of Truck-Mounted Warning Lights

To enhance visibility and communication with motorists:

  • Truck-mounted flashing warning lights are required on both work and protection vehicles.
  • A truck-mounted arrow board or portable changeable message sign (PCMS) in caution mode may also be used for additional visibility.

3. Conditions Requiring Flaggers

Flaggers are critical in controlling traffic flow during lane closures. You will need flaggers at each approach if:

  • Night operations are taking place.
  • The work space extends over 200 feet in length.
  • Sight distance is less than 750 feet from each approach.
  • Traffic volumes exceed 400 Average Daily Traffic (ADT).

4. Limitations on Distance Between Flaggers

For lane closures not exceeding one mile, standard flagging can be used. However, if the lane closure extends beyond one mile, it is necessary to utilize a pilot car system, as outlined in Diagram 340.

5. Use of Cones for Safety

Cones are a vital safety feature:

  • They should outline the work space if curves or road alignments hinder motorists from passing safely.
  • Cones along the work space are highly recommended when the posted speed is 45 mph or higher, or when traffic is heavy, or travel lanes are narrower than 11 feet.
  • Don’t forget your flagger taper!

6. Queue and Intersection Management

To manage traffic queues:

  • Extended queue signing should be employed when queues extend beyond the initial advance warning sign.
  • If flagging occurs near intersections, the “Flagger Ahead” sign should be visible to traffic coming from side roads. Additional warning signs may be placed on these side roads to ensure proper alertness.

7. Intermittent Full Road Closures

In cases where intermittent full road closures are necessary, the set-up and flagger placement outlined in Diagram 320 may be used for closures lasting 20 minutes or less.

8. Sign Spacing and Buffer Lengths

To maximize safety and give motorists ample time to respond, proper spacing between signs and buffer lengths are critical. The Oregon Temporary Traffic Control Handbook provides the following guidelines:

Posted Speed (mph)Sign Spacing (ft)Buffer Space (ft)
2010050
2510075
30100100
35350125
40350150
45500180
50500210
55500250

Remember, the goal is to keep everyone safe: By following these guidelines, we can minimize disruptions and ensure a smooth traffic flow.

So, next time you’re stuck behind a lane closure, remember the folks working hard to keep you safe!

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