Q.: While riding on an urban expressway recently we came to a construction area where ramp traffic and some expressway traffic were being redirected by means of precast concrete safety barriers about 3 feet high. Although using these barriers seems to me to be a good practice ordinarily, I was distressed to see that intervals of about 2 feet had been left between individual sections of the barriers. I believe that this negates the safety of the barrier. Are there any standards that require adjoining sections to be touching one another, or that at least limit the gaps to an inch or two?
A.: You are right about your concern. The way these modern safety barriers function is to direct the impinging front wheel up the side of the barrier. This lifting of the car uses up some of the energy and lets the car slide back down without being thrown across the highway. If a considerable amount of space is left between barrier sections, the wheel will inevitably get caught in that space, possibly causing the car to spin around or turn over and cause a great hazard to nearby traffic.
The correct way to set safety barriers is set forth in the Manual of Uniform Traffic Control Devices, 1983 edition, published by the Federal Highways Administration Washington, DC. It says "The connecting devices must be strong enough to ensure that the individual elements act as a smooth continuous barrier. For some applications it may be necessary to anchor the concrete barrier to prevent lateral movement if hit by a vehicle. This can be accomplished with drift pins or anchor bolts placed in holes drilled in the pavement or bridge structure." The Manual also points out that "On construction projects, particular attention is needed for connecting portable or temporary barriers to adjacent existing barriers or guardrails. The construction plans should provide details for this. All connections should develop the full strength of the barrier system(s)." Additional information is given in Guide for Selecting, Locating and Designing Traffic Barriers, published by the American Association of State Highway and Transportation Officials, Washington, DC.