(This article on work zone safety is reproduced from the April 1990 (Volume 8, No. 4) issue of the TranSafety Reporter, published and edited by Roy W. Anderson, P.E. To find legal summaries of cases related to highway work zones, please check on-line editions of Road Injury Prevention and Litigation Journal at this web site.)

The California Department of Transportation (Caltrans) has issued a revision to Chapter 5 of its Traffic Manual. Chapter 5 is also published separately as the Manual of Traffic Controls for Construction and Maintenance Work Zones. The new revision, which became effective January 1, 1990, updates the 1985 edition. The new revision provides a general updating and among the more significant changes are:

• New emphasis on the requirement that Traffic Control Plans (TCP) be developed for all projects.
• Update of new warning signs and policies for their use.
• Added MUTCD requirements that provide that "barricades shall have a minimum of 270 square inches of retroreflective area facing traffic when used on freeways, expressways, and other high speed highways."
• Added a discussion on the use of crash cushions in work zones.
• Added a discussion on the use of glare screens and "gawking" screens in work zones.
• Added a new section on "Temporary Markings."
• Added a new section, "Principles of Work Zone Traffic Control," which discusses the five basic areas within a work zone. It also discusses taper length criteria and provides formulas to calculate the various conditions.

As the readers of this column are well aware, I feel that a well-designed traffic control plan is one of the most important elements for providing safety for the public and workers in highway work zones, whether a low-speed street or a high-speed freeway. Caltrans quite clearly feels that stronger emphasis on the TCP is required. This comes from the state that was a pioneer in work zone safety practices. It is also from a state whose work zone traffic controls on Caltrans-administered highways are generally superior to those I have observed in most other states.

The provisions in the revised Traffic Manual provide that:

It is not clear why Caltrans used the phrase "must be developed." The word "must" is not defined in the Manual as are the words "shall, should, and may." I would interpret the "must" as "shall."

The Traffic Manual goes on to provide the requirements for the TCP:

The Traffic Manual provides that on portable concrete barriers the effect of impacting the ends of the barriers should be mitigated. "Such mitigating measures include the use of crash cushions or flaring the ends of barriers away from the traveled way at a rate of 1:10 or flatter (1 foot of lateral offset for every 10 feet of barrier length)."

For the screening of work areas Caltrans states that "screens improve traffic flow where traffic volumes approach the roadway capacity because they discourage 'gawking.' Likewise, they may increase safety under such conditions." They go on to warn that screens should not be mounted where "they restrict driver visibility and sight distance."

Caltrans states that most work zones can be divided into five areas as illustrated in Figure 1. The Manual provides a description of each of the elements.

Figure 1.   Areas in Traffic Control Zone

Caltrans believes that the single most important element within the system of traffic control devices commonly used in work zones where a reduction in pavement width is involved is the taper that is provided for the channelization in the transition area. "An inadequate taper will almost always produce undesirable traffic operations, with resulting congestion and increased possibility of accidents." According to Caltrans the "real test" of adequate taper length is the operation of vehicles through the transition. "A brief period of observing driver performances will generally provide some clear indication of the adequacy of the taper length." They note that "if severe brake operations are observed during free flow traffic conditions, an increased taper length is indicated."