When roads are being constructed, one of the most common pieces of the traffic control plan is a taper. Tapers, simply put, are signs or devices, or pavement marks, which move traffic into a temporary path to keep it clear of the construction.
When I talk about upstream and downstream, that’s where traffic is approaching or leaving the construction zone, which we also call the transition and termination areas. There are five types of tapers:
- One-Lane Two-Way Taper
Traffic going in each direction alternates in passing through the control area, typically directed by temporary control signals or a flagger.
- Shoulder Closure Taper
Usually seen on high-speed roads, where traffic might mistake the shoulder of the road as a driving lane.
- Merging Taper
Sometimes the most frustrating taper for drivers, as it has traffic merging from two or more lanes down into one.
- Shifting Taper
With a shifting taper, traffic doesn’t have to merge, but lanes shift laterally, most often onto the roadway shoulder.
- Downstream Taper
We see these in the termination area, to let drivers know that they can now use the original roadway that had been closed.
The taper length criteria and spacing of devices are based on formulas using the speed of the traffic and width of the offset (lane width). There are also other considerations when tapers are implemented.
Existing lane widths of through roadways should be maintained through the work zone travel way wherever practical. The minimum width for work zone travel lanes shall be 10 feet for all roadways other than Interstate.
Pacing Specifications (Rolling Roadblock)
A technical special provision is required to pace traffic for up to twenty (20) minutes maximum to allow work in or above all lanes of traffic for the following:
- Placing bridge members
- Placing overhead sign structures
- Other items requiring interruption of traffic
- Detours redirect traffic onto an alternate route, using state roads, county roads or city streets to bypass the work zone
- Diversion are special detours onto a temporary roadway adjacent to the existing or permanent roadway
- Lane shifts redirect of traffic onto a section of permanent roadway or shoulder
Work duration is a major factor in determining the number and types of devices used in temporary traffic control zones. The five categories of work duration and their time at a location shall be:
- Long term stationary (more than three days)
- Intermediate-term stationary (more than one daylight period up to three days or night time work more than one hour)
- Short-term stationary is daytime work that occupies a location for more than one hour but less than 12 hours
- Short duration is work that occupies a location up to one hour
- Mobile is work that moves intermittently or continuously
Ensuring safe traffic flow is helped substantially by tapers and how they’re employed. But there are other considerations to include. One that I mentioned earlier in this post is the use of flaggers, and I’ll discuss that in my next traffic control plan post.